Agricultural meteorology: Introduction, definition of meteorology, scope and

practical utility of Agricultural meteorology

Meteorology
The word meteoro is Greek word meaning above the earth’s surface, which is nothing but
atmosphere. Logy means subject of study or interest or science. Therefore the branch of
science dealing with atmosphere is known as meteorology. The lower atmosphere extends
up to a height of 20 km from earth’s surface, where frequent physical processes takes place
is concern of meteorology and human life.
Definition:
The science of meteorology is defined as the science that deals with the physical process
of the lower atmosphere, which produces weather.
It is a branch of physics dealing with atmosphere (Atmosphere is a deep blanket of gases
surrounding the earth). Meteorology is often quoted as the “Physics of the lower
atmosphere”. It studies the individual phenomenon of the atmosphere. In other words it is
concerned with the study of the characteristics and behaviour of the atmospheres. It
explains and analyses the changes of individual weather elements such as air pressure,
temperature and humidity that are brought about due to the effect of insolation (insolation
means radiation from the sun received by earth’s surface) on the earth’s surface.
Meteorology is the science of weather which attempts to apply physical principles to an
explanation and interpretation (meaning) of the various weather phenomena.
Meteorology is defined as the science of atmosphere and its phenomena; especially those
phenomena which we call collectively as weather and climate.
Meteorology can be organised into following parts.
1. Behaviour and properties of the atmosphere.
2. Studies of the various processes in the atmosphere.
3. Various phenomena in the atmosphere.
4. Direct and indirect effects of weather on the earth, ocean surface and life in general.
5. Application of these studies for forecasting weather.
Meteorology is essentially an observational science dealing with different atmospheric
variable such as pressure, temperature, wind, humidity, density, cloud count, radiation and
related variables at a given movement. It attempts to predict the behaviour of the
atmosphere over a period of few hours to few days ahead.
The main task of meteorology is to provide weather forecast and communicate the same
to the end user. It also helps in updating the knowledge of atmosphere.
Branches of meteorology
1. Synoptic meteorology: This branch deals with the conditions of the atmosphere at
given moment and attempts to predict change from initial condition to a period between
few hours to few days ahead by means of preparation and analysis of weather.
By definition the field of synoptic meteorology studies the relationship between the
atmosphere circulations and surface environment of the region. The basic principle is to
understand the large scale wind systems over a region and give weather forecast.
2. Dynamic meteorology: It is backbone of synoptic meteorology. It explains the
motions and energy transformations, which occurs in the atmosphere using the tools of

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mathematics and physics. It develops models based on the hydrodynamic and
thermodynamic equations. Once initial state of the atmospheric is known, the future state
can be predicted by using different equations known as Numerical Weather Prediction.
3. Physical meteorology: The approach here is of practical and experimental physics
instead of mathematics or theoretical physics. It investigate meteorological phenomenon
which are not directly link with the circulation of atmosphere. It studies the effect of
general principles that governs the transmission, absorption, emission and dispersion of
electromagnetic energy through atmosphere on radiation during concern time.
4. Statistical meteorology: This branch deals with the mean state of physical
properties of air. This branch is also called as climatology.
Climatology: Climatology is the science which treats the component elements of weather
and climate such as temperature and rainfall, their distribution over the earth and the
factors which determiners and control their distribution.
Climatology is intimately connected with geography while meteorology is closely related
to physics.
Climatology study of weather patterns over time and space. It concerns with the
integration of day to day weather over a period of time.
Discuss average conditions of the weather (Austin miller).
The values of weather elements averaged over a period like 10 years or more are known
as normal. Agricultural meteorology
Agrometeorology is a term which is abbreviated form Agricultural Meteorology
and also referred as Agroclimatology, has been defined in several ways. The name itself
implies that it is the study of those aspects of meteorology which have direct relevance to
agriculture.
Growth, development and productivity of plants depend on several factors. These factors
can be broadly divided into two major groups viz., internal factors (Genetic or hereditary)
and external or environmental (surrounding) factors. The environmental factors are
i) Climate (Meteorological elements)
ii) Edaphic (Soil)
iii) Biotic (living organisms)
iv) Physiographic (elevation)
v) Anthrophic (man)
This course on agrometeorology deals with the behaviour of the weather elements and
their effect on crop production.
Agrometeorology: Agrometeorology is a science investigating the meteorological,
climatological and hydrological conditions which are significant for agriculture owing to
their interaction with the objects and processes of agricultural production.
A science dealing with climatological conditions which have direct relation or relevance
to agriculture.
Definition given by F.A.O.: Agrometeorology is concerned with interaction between
meteorology and all the activities of man in the field of Agriculture.
In broader sense, Agrometeorology is concerned with every activity relating agriculture,
includes crops, fruit, forest and animal production and their interaction with their
environment.

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Scope of Agrometorology / The need for the study of agrometeorology
For optimum crop growth specific climatic conditions are required.
Agrometeorology thus becomes relevant to crops production because it is concerned with
the interactions between meteorological and hydrological factors on the one hand and
agriculture, in the widest sense including horticulture, animal husbandry, forestry on the
other.
Weather and climate are the important factors determining the success or failure of
agriculture. Weather influences agricultural operations from sowing of a crop to the
harvest and particularly rainfed agriculture depends on the mercy of the weather. In India
every year there is a considerable damage by floods in one part of the country and a severe
drought causing famines in another part. The total annual pre harvest losses for the
various crops are estimated from 10 to 100 per cent; while, the post-harvest losses are
estimated between 5 and 15 per cent.
Agriculture is dependent on weather more than any other aspect of human life.
Increasing climatic variability coupled with climate change and increase in the incidence
of extreme events has further necessitated the development and improvements in
agricultural meteorology. The following applications illustrate the scope of agricultural
meteorology:
Categorization of Agricultural Climate
Climatic variables like air temperature, precipitation, solar radiation, wind speed
and relative humidity are important factors on which determine the growth, development
and yield of the crop. The suitability of these parameters for increasing crop production
and economical gains in a given area are assessed by agricultural meteorology.
Crop Planning for Stability in Production
Crop planning can be carried out based on water requirements of the crop,
effective precipitation, soil moisture conditions, etc. in order to reduce risk of crop failure
on climatic part and to stabilize yields even under hostile weather situations.
Crop Management
Crop management practices like fertilizer application, plant protection, irrigation
scheduling, harvesting etc. can be carried out on the basis of specially tailored weather
support. For this purpose, operational forecasts are required.
Crop Monitoring
Meteorological tools like crop growth models, remote sensing, etc. can be used to
check the health and growth of crops.
Crop Modelling and Yield Climate Relationship
Suitable crop models, developed for the purpose provide information or predict the
results about the growth and yield using the current and past weather data.
Research in Crop–Climate Relationship
Agricultural meteorology helps to understand relationship between crop and its
climate. Thus, the complexities of plant processes in relation to its micro climate can be
resolved.
Climate Extremes
Crops can be protected from climatic extremities like floods, droughts, hail,
windstorms, etc. by forecasting them and warning the farmers in advance.

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Analysing Soil Moisture Stress
Climatic water balance method can be used to determine the soil moisture stress
and drought. Essential protective procedures, like irrigation, mulching, application of anti-
transparent, defoliation, thinning etc. can thus be undertaken to combat these situations.
Livestock Production
Livestock production is a part of agriculture. The production, growth and
development of livestock is affected by the weather conditions. The weather conditions
are studied in Agricultural Meteorology and breeds can be selected according to the
conditions or amiable conditions can be provided for existing breeds.
Soil Formation
Climate is a foremost factor in soil formation and development as the process of
soil formation depends on climatic variables like temperature, precipitation, humidity,
wind etc.
Need of Agrometeorolgoy
1. The crops are to be sown at the optimum period for maximum yield. In dry lands, the
time of receipt of rainfall decides the sowing date. Predicted on set of monsoon helps
in pre-monsoon sowing.
2. Study of agro-meteorology helps to minimise the crop losses due to excess rainfall,
cold/heat waves, cyclones etc.
3. It helps in forecasting pest and diseases, choice of crops, irrigation and other cultural
operations through short, medium and long range forecasts.
4. It helps to identify places with same climatic conditions (Agro-climatic zones). This
will enable to adopt suitable crop production practices based on the local climatic
conditions. It also helps in the introduction of new crops and varieties which are more
productive than the native crops and varieties.
5. It helps in the development of crop weather models which enables to predict crop
productivity under various climatic conditions.
6. It helps in the preparation of crop weather calendars for different locations.
7. It enables to issue crop weather bulletins to farmers.
8. It enables to forecast the crop yield based on weather to plan and manage food
production changes in a region.
9. To make the farmers more “Weather conscious” in planning their agricultural
operations.
Development of Agricultural Meteorology
Climatology is compounded of two Greek words, klima + logos; klima means slope of the
earth, and logos means a discourse or study. In brief, climatology may be defined as the
scientific study of climate. Climatology is at once an old and a new science premature
man was greatly affected by the phenomena of weather and climate and was unable to
explain logically. Superstition served to interpret atmospheric mysteries such as rain, wind
and lightening. In the early civilization, Gods were often assigned to the climatic elements,
Indians still hold ceremonial worships / dances to Gods to produce rains at times of
drought.
The Greek philosophers showed a great interest in meteorological science. In fact the
world “Meteorology” is of Greek origin, meaning, discourse or study on things about and

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included meteors and optical phenomena. In fact, the word “Meteorology has been
borrowed from Aristotle’s Meteorological” dated about 350 BC. The period of weather
lore and superstitions in the development of meteorology lasted until the beginning of the
17th Century when the invention of instruments for scientific analysis of weather
phenomena was made. In 1593, Galileo constructed a thermometer and in 1643, his
student Toricelli discovered the principles of mercurial Barometer. The climatological map
was published by British astronomer ‘Edmund Hally’ in 1686. By 1800, dependable
weather observations were made in Europe and USA.
An international Meteorological Organisation had been established in 1878. The world
meteorological organisation (WMO) took its present form in 1951. It serves as a
specialized agency to carry out the world wide exchange of meteorological information
with the headquarters in Geneva, Switzerland.
The India Meteorological Department (IMD) was established in the year 1875. The
division of Agricultural Meteorology was started by the IMD in 1932 to meet the needs of
agriculturist and researchers. The IMD has brought out many useful publications on
rainfall. The Rainfall Atlas of India was published based on the rainfall data from 1901 to
1950. In addition to rendering advice from time to time, the IMD began to offer a regular
weather service and farmers weather bulletins from 1945. The bulletins are broadcast daily
in 20 regional languages in all the All India Radio stations (DhoorDharhan also do this
service) on expected weather conditions during the next 36 hrs. Weather report is also
broadcasted through television.

Composition and structure of atmosphere

Stratification and Composition of Atmosphere
The atmosphere is a mechanical mixture of many gases, not a chemical compound. In
addition, it contains water vapor volume (4% of atmospheric composition) and huge
number of solid particles, called aerosols. Some of the gases (N2, O2, Ar) may be regarded
as permanent atmospheric components that remain in fixed proportions to the total gas
volume. Nitrogen and oxygen constitute about 99 percent of clean dry air. Other
constituents vary in quantity from place to place and from time to time. If the suspended
particles, water vapour and other variable gases were excluded from the atmosphere, we
would find that the dry air is very stable all over the earth up to an altitude of about 80
kilometres.
Properties of atmosphere
It is not visible, but felt if it is in motion. It has no smell or taste or colour. It occupies
space and has mass. It conducts sound and supports combustion. It exerts a pressure. It is
transparent or translucent and act as filter to almost all incoming solar radiation. It acts
opaque to long wave radiation emitted from the earth. It diffuses heat and gases. It is denser
over the earth surface and becomes thinner at high altitude Composition of the
atmosphere
Primary gases: The following are the principal gases comprising dry air in the lower
atmosphere (Below 25 km.), in percentage by volume approximately.
Nitrogen (N2) 78.08 Methane (CH4) 0.00017
Oxygen (O2) 20.95 Nitrous oxide (N2O) 0.00003

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* Argon (Ar) 0.93 Sulphur dioxide (SO2) Trace
Carbon dioxide (CO2) 0.037 * Krypton (Kr) Trace
* Neon (Ne) 0.0018 * Xenon (Xe) Trace
* Helium (He) 0.0005 Carbon monoxide (CO) Trace
Ozone (O3) 0.00006 Ammonia (NH3) Trace
Hydrogen (H) 0.00005 Iodine (I) Trace
*Inert chemically never found in any chemical compounds.
N2: Relatively chemically inactive. Main function is to regulate combustion by diluting
O2. Indirectly helps oxidation.
CO2: plants take CO2 in the processes of photosynthesis. It is efficient absorber of heat
from upper atmosphere as well as the earth and emits half of the absorbed heat back to
earth. Influences flow of energy through the atmosphere. The proportion remains same but
percent increases due to burning of fossil fuels. From 1890 to 1970 CO2 content has been
increased more than 10 times which warms the lower atmosphere leading to climatic
changes.
Ozone (O3): It is a type of oxygen molecule formed of three atoms rather than two. It is
found only in very small quantity in the upper atmosphere. It is less than 0.0006 per cent
by volume. The maximum concentrations of Ozone are found between about 30 and 60
km. Although it is formed at higher levels and transported downward. It is the most
efficient absorber of the burning ultraviolet radiation from the sun acts as a filter. Absence
of Ozone layer will make the earth’s surface unfit for human habitation and for all living
organisms.
N2O: deterioration of O3 occurred due to reactions involving nitrogen oxides and chlorine
in middle and upper stratosphere.
Of all the gases, oxygen happens to be the most important for it is essential to all living
organisms.
Moisture (Water vapour):
Water vapour is one of the most variable gases in the atmosphere, which is present in
small amounts, but is very important. The water vapour content of air may vary from 0.02
per cent by volume in a cold dry climate to nearly 4 per cent (about 3 percent by weight)
in the humid tropics and it is absent above 10 to 12 km from ground level. About 90 percent
water vapour lies in 6 km of atmosphere from ground because earth’s surface is the source
and only 1 percent above 10 to 12 km of atmosphere from earth surface. It is largely
derived from oceans through the evaporation of water. It is also derived through
evapotranspiration from soil, plants, vegetable and evaporation from rivers, canals, lakes,
ponds, surface, open well and various other water bodies. The variations in this percentage
over time and place are very important considerations climatically like CO2, water vapour
has insulating action of the atmosphere. It absorbs not only the long wave terrestrial
radiation, but also a part of the incoming solar radiation. Thus it regulates energy transfer
through the atmosphere. Water vapour is the source of all clouds and perceptions. It is an
important component of hydrological cycle. The capacity of air to hold moisture increases
with increase in temperature.
Aerosols or impurities (Dust particles):

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 It includes all solid and dust particles present suspended in the atmosphere. Many aerosols
are invisible to the naked eyes and are microscopic. These particles are sea salt from
breaking sea waves, pollens, fine seeds of plants, spores, bacteria, and various
microorganisms, smoke and black carbon from fires, tiny sand particles, volcanic ash and
meteoric dust, etc. Aerosols enter the atmosphere by urban and industrial pollution,
agricultural practices, forest fires, sea sprays, volcanic activities and wind raised dust. It
may contribute up to 30 percent of atmospheric air. Dust particles are a major contributory
factor in the formation of clouds and fogs. It is responsible for the red, orange colour of
the sky at sunrise and sunset. They absorb a part of incoming shortwave solar radiation.
Aerosol such as sulphate, soot, organic carbon and mineral dust, scatters sunlight back to
space and thereby cause a regional cooling effect. Some of the dust particles are
hygroscopic and act as nuclei of condensation, resulting in cloud formation and
precipitation.
Variable constituents: CO2, Water vapours, aerosols.
Non-variable Constituents: Gases like nitrogen, oxygen, ozone, argon etc
Layering of atmosphere
Atmosphere can be divided into two spheres on the bases of its compositions with
respect to height.
1) Homosphere 2) Heterosphere
Homosphere: In the lower region, up to the height of 80-90 km, various gases are
thoroughly mixed and are homogeneous due to the process of turbulent mixing and
diffusion. Composition of this sphere remains normally same. The proportions of the
component gases of the sphere are uniform at different levels.
Sub-divided into
a. Troposphere - Very shallow transition layer Tropopause
b. Stratosphere - Stratopause
c. Mesosphere - Mesopause
Heterosphere: The atmosphere above the homosphere is not uniform in composition. In
heterosphere gaseous composition changes and the various, gases form individually
separate layers with chemical and physical properties.
The lower portion of heterosphere
Oxygen and Nitrogen layer – 115 to 200 km above earth’s surface molecular N.
Atomic oxygen layer – 200-965 km.
Helium layer – 965-2400 km.
Hydrogen layer – 2400-10,000 km.
Distribution of the gases is governed by Earth’s gravitational force, thus heavier
gases sink downward, while lighter gases remain at higher altitude.
Extent of the atmosphere
There is no sharp boundary between the atmosphere and extra-terrestrial space. It
is difficult to ascertain the height of atmosphere. Its density becomes less and less with
altitude. Half of mass of atmosphere is up to 5.5 km from the ground surface. Average
density is 1.2 kg per m3 at surface and 0.7 kg per m3 at 5000 m. Air may exist up to 400
km in perceptible quantity. The weight of air on surface at sea level is about 10,000 kg per
m2. The weight of atmosphere is 5.6 x 1014 metric tonnes.

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Physical structure of atmosphere
On the basis of vertical temperature difference the atmosphere can be divided in to
four horizontal layers or shells.
1. Troposphere 2. Stratosphere 3. Mesosphere (Ozonosphere) 4. Thermosphere.
1. Troposphere: The lowest layer of atmosphere is called the troposphere. Altitude of this
layer changes according to latitude. This layer is thick (16 km) at equator while it is thin
(8 km) at poles. It contains 75 percent of gaseous mass, water vapors and aerosols. This
is the region where weather phenomena is very well marked and hence described as
weather making layer of atmosphere. Temperature decreases fairly uniform with
altitude until minimum temperature of -50 to -600C is reached. There is general decrease
of temperature with height at a minimum rate of about 6.50C per km. The temperature
decrease with increase in height is called as lapse rate. The top of troposphere where
the decrease of temperature with height ceases is tropopause. The average temperature
at tropopause over equator is -800C while -400C over poles. The height of tropopause
varies with season.
2. Stratosphere: It is second layer above troposphere up to 50 km contains about 10
percent of atmospheric mass and much of atmosphere ozone. The density of ozone is
highest at 22 km approx. Ozone at the upper layer absorbs the ultraviolet rays from the
sun. The ultraviolet rays are quite detrimental to living things on the globe of earth.
Stratosphere acts as a protective layer which absorbs ultraviolet rays. This layer is
thicker at poles. The air density is much lower in stratosphere even though temperature
rises with height due to limited absorption of ultraviolet solar radiation by ozone in
summer. There are marked complex seasonal changes in winter and may found low
temperatures at equator and in middle stratosphere at high altitude. The events in this
layer are linked with temperature and circulation changes in the troposphere. A layer at
height of 50 km where maximum temperature was observed due to absorption of
ultraviolet solar radiation by ozone and which separates stratosphere to mesosphere is
called as stratopause.
3. Mesosphere (Ozonosphere): The temperature of this layer decreases to a minimum of
about -900C at about 80 km. Above 80 km the temperature again begins to rise with rise
with height (temperature inversion) and thin isothermal layer which separates
mesosphere from thermosphere is mesopause. Molecular oxygen and ozone layers
absorb solar radiation to increase temperature around 85 km height. Most meteors bun
and disintegrate in this layer, due to which temperature of the layer is increased. Due to
meteoric dust particles noctilucent clouds are observed in summer nights in this region
on high altitude.
4. Thermosphere: Above the mesopause the atmosphere densities are extremely low. The
lower portion of the atmosphere is composed mainly of nitrogen and oxygen in
molecular form (N2& O2) and atomic oxygen (O), whereas above 200 km atomic
oxygen predominant over nitrogen and oxygen. Temperature increases with height
due to absorption of extreme ultraviolet radiation by molecular and atomic oxygen and
reaches to bout 9500C at 350 km. But it is essentially a theoretical because artificial
satellites do not gain such temperature because of rarefied air.

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5. Exosphere and magnetosphere: It is present between 500 km to 750 km. Here atoms
of oxygen, hydrogen and helium form the tenuous atmosphere. Neutral helium and
hydrogen atoms, which have low atomic weights, can escape into space since the chance
of molecular collisions which helps in deflect them downward are less with increase in
height. Hydrogen is replaced by methane due to the breakdown of water vapour near
mesopause. Helium is produced due to action of cosmic radiation on nitrogen and from
the slow and steady breakdown of radioactive elements in the earth crust. One percent
ionized particle is found in exosphere up to 200 km height from ground hence it is also
called as ionosphere. In the magnetosphere i.e. beyond about 200 km only electrons
(negative) and protons (positive) derived from the solar winds are observed and this act
as plasma of electrically conducting gas. Kinetic temperature may reach 5568oC in this
sphere.

Layers of
Main layers separation
1. Troposphere
Tropopause
2. Stratosphere
3. Mesosphere
4. Thermosphere

Stratopause

5. Exosphere and magnetosphere Mesopause

Definition of weather and climate, aspects involved in weather and climate

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Weather: Weather is the condition and behaviour of the atmosphere at given time and
place. or
Physical condition or state of the atmosphere at a given time and place.
The physical condition of atmosphere can be described by using numerical values
of the six basic atmospheric factors, which are known as weather elements or weather
parameters.
1. Air temperature 2. Atmospheric Pressure
3. Wind 4. Humidity
5. Sunshine 6. Clouds and precipitation
Visibility, radiation and evaporation, pollution may be added in the list, of weather
parameters.
Out of the weather parameters temperature and precipitation are most important.
Climate: Is defined as generalized or average weather of a place or a region.
It is a longer phase of the weather. The climate can be described by taking
statistical averages of weather elements over period like, week, fortnight, month or season.
For complete description of climate the highest and lowest values of weather elements
during the period under consideration are essentially required to be known for the given
place or region.
The values of weather elements averaged over a period like 10 years or more are known
as normal.
Agroclimatic regions: The grouping of different physical areas within the country into
broadly homogeneous zones based on climatic and edaphic factors.
Distinction between weather and climate
Weather Climate
1. It is an instantaneous physical 1. Climate is a generalized weather over an condition
of the atmosphere at a area. location.
2. Weather is dynamic and changes 2. Climate change requires a longer period within
short time like few hours like 5-10 years.
3. Weather of two places having 3. Climate of two places having same same numerical
values is said to statistical averages of weather elements be same cannot be same
because their distribution over the period may be different.
4. Weather can be categorized as fair, 4. Climates are categorized as desert, settled, fine,
excellent etc. marine, continental climate etc.
5. Weather of individual season 5. Climate conditions of a region decide
the decides the crop yield in that type of the crop, variety suitable for that
particular season region.
6. Weather influences contingency 6. Climate is considered for long term planning of
crops during a season. planning in agriculture.
ClimateTime Scale
Weather systems and atmospheric motions differ in size and life span. Following time
scales are normally used to study these phenomena.
Name of the scale Time span Horizontal Spread Examples
A) Macro scale

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 General circulation
i. Planetary Scale Weeks to year 5000-10000 km
waves in westerly.
Cyclones, Anticyclones,
ii. Synoptic scale Days to Weeks 100-5000 km
Hurricanes.
Thunder storms, land
B) Mesoscale Minutes to days 1-100 km and sea breeze,
Tornadoes.
Turbulence, eddies,
Seconds to processes operating
C) Micro-Scale < 1 km
minutes with vegetation,
canopies.
Elements of weather and climate Introduction:
The climate of a region is ultimately determined by the radiation energy of the sun
and its distribution and temporal fluctuations. The long-term state of the atmosphere is a
function of a variety of interacting elements. They are Solar radiation, Air masses, Pressure
systems (and cyclone belts), Ocean Currents, Topography.
1. Solar radiation: Solar radiation is the radiation or energy we get from the sun. It is also
known as short-wave radiation (Broadly includes visible, near ultraviolet and near
infrared radiation in wave length of 0.1µm to 5.0 µm). Solar radiation is probably the
most important element of climate. Solar radiation first and foremost, heats the Earth's
surface which in turn determines the temperature of the air above. The receipt of solar
radiation drives evaporation, so long as there is water available. Heating of the air
determines its stability, which affects cloud development and precipitation. Unequal
heating of the Earth's surface creates pressure gradients that result in wind. Every
location on Earth receives sunlight at least part of the year.
The amount of solar radiation that reaches any one spot on the Earth's surface varies
according to Geographic location, Time of day, Season, Local landscape, Local
weather.
Solar radiation comes in many forms, such as visible light, radio waves, heat
(infrared), x-rays, and ultraviolet rays.
Measurements for solar radiation are higher on clear, sunny day and usually low on
cloudy days. When the sun is down, or there are heavy clouds blocking the sun, solar
radiation is measured at zero.
2. Temperature: Temperature is a very important factor in determining the weather,
because it influences or controls other elements of the weather, such as precipitation,
humidity, clouds and atmospheric pressure.
3. Air masses-wind and storms:
Air masses: An air mass is a large body of air with generally uniform temperature and
humidity. Air masses control the characteristics of temperature, humidity, and stability.
Location relative to source regions of air masses in part determines the variation of
the day-to-day weather and long-term climate of a place.
Winds: The horizontal movement of the atmosphere is called wind. Wind can be felt
only when it is in motion. Wind is the result of the horizontal differences in the air
pressure. Wind is simply the movement of air from high pressure to low pressure. The
speed of the wind is determined by the difference between the high and low pressure.

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 The greater the difference the faster the wind speed. Closer the isobars stronger are
the winds. The wind brings with it the temperature of the area from it is coming,
therefore a high pressure in a warm region will make the temperature higher in the
low pressure area. Wind-chill is the effect of the wind making it feel colder than it
actually is. As the wind speed increases air is moving more quickly and therefore
removes warm air therefore making it seem colder than the actual temperature.
4. Pressure systems: Air pressure is the weight of air resting on the earth's surface. Air
has specific weight. This weight exerted by the air on the earth's surface is atmospheric
pressure. It is defined as the force per unit area exerted against a surface by the weight
of air above that surface in the Earth's atmosphere. Pressure systems have a direct
impact on the precipitation. In general, places dominated by low pressure tend to be
moist, while those dominated by high pressure are dry. The seasonality of precipitation
is affected by the seasonal movement of global and regional pressure systems.
5. Ocean Currents: Ocean currents greatly affect the temperature and precipitation of a
climate. Those climates bordering cold currents tend to be drier as the cold ocean water
helps stabilize the air and inhibit cloud formation and precipitation. Air travelling over
cold ocean currents lose energy to the water and thus moderate the temperature of
nearby coastal locations. Air masses travelling over warm ocean currents promote
instability and precipitation. Additionally, the warm ocean water keeps air temperatures
somewhat warmer than locations just inland from the coast during the winter.
6. Topography: Topography affects climate in a variety of ways. The orientation of
mountains to the prevailing wind affects precipitation. Windward slopes, those facing
into the wind, experience more precipitation due to orographic uplift of the air. Leeward
sides of mountains are in the rain shadow and thus receive less precipitation. Air
temperatures are affected by slope and orientation as slopes facing into the Sun will be
warmer than those facing away. Temperature also decreases as one moves toward higher
elevations.
7. Humidity: Atmospheric moisture is the most important element of the atmosphere
which modifies the air temperature. Humidity is the measurable amount of moisture in
the air of the lower atmosphere. There are three types of humidity:-
a) Absolute humidity: The total amount of water vapour present in per volume of air at
a definite temperature.
b) Relative humidity: is the ratio of the water vapours present in air having a definite
volume at a specific temperature compared to the maximum water vapours that the air
is able to hold without condensing at that given temperature.
c) Specific humidity: is defined as the mass of water vapour in grams contained in a
kilogram of air and it represents the actual quantity of moisture present in a definite air.
The humidity element of weather makes the day feels hotter and can be used to
predict coming storms. The humidity element of climate is the prolonged moisture
level of an area that can affect entire ecosystems.
8. Precipitation: Precipitation is the term given to moisture that falls from the air to the
ground. Precipitation includes snow, hail, sleet, drizzle, fog, mist and rain.
Precipitation is simply any water form that falls to the Earth from overhead cloud
formations. As an element of weather, precipitation determines whether outdoor

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 activities are suitable or if the water levels of lakes and rivers will rise. As an element
of climate, precipitation is a long-term, predictable factor of a region's makeup. For
instance, a desert may experience a storm (weather) though it remains a typically dry
area (climate).
9. Cloudiness: Clouds are suspended water in the atmosphere. Clouds are usually the
most obvious feature of the sky. Clouds give us a clue about what is going on in our
atmosphere and how the weather might change in the hours or even days to come.
Each type of cloud forms in a different way and each brings its own kind of weather.
Clouds play multiple critical roles in the climate system. In particular, being bright
objects in the visible part of the solar spectrum, they efficiently reflect light to space
and thus contribute to the cooling of the planet. A small increase in cloud cover could,
in principle, balance the heating resulting from greenhouse gases. Clouds are the base
for precipitation. In summer cloudy days provide protection from the rays of the sun.
In winter cloudy skies at night diminish nocturnal radiation and check the fall of
temperature. A clear calm winter night are usually the coldest and helps in
condensation.
10. Visibility: The most critical weather element. Obstructions to visibility include
clouds, fog, smoke, haze, and precipitation. It is represented by the meteorological
optical range (MOR) and varies with the background illumination. In extremely clean
air in Arctic or mountainous areas, the visibility can be up to 70 kilometres to 100
kilometres. Visibility is often reduced somewhat by air pollution and high humidity.
Fog and smoke can reduce visibility to near zero, making driving extremely
dangerous. The same can happen in a sandstorm in and near desert areas, or with forest
fires. Heavy rain (such as from a thunderstorm) not only causes low visibility, but the
inability to brake quickly due to hydroplaning. Blizzards and ground blizzards
(blowing snow) are also defined in part by low visibility.
Factors affecting weather elements:
Following factors affects the weather elements.
1) Latitude: It is defined as an angular distance of a place towards the North and South
form equator. Higher the latitude, lesser is the receipt of solar radiations resulting in
colder climate and vice versa.
2) Altitude: Means height of a place above mean sea level. Pressure and temperature
decreases with increase in altitude, although receipt of solar radiation may increase.
Since the density of air is less at higher attitude the absorbing capacity of air is
relatively less with reference to earth’s long wave radiation. This explains why the
surface air temperature at higher altitude is relatively low though it is relatively nearer
to the sun’s rays.
3) Topography: The term indicates the land surface is plane or uneven. On even
topography the wind speed is higher than the land with uneven topography. Wind is the
carrier of heat and water vapours from one place to another.
4) Mountains: Influences the climate by interfering the free flow of air currents and
interfering the rainfall and temperature e.g. Sahyadri ranges. Lot of rain is received
towards windward side and develops a rain shadow area towards leeward side.

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5) Nearness to sea: Distance of a place from sea affects temperature and humidity
conditions of area. Water is slower to warm up and slower to cool, creating a
moderating effect on temperature near coastal area; humidity remains high near the
sea. The daily range of surface air temperature is less in coastal area when compared
to inland. The sea breezes during the daytime as well as land breeze in nights are
common phenomena in summer along the coastal regions.
6) Ocean currents: Ocean currents carry tropical temperature towards temperate areas,
and cold waters toward tropical sea, thus changing the local climate.
7) Water bodies: Large water bodies like lakes, reservoirs etc. develops local breeze, and
also affects the temperature and humidity conditions of place similarly rainfall is also
increased in the nearby area.
8) Snow and ice cover: Snow – flakes of frozen water. Snow on the earth surface reflects
the solar radiation efficiently therefore the temperature of atmosphere is increased by
absorbing these reflected radiations. Similarly snow cover is bad conductor of heat
therefore the soil temperature is also maintained which saves the soil life/microbes.
9) Vegetation: In dense vegetation the atmospheric humidity is higher due to lot of
transpiration. Solar radiation receipts are less, due to foliage interception. Wind
velocity is less because of interruption of trees. Rainfall is usually higher in these
localities.
10) Permanent wind direction: It affects the temperature and humidity of a place as per
weather conditions at windward side of permanent wind direction.

Solar radiation
The sun is the primary source of heat to the earth and its atmosphere. The sun behaves
virtually as a black body i.e. it absorbs all energy received and radiates energy at
maximum possible rate at present temperature. The average distance that separates the
earth from the sun is about 149.6 million km. The diameter of the sun measures roughly
about 1.3824 million km. The surface temperature of the sun is estimated between 5500oC
and 6100oC (5762oK). Solar energy is originated from nuclear reaction within the suns hot
core with a temperature of 8×106 to 40×1006oK and transmitted to surface by radiation and
hydrogen convection. Visible solar radiation (light) comes from cool outer surface called
photosphere. The out flow of hot gases (plasma) from sun referred as solar wind with a
speed of 1.5 ×106 km per hr interacts with earth’s magnetic field and upper atmosphere.
Solar radiation provides more than 99.9 percent of the energy that heats the earth. The
heat received form, other outer space bodies as well as the interior of the earth is rather too
insignificant to draw attention. Undoubtedly, the radiant energy from the sun is the most
important control of our weather and climate. The most surprising fact about the incoming
solar radiation (insolation) that strikes the earth's surface is that it is equal to about 23
billion horse power. Actually it is this amount of energy received from the sun that acts as
the driving force for all the atmospheric as well as biological processes on the earth.
Besides, all other sources of energy found on earth such as coal, oil and wood etc. are
nothing but converted form of solar energy.

Definition

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 Solar radiation is defined as, the flux of the radiant energy from the sun.
All matter having temperature above the absolute zero, pass on energy to the surrounding
space. This energy is converted by green plants in process of photosynthesis into the
potential energy of organic material.
Importance of solar radiation for plants:
1. From germination of seed to harvesting and even post-harvest processes are influenced
by solar radiation.
2. Solar radiation provides energy for
a. All the phenomenon related to biomass production.
b. All photosynthetic processes.
c. All physical processes taking place in the soil, plant and their environment
3. Solar radiation controls the distribution of temperature thereby distribution of crops into
different regions.
Processes of Heat Energy Transfer:
Radiation: Radiation is the process of transmission of thermal energy in the form of
Electromagnetic waves from one place to another even through vacuum with the speed of
light and is the means by which energy emitted by the sun reaches the earth.
Every material and biological body in our vicinity i.e. soil, water, plants, animals, etc.
with temperature greater than absolute zero emits characteristic radiation specific to its
own body temperature. Thus all bodies are in interaction with other bodies through
radiation process.
Conduction: Conduction is the process of heat transfer through matter by molecular
activity. In this process heat is transferred from one part of a body to another or between
two objects touching each other. Conduction occurs through molecular movement.
Convection: Convection is the process of the transfer of heat, through movement of a
mass or substance from one place to another. Convention is possible only in gases or fluids,
for they alone have internal mass motions. In solid substances this type of heat transfer is
impossible.
Insolation:
The word 'insolation' is contraction of "incoming solar radiation". Radiant energy from
the sun that strikes the earth is called insolation. Incoming solar radiation or energy
received on the surface of earth from sun is known as insolation. Intensity of radiation
(radiant flux density) is the amount of radiant energy received on unit area of surface,
which held perpendicular to the solar beam in unit time. It depends upon the amount of
solar radiation reaching the outer limits of the atmosphere, transparency of the atmosphere,
day length and the angle at which noon rays strike the earth. In morning and evening the
light intensity is less because of inclined angle of sun rays which travels more distance and
covers more area on earth surface which leads to lowering in temperature. That’s why
higher temperature is noticed over tropics and lower temperature over the higher latitude.
A part of the incoming radiation on surface is absorbed, while a part is reflected and
remaining is transmitted. All three i.e. absorptivity, reflectivity and transmittivity becomes
unity for any given amount of incident radiation on given surface.
Absorptivity: Absorptivity of any object is defined as the ratio of the electromagnetic
radiant power absorbed to the total amount of radiation incident upon the same object.

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The absorptivity of black body is one. Natural bodies like sun and the earth are nearly
perfect black bodies.
Reflectivity: It is defined as the ratio of the monochromatic beam of electromagnetic
radiation reflected by a body to that of total incident upon it. If it is express in percentage
then it becomes albedo. All white surfaces reflect the maximum while it is less in black
surface. In case of snow it varies from 70 to 90 percent depending upon the freshness while
it is only 10 percent in case of forest and 20 percent in bare soils.
Transmittivity: This is the ratio transmitted to the incident radiation on a surface
preferably a crop canopy.
Emittance (emissivity): It is a ratio of the emitted radiation of a given surface at a
specified wavelength to the emittance of an ideal black body at the same wave length and
temperature.
For other than a black body the value of emittance is always less than one and for black
body the emittance value is one.
Black body:
It is an ideal hypothetical body which absorbs all the electromagnetic radiation falling on
it. It neither reflects nor transmits any radiation striking it. However, when heated, it emits
all the possible wavelengths of solar radiation and becomes a perfect radiator. In nature the
sun and the earth are nearly perfect black bodies.
Solar spectrum:
The sun emits radiant energy in the form of electromagnetic waves. Solar radiation from
the sun is spread over broad band consists of a bundle of rays of radiant energy of different
wave lengths known as solar spectrum. The visible portion of the solar spectrum (0.4 to
0.76 µm) appears as light which is 41 percent. Light travels with a speed of 2,97,600 km
per sec. It takes 20 second to 8 minutes to reach the earth. Light is the total effect of the
combination of the seven different colours, namely red, orange, yellow, green, blue, indigo
and violet (VIBGYOR). The waves that produce the effect of red colour are the longest
and those producing the violet are the shortest. Waves shorter than the violet are called
ultraviolet rays, while those longer than the red are known as infrared rays. The ultra violet
(0.2 to 0.4 m) waves form only 7 per cent of the insolation, but have strong photochemical
effects on some substances. The infra-red rays (>0.7 µm), even though invisible, form 52
per cent of the insolation. They are largely absorbed by water vapour that is concentrated
in the lower atmosphere.
1 µm = 1 micrometer = 10-6 m

Different bands of solar spectrum:

1. The band of solar spectrum having shorter wavelength ranges between 0.015 to 0.4 µm
are known as ultra-violet rays (U.V. rays) these are chemically very active and capable
of destroying all forms of life. These are naturally filtered in the atmosphere which
avoids a danger for life on the earth.
2. The part of the spectrum which is visible is known as light. It is the part of the spectrum
which is essential for all plant processes and wavelength ranges from 0.4 to 0.76µm.

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3. The third part of solar spectrum is known as infrared band. This is essential for thermal
energy of the plant (Source of heat to the plant). This band is having wavelength >
0.76µm.
Basic radiation terminology:
1. Short wave radiation: This is a part of solar spectrum having wavelength less than 0.4
µm.
2. Long wave radiation: The terrestrial and atmospheric radiation which are in the
wavelengths between 0.4 and 12 µm.
3. Net radiation: The difference between the incoming radiation from the sun and
outgoing solar radiation from the earth is known as net radiation.
4. Solar constant: The sun is the source of more than 99 per cent of the thermal energy
required for the physical processes taking place in the earth atmosphere system. Every
minute, the sun radiates approximately 56 x 1026 calories of energy.
In terms of the energy per unit area incident on a spherical shell with a radius of 1.5 x 1013
cm (the mean distance of the earth from the sun) and concentric with the sun, this energy
is equal to
56 x 1026 cal. min-1
S = --------------------------------- = 2.0 Langley (cal/cm2) min-1.
4 (1.5 x 1013 cm)2

(Langley = gram calories cm-2).

The solar constant (S) is a true constant, but fluctuates by as much as ± 3.5 percent
about its mean value, depending upon the distance of earth from the sun.
Solar constant is defined as the rate at which solar radiation is received outside the earth's
atmosphere on a surface perpendicular to the sun's rays when the earth is at an average
distance from the sun.
The Smithsonian Institute, USA has come to the conclusion that the standard value of
solar constant is 1.94 gram calories per cm2 per minute.
Since there is fluctuation in the amount of radiant energy emitted by the sun due to
periodic disturbances on the solar surface, the amount of solar constant, therefore, registers
a slight increase or decrease. However, this variation hardly exceeds 2-3 per cent.
The amount of insolation received on any date at any place on the earth is governed
by
i) The solar constant which depends on (a) energy output of the sun and (b)
distance from the earth to sun. ii) Transparency of the atmosphere.
iii) Duration of the daily sunlight period.
iv) Angle at which the sun's rays strike the earth.
The distance between the earth and the sun varies between 94.5 million miles
(152.1 million km) at aphelion (July 4th) and 91.5 million miles (147.3 million km) at
perihelion (January 5th). The amount of radiation received is 7 percent greater at perihelion
than at aphelion. This is a consequence of the increase sequence law which states, in effect,
that the radiation received on any unit area decreases in proportion to the square of the
distance to the sources.

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 A transparency of the atmosphere has a more important bearing upon the amount
of insolation which reaches the earth's surface. The areas having heavy dust, clouds, water
vapour and cloudiness or polluted air will receive less direct insolation. The transparency
of atmosphere depends on the latitude of a place. At middle and high latitudes the sun's
rays must pass through thicker layers of reflecting or scattering material and it is not so at
tropical latitudes.
Aphelion: The point farthest from the sun in the obit of a planet.
Perihelion: The point nearest from the sun in the orbit of a planet.
The estimated value of solar constant varies from 1.94 to 5.01 Langley per min.
The average value is 2 Langley per min.
Importance of Light
1. Chlorophyll formation: Light is one of the important and essential factors
responsible for chlorophyll in plants. Without light plants become pale yellow and have
long thin internodes, a condition known as 'etiolating.' Chlorophyll decomposes in bright
sun light; thus formation and decomposition both go on simultaneously when the plant is
exposed to light.
2. Functioning of stomata: Light is an important factor influencing the daily opening
and closing of stomata, which in turn, affect respiration and photosynthesis.
3. Photosynthesis: Light is the most important factor of locality for photosynthesis as
it cannot take place in darkness. Out of the seven colours in visible part of the spectrum,
only red and blue are effective in photosynthesis. It has been estimated that light used in
photosynthesis is less than 2 percent of the light energy incident on well-illuminated
leaves.
4. Growth: Light influence the growth of plants and trees through its effect on
photosynthesis. The influence of light varies with its quality, duration and intensity.
Quality of light refers to colours. Plant growth in blue light is small. Red light on other
hand results in elongation of cells giving the appearance of etiolated plants. Violet and
ultraviolet light bring about dwarfing effect.
5. Form and quality of trees: The elongation of the growing axes of tree in the forest
occurs mainly between sunset and sunrise because the low intensities of light and infrared
radiation tend to stimulate height growth. Even the form of trees growing in shade is very
dissimilar to that of trees growing in the open.
6. Species stratification and size and structure of leaves: The intensity of light in the
forest varies from place to place and from time to time between wide limits.
Effect of light on plants
Solar radiation in the primary Electromagnetic spectrum showing the wavelength of
different type of radiations is shown below.
Type of radiation wavelength
1. Gamma rays : < 0.01 nm
2. X rays : 0.01 to 10 nm
3. U.V. : 10 nm to 390 nm
4. Visible : 390 – 760 nm
5. Infrared : 760 – 1 nm
6. microwaves : 1nm to 30 cm

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 7. Radio wave : > 30 cm
1 nm = 10-9 m
The shorter wave length in the solar spectrum is harmful to the plants when exposed
to excessive amounts. The atmosphere, however, absorbs almost all the shorter wave
lengths. The infrared radiation has thermal effect on plants by supplying necessary energy
for evaporation of water from the plants. Visible solar radiation is called as light.
Light is one of the important climatic factors for many vital functions of the plant.
It is essential for the synthesis of the most important pigment i.e. chlorophyll. The
chlorophyll absorbs the radiant energy and converts into potential energy of carbohydrates
(Photosynthesis). The carbohydrate thus formed is the connecting link between solar
energy and living world. In addition, it regulates the important physiological functions like
transpiration.
Effect of light on plants can be studied under four headings (i) Light intensity (ii)
Quality of light (iii) Duration of light and (iv) Direction of light.
Light Intensity:
The intensity of light is measured by a standard unit called candle. The amount of light
received at a distance of one meter from a standard candle is known as "Metre Candle or
Lux". The light intensity at one foot from a standard candle is called "foot candle" or
10.764 lux and the instrument used is called as "Lux meter". About one per cent of the
light energy is converted into biochemical energy. Very low light intensity reduces the rate
of photosynthesis and may even result in the closing of the stomata detrimental to plants
in many ways. This results in reduced plant growth. Very high light intensity increases the
rate of respiration. It causes rapid loss of water i.e. it increases the transpiration rate of
water from the plants resulting in closure of stomata. The most harmful effect of high
intensity light is that it oxidise the cell contents which is termed as "Solarisation". This
oxidation is different from respiration and is called as 'Photooxidation".
Under natural conditions light intensity varies greatly and plants show marked response
to changes of light intensities. Based on the response to light intensities the plants are
classified as follows:
i) Sciophytes(shade loving plants): The plants that grow better under partially shade
(low light) conditions e.g., betel vines, buckwheat, turmeric etc., ii) Halophytes (sun
loving Plants): Many species of plants produce maximum dry matter under high light
intensities when the moisture is available at the optimum level e.g. maize, sorghum, rice
etc. Except under glass house or shaded conditions, intensity of light cannot be controlled.
Quality of Light: when a beam of white light is passed through a prism, it is dispersed
into different colours with their wave lengths. This is called the visible part of the solar
spectrum. The different colours and their wave length are as follows.
Violet and Indigo 400 - 435 mm
Blue 435 - 490 mm
Green 490 - 574 mm
Yellow 574 - 595 mm
Orange 595 - 626 mm
Red 626 - 750 mm

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Visible rays 390 – 760 micron µ, mm
1 1
Micron = -------------- meter = --------------mm
1000000 1000
The principal wave lengths absorbed and used in photosynthesis are in the violetblue and
the orange-red regions. Among this for plant growth red light is the most favourable light
for growth followed by violet-blue. Ultra violet and shorter wave lengths are useful to kill
bacteria and many fungi.
Blue Light (↓↑ 440-510 nm)
Blue light is essential at the beginning of a plant’s growth cycle as this is the type light that
plants first absorb to help with chlorophyll production. Plants need lots of blue light during
the seeding process and right through the first part of their growth cycle to ensure healthy
roots, strong stems, and healthy leaves. Without blue light plants will never get out of the
ground, so any lighting system that together should include a healthy dose of exposure to
this type of light.
Green Light (↓↑ 515-555 nm)
While there has been some debate recently on the merits of green light during a plant’s
growth cycle there’s good reason plants normally have green lives – that’s because they
are least effective at absorbing this type of light. In general, plants use less of the green
light they absorb than any other part of the spectrum and that’s why plants appear green,
but that light is retained by the plants for photosynthesis; leaving this part of the spectrum
out altogether can negatively affect the growth of the plants.
Yellow and white Light (↓↑ 565-595 nm)
Yellow light isn’t the most effective part of the spectrum for plant growth, but it is still
present in sunlight and so it’s still important to ask the question of how plants use yellow
light during the process of photosynthesis. This is certainly debatable, but what is certain
is that yellow light is one of the least effective parts of the spectrum during your plants
growth cycle. It might seem intuitive to assume that yellow and white light are close to
each other on the spectrum, but that’s not the case at all. White light is actually made by
combining other colors on the spectrum such as red, green, and blue. Therefore white light
will actually be much more beneficial for the photosynthesis process than yellow light.
Red Light (↓↑ 620-690 nm)4 and Edge or dark red (↓↑ 690-740 nm)
Red light has longer wave lengths than blue light and is therefore a lot less energetic. It’s
important that plants are exposed to red light during the blooming or flowering stages, but
this type of light is not essential during the vegetative stage of plants growth in fact use of
only red light during the initial stages of plants growth cycle willhave negative results. It’s
best to use red light towards the end of the growth cycle in combination with some blue
light as well.
A full spectrum of Light/NIR-1 (↓↑ 780-900 nm)and NIR-2 (↓↑ 930-960 nm)
For the heal theist plants really need light from right across the color spectrum. It’s true
that certain types of light may be more effective at different stages of the growth cycle,
plants still need light from across the spectrum at any stage of their growth.
The Principal wave lengths absorbed and used in photosynthesis are in the violetblue and
the orange - red regions. Among this for plant growth red light is the most favourable light

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for growth followed by violet-blue. Ultra violet and shorter wave lengths are useful to kill
bacteria and many fungi.
Duration of light:
The duration of light has greater influence than the intensity. It has a considerable
importance in the selection of crop varieties. The response of plants to the relative length
of the day and night is known as photoperiodism. The plants are classified based on the
extent of response to day length as follows.
1. Long day plants: The plants which develop and produce normally when the
photoperiod is greater than the critical minimum (greater than 12 hours) e.g. cereals,
potato, sugar beet, wheat, barley etc.
2. Short day plants: The plants which develop normally when the photoperiod is less
than the critical maximum (less than 12 hours) e.g. tobacco, soybean, millets, maize,
sugarcane, etc.
3. Indeterminate or day neutral plants: Those plants which are not affected by photo
period e.g. tomato, cotton, sweet potato, pineapple etc.
The photoperiodism influences the plant characters such as floral initiation and
development of bulb and rhizome production, etc. If a long day plant is grown during
periods of short days the growth of internodes are shortened and flowering is delayed till
the long days come in the season. Similarly when short day plants are subjected to long
day periods, there will be abnormal vegetative growth and there may not be any floral
initiation. But many crops have photo insensitive varieties now days.
Direction of light: The direction of sunlight has a greater effect on the orientation of roots
shoots and leaves. In temperate regions, the southern slopes show better growth of plants
than the northern slopes due to higher contribution of sunlight in the southern side.
Orientation of leaves: The change of position or orientation of organs of plants caused by
light is usually called as "Phototropisum". For e.g. the leaves are oriented at right angles
to incidence of light to receive maximum radiation.
Photomorphogenesis: Change in the morphology of plants due to light. This is mainly
due to ultra violet and violet rays of the sun.
Instruments used for measuring solar radiation
1. Bellanispyranometer measures global solar radiation
2. Sunshine recorder measures bright sunshine hours in a day
3. Line quantum sensor measures photo synthetically active radiation
4. Photometer measures the light intensity
5. Lux meter measures the light intensity
6. Radiometer measures difference between income and outgoing radiation

Duration of daily sunlight period (Length of day)

The vertical rays of the sun at noon day fall directly overhead at the equator on
March 21st and this is called ‘vernal equinox’. The vertical rays continue to move
northward to the tropic of cancer and are overhead there on June 22nd and this date is
known as ‘summer solstice’ (in Northern hemisphere). Afterwards the rays return to the
equator on September 23rd and this date is known as ‘autumnal equinox’. Then it reaches

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the Tropic of Capricorn on December 22nd and this date is known as ‘winter solstice’ (In
Northern hemisphere). The summer and winter solstices will be reverse in the southern
hemisphere. At equinox days and nights are of equal length throughout the world. In
summer solstice the day will be longer and in winter solstice the day will be shorter than
night. The northern pole will be in day light for the full 24 hours on summer solstice and
will be dark for full 24 hours on winter solstice of Northern Hemisphere.
Angle of the sun rays:
The effect of varying angle at which the sun rays strike the earth can be seen daily
by the movement of the sun across the sky. At solar noon the intensity of insolation is the
greatest but in the morning and evening hours when the sun is at low angle, the amount
of insolation is also small.
At equator the angle of incidence varies from 23 ½o north of the zenith to 23 ½o
south of the zenith. The intensity of solar radiation ranges from 92 percent on June 22nd
and December 22nd and 100 percent on March 21st and September 23rd.
At 45oN latitude the angle of incidence varies from 21½o south of zenith to 68½o south or
only 21½o above the horizon. The variation in intensity due only to the change in the angle
of incidence is from 92 percent of maximum on June 22nd to 38 percent on December 22nd.

Factors affecting the solar radiation receipt on the Earth surface

The amount of solar energy received on the earth is affected by following factors.
I. Astronomical factors:
1. Solar output: The sun behaves as a black body and therefore the energy radiated
by the sun depends on its temperature.
2. Distance between the earth and the sun: The distance of the earth from the sun
changes due peculiarity of the earth’s orbit around the sun and consequently, the energy
received by the surface of earth also changes which bring seasonal changes.
II. Geographical factors:
1. Effect of atmosphere: The quantity of solar radiation passing to the earth is
depleted due to presence of aerosols. Similarly clouds also scatter, reflect and absorb solar
radiation. So the amount of radiations reaching the earth is affected.
2. Effect of latitude: According to latitude the amount of solar energy reaching the
earth changes because the day length and distance traveled by inclined sunrays through the
atmosphere changes.
3. Effect of aspect of altitude: The flux of solar radiations received increase with
increase in altitude. A mountain area which faces sunrays receives more radiation while
the valley floor may receive fewer amounts.
4. Length of day: As duration of day increases the amount of radiation also increases.
The intensity and day duration together decide the quantity of radiation receipt.
Greenhouse effect
Carbon dioxide, water vapour, methane, carbon monoxide, sulphur, nitrous oxide,
chlorofluorocarbons and chlorofluoromethanes are atmospheric constituents of major
importance in green hose effect. Incoming short wave radiation is not absorbed by above
atmospheric constituents but outgoing long wave radiation reemitted by earth surface is

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absorbed by them and reradiated back to earth surface. In this process, temperature of earth
get rise and earth warms up. It is known as greenhouse effect.
Heat Budget:
Out of total solar radiation reaches the outer limit of the atmosphere, about 23 percent is
reflected by clouds and scattered back to space by suspended particles and it is not used to
heat the air. The earth surface reflects 8 percent of radiation to the space. The total
reflectivity is known as earth's "albedo". The average albedo value for the earth is 31
percent. About 19 percent of solar radiation is absorbed by gases and water vapour, about
21 percent is absorbed the earth from scattering of clouds and atmosphere. Thus
approximately two-thirds of the total radiation is effective in heating the earth.
Albedo: It is the capacity of any surface to reflect the incoming radiation (light).
It is the ratio of incoming radiation to the outgoing radiation.
It is the ratio between the reflected radiations to the incident radiation on a crop field,
snow, leaves etc. for white bodies the albedo values are high.
The total reflectivity is known as earth's albedo. Average albedo value for earth is 31
percent. The total energy coming to the earth over a considerable period of time is equal
to the total outward losses. If this were not so, the earth would see become either very hot
or very cold. Actually there is a deficit of heat at higher latitudes and surplus in low
latitudes.
Albedo:
For fresh snow cover – 75 to 95
Cropped field – 12 to13
Dark cultivated soil – 7 to 10
Human skin – 15 to 25

Radiation budget of the earth atmosphere or heat balance:

Incoming radiations 100 units or 100 percent.
20% Energy is reflected from clouds and dust particles.
3% Scattered by gas molecules
8% Reflected by earth surface

Total - 31% Loss of energy

Out of remaining 69 percent of solar energy 19 percent absorbed by CO2, dust, water
vapour and remaining 49 percent earth, (28 percent directly and 21 percent by scattering).
This energy (49 percent) is absorbed by the earth for heating.
Outgoing radiations:
The earth and its atmosphere after absorbing the solar energy in short waves form,
reradiate equivalent amount of heat in the long waves.

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Atmospheric Temperature
Temperature refers to the degree of hotness or coldness of a substance or a thing. The
degree of hotness is known as temperature. Temperature provides a measure of the intensity of
heat energy. Any object receives energy in the form of heat, its temperature increases.
Atmosphere receives the heat energy from the sun and its temperature increases. Differential
heating of two places result into air in motion, thus temperature of air can be regarded as the
basic cause of weather changes.
Importance of air temperature on crop growth
Temperature influences distribution of crop plants and vegetation. The temperature decreases
as altitude increases and this change is responsible for the change of vegetation at different
altitudes.
The growth and development of crop plants are mainly influenced by air temperature. Air
temperature affects leaf production, expansion and flowering. The physical and chemical
processes within the plants are governed by air temperature. The diffusion rate of gases and
liquid is changes with temperature.
Biochemical reactions in crops (double or more than each 100C rise) are influenced by air
temperature.
Solubility of different substances is dependent on temperature.
Temperature affects the stability of enzymatic systems in the plants.
The rate of reactions varies with variations in temperature.
Equilibrium of various systems and compounds is a function of temperature.
Units of temperature measurement
Temperature scale Melting point of water Boiling point of water
Fahrenheit 320 F 2120 F
Celsius 00 C 1000 C
Kelvin 2730 K 3730 K
Atmospheric temperature measurement
Atmospheric temperature is continuously changing (never steady for a long time) therefore its
quantification is important.
Maximum temperature: It is the highest temperature attained by the atmosphere in diurnal
variation.
Minimum temperature: lowest temperature, attained by the atmosphere in diurnal variation.
Average temperature: It represents the average temperature condition of the atmosphere
during 24 hours of the day.
Daily max. + Daily min.
Daily mean temperature =
2

Sum of daily mean of month days

Mean monthly temperature =
Days of the month

Sum of 12 monthly means

Mean annual temperature =
12
Distribution of temperature over earth

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 The temperature distribution over earth is shown with isotherm. Isotherms are the lines on the
weather map connecting places which have same air temperature.
Isotherms run east-west, roughly parallel to each other. Closely spaced isotherms indicate the
rapid temperature changes in horizontal direction and steep temperature gradient. Widely
spaced isotherms are associated with slight temperature changes in horizontal direction and
weak temperature gradient.
Temperature is highest near equator and it decreases gradually towards polar region. The sun
crosses the equator twice in a year therefore two maxima and two minima are observed in
annual cycle near the equator, while one maxima and one minima is observed, outside this zone.
Depending upon the horizontal distribution of temperature earth’s climate is divided in different
zones according to latitude.
00 to 23 ½0 N and S Tropical zone
0 0
23 ½ to 66 ½ N and S Subtropical zone
66 ½0 to 90 N and S Temperate zone
Periodic temperature variations
Annual and diurnal variations of temperature are directly related to the local energy budget.
The annual temperature variations give rise to seasons i.e. summer and winter. In north
hemisphere, minimum temperature will be observed in January (winter) and maximum
temperature will be observed in the month of July (summer) and vice a versa in southern
hemisphere. The main factors contributing to seasonal variations are:-
1. The angel of inclination of solar rays which decides the intensity of radiation.
2. Distance between earth and sun
3. The movement of seasonal winds which contributes to rain and precipitation.
Range: The difference between highest and lowest temperature in a given period. The daily,
monthly, annual ranges are worked out for a station.
The minimum range occurred near equator and maximum in high latitude. The diurnal
temperature variations give rise to daily maximum and minimum temperatures. Maximum air
temperature occurs in between 14 to 16 hrs as per the local mean time, although maximum
amount of solar radiations are received at the solar noon. Delay in occurrence of the maximum
air temperature is caused by the gradual heating of the air by convective heat transfer from the
ground, which is known as thermal lag or thermalinertia. This lag occurs because temperature
continued to rise as long as the amount of incoming solar radiation exceeds the outgoing earth’s
radiation. Although the energy receipt is decline in the afternoon absorption of energy continue
to exceed the energy losses until about 3 pm. Similarly minimum air temperature occurs at
about sunrise. The energy gained during the day is slowly lost to the atmosphere by re-radiation,
resulting in the reduction of temperature. Hence, minimum temperature is reached between 2
to 6 am. Diurnal is the action that is completed within 24 hours and that happen again every 24
hours. This variation is knows as diurnal variation. The temperature distribution varies diurnally
at a given location because of the rotation of the earth. It also varies with latitude, altitude and
the seasons.
Vertical Temperature variations:
Vertical temperature distribution is the base for layering of the atmosphere. As a general rule
throughout the troposphere, the temperature decreases with elevation. Lapse rate of troposphere
i.e. falls in temp with height which is about 6.50C/km. This is also known as static lapse rate
of temperatureor vertical temperature gradient.

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 It is not constant with height in all layers, season and location. Increase in temperature with
height is known as negative lapse rate of temperature or the thermal inversion.
Types of temperature inversion
Surface inversion: Earth surface looses heat more than it gains, resulting a cool air near earth
surface and air above this layer remains warm, and such type of inversion is called as surface
inversion.
Warming by subsidence: When cool air mass from top of hill, tends to flow downward and it
replaces the warm air near the earth surface. This type of surface inversion is call as warming
by subsidence.
From turbulence: Cold air masses replaced by warm air mass when air mass with different
temperature come together due to turbulence and temperature inversion take place which is
called as inversion due to turbulence.
Horizontal temperature variations:
The surface air temperature at particular location depends on the amount of radiation received
by it. Temperature also varies in horizontal direction, due to the horizontal transport (advection)
of heat energy. The rate of change of temperature with horizontal distance is known as
temperature gradient. There is general decrease from equator to poles (increase in latitude).
There may be many locations with same average atmosphere temperatures on a weather map
all such locations are connected by lines of constant temperature know as isotherms.
Factors affecting the atmospheric temperature
Latitude: The rotation and the revolution of earth as well as the inclination of its axis control
duration and intensity of radiation. Due to this different parts of earth’s surface receive different
amount of solar radiation. The amount of total radiations received at the equator and at the
lower latitudes is more intense when compared to that of higher latitudes due to earth’s position
with reference to sun’s rays. But mean annual thermal equator i.e. zone of maximum
temperature is located at about 5oN. This is because the apparent migration of the vertical sun
is relatively rapid during it passage over equator and it is relatively slow when it reaches to
tropics. Between 6oN and 6oS the sun rays remain almost overhead for only 30 days during
spring and autumn equinoxes. On other hand between 17.5o and 23.5o latitude the sun rays shine
down almost vertically for eighty six consecutive days during the period of the solstice i.e.
tropics experience longer period of heating than equator. Heating in north hemisphere is more
as compare to south hemisphere because of presence of continents. Hence over land highest
value occur at about 23oN and 11-15oS.
Altitude: The surface air temperature decreases with increase in altitude from mean sea level
as density of air decreases results in relatively less absorption of earth’s long wave radiation.
As against at surface high density of air, high water vapour content and more dust particles
results in more absorption of earth’s long wave radiation. In troposphere, temperature decrease
with increase in altitude.
Season: The time is one factor which controls temperature. More radiation is received in
summer than in winter because of the higher altitude of the sun and the longer day length.
Distribution of land and water: Water bodies are great moderators of temperature, because
of high specific heat of water. Water is slow in heating and cooling in comparison with land
surface. Difference between maximum temperature and minimum temperature in diurnal
variation is less in the vicinity of water bodies like lake, sea, large water reservoirs. Presence
of smaller ocean area in north hemisphere as compared to south hemisphere results in warmer
summers and cooler winters as against cooler summer and warm winter in north hemisphere.

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Topography (elevation): Mountain ranges affect the temperature by acting as obstacles to the
flow of air near the surface and they often set conditions of warm winds. Temperature also
varies because of slopes direction i.e. north faced slope losses relatively more as compared to
south facing ones. Hence, settlement and cultivation are noticeably concentrated on south
facing slopes i.e. sun facing side whereas north facing side remains forested.
Ocean currents: The energy received over the ocean surface carried away by the ocean
currents from the warm areas to cool areas and there by modifies the temperature in that area.
The warm currents always move from the equator to poles.
Winds: Various types of winds affect the temperature of the any locality. In absence of winds,
we feel warm in hot climate at the same time the weather is pleasant if wind blows.
Clouds and rains: Thick and continuous cloud cover forms a significant barrier to the
penetration of radiation. A drop in surface temperature is often experience when cloud
temporarily cut off direct solar radiation. Over all range of albedo for complete overcast of
cirrostratus is 44 to 50 percent to 90 percent for cumulonimbus. The effect of cloud cover also
operate in reverse, as it serves to retain the heat that otherwise is lost by earth surface in long
wave radiation. Hence, during complete cloudy condition temperatures will be low during day
and warmer during night. Rainfall is having a cooling effect.
Colour of soil: Black colour soil absorb more radiations while other soil types reflect them.
Slope of the land: Perpendicular rays impart more heat while inclined rays less.
Forest and vegetation: Wind, evapotranspiration, interception of sunrays temperatures are
moderated due to present of forest and vegetation.

Effect of Temperature on Plant growth / Crop Productivity

Air temperature is the most important weather parameter which affects the plant life. The
growth of higher plants is restricted to a temperature between 0 to 60oC and the optimum i.e.
10oC to 40 oC. Beyond these limits, plants are damaged severely and even get killed. The
maximum production of dry matter occurs when the temperature ranges from 20 and 30oC. As
already seen the temperature of a place is largely determined by latitude and altitude. Based on
the above the vegetation are classified as tropical (rain forest, desert, grassland), temperate
(Grassland, deciduous forest), taiga (coniferous forest), tundra (low shrubby growth, lichens)
and polar. Some investigators have classified the vegetation of the world into four classes based
on the prevailing temperature conditions. The four classes are 1. Megatherms: Equatorial
and tropical region, tropical rain forests.
2. Merotherms: Tropical and sub-tropical region, tropical deciduous forests.
3. Microtherms: Temperate and high altitude region, alpine vegetation and mixed coniferous
forests.
4. Hekistotherms: Arctic and alpine regions.
High night temperature favours growth of shoots and leaves and it also affects plant
metabolism. On the other hand low night temperature injures the plants. Tender leaves and
flowers are very sensitive to low temperature and frost.
Every plant has its own minimum, optimum and maximum temperature limits for its normal
growth and reproduction with maximum physiological activities and beyond upper and lower
limit of temperature vital physiological activities of a plant will stop. These three levels of
temperature are known as cardinal temperature points.
Minimum temperature: No growth occurs blow this temperature. For typical cool season
crops it ranges between 0 and 50C and for temperate crops between 15 and 180C.

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Optimum temperature: Maximum plant growth occurs in this temperature range. For typical
cool season crop it ranges between 25 and 310C and for temperate crops between 31 and 370C.
Maximum temperature: Growth stops above this temperature. For typical cool season crops
it ranges between 31 and 370C and for temperate crops between 44 and 500C. Cardinal
temperature for the germination of some important crops (Bierhyizen, 1973)
Sr. No. Plant Cardinal temperature 0C
Minimum Optimum Maximum
1 Rice 10-12 30-32 36-38
2 Sorghum 8-10 32-35 40
3 Maize 8-10 32-35 40-44
4 Wheat 3-4.5 25 30-32
5 Barley 3-4.5 20 38-40
6 Sugar beat 4-5 25 28-30
7 Tobacco 13-14 28 35
8 Carrot 4 –5 8 25
9 Pumpkin 12 32-34 40
10 Peas 1-2 30 35
11 Oats 4-5 25 28-3
12 Lentils 4-5 30 36
In General
Cool season crops 0-15 25-31 31-37
Hot season crops 15-18 31-37 44-50
Apart from yield reductions, many visible injuries on the plants are seen due to very low or
very high temperature.
Cold Injury: (Low Air Temperature and Plant Injury)
Chilling injury: Plants which are adapted to hot climate, if exposed to low temperature for
sometime are found to be killed or severely injured. Some effects of chilling are development
of chlorotic condition (Yellowing). E.g. chlorotic bands occur on the leaves of sugarcane,
sorghum and maize in winter months when the night temperature is below 20 0C.
In temperate climate delayed growth and sterility are types of injuries occur because of
low temperature.
Freezing Injury: Plant parts or entire plant may be killed or damaged beyond repair as a result
of actual freezing of tissues. Ice crystals are formed first in the intercellular spaces and then
within the cells. Ice, within the cells, causes more injury by mechanical damage on the structure
of the protoplasm and plasma membrane. Freezing of water in intercellular spaces results in
withdrawal of water from the cell sap due to dehydration and causes death of cells.
Suffocation: In temperate regions, usually during the winter season, the ice or snow forms a
thick cover on the soil surface. As a result the entry of O2 is prevented and plants suffer for
want of O2. Ice coming in contact with the roots prevents the diffusion of CO2 outside the root
zone. This prevents the respiratory activities of roots leading to accumulation of harmful
substances.
Heaving: This is a kind of injury caused by lifting up of the plants along with soil from its
normal position. This type of injury is common in temperate regions. The presence of ice
crystals increases the volume of soil. This causes mechanical lifting of the soil.

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Effect of high Temperatures
Cells of most plant species get killed when the temperature ranges from 50 to 60 0C. This
point of temperature is called Thermal death point. But it varies with the species, age of tissue
and time of exposure to high temperature. It is reported that most plant cells are killed at a
temperature of 45 to 55 0C. Some plants tissues withstand a temperature of up to 105 0C. The
aquatic plants and shade loving plants are killed at comparatively, lower temperature (40 0C);
whereas, for xerophytes it is 50 0C.
High temperature results in desiccation of the plants and disturbs the balance between
photosynthesis and respiration. Higher temperature increases the respiration leading to rapid
depletion of reserve food in plants resulting in growth stunted due to incipient or starvation. As
direct effects on crop plants high temperature causes sterility in flowers. The general effects of
excessive heat are defoliation, pre-mature dropping of fruits. In extreme cases, death of the
plants may also occur.
Heat Injuries:
Sun clad: Injury caused by high temperature on the sides of bark is known as sun clad. This is
nothing but exposure of barks of the stems to high temperature during day time and low
temperature during night time.
Stem girdle: It is another injury associated with high temperature. High temperature at the soil
surface scorches the stems at ground level and further shrinkage of the tissues. The stem girdle
causes the death of the plant by destroying the conductive and cambial tissues or by the
establishment of pathogens in the injury. This type of injury is very common in young seedlings
of cotton in sandy soil where the afternoon soil temperature exceeds 60 0C to 65 0C.
Temperature aberrations
Heat Wave: A region is considered to be in the grip of moderate heat wave when it recorded
maximum temperature exceeds the normal by 50 to 80C. Heat wave is common in UP (54
percent probability) in the month of June. Incidences are more in Western UP particularly more
in June. Persistence is 5-6 days.
Soil Temperature: In many cases soil temperature is more important to plant life than air
temperature. It influences the germination of seeds and root activities. It influences the
soilborne diseases like seedling blight, root rot etc. The decomposition of organic matter will
be more in higher soil temperature with necessary moisture. It controls the nutrient availability.
In tropics high temperature of soil causes regeneration of potato tubers. It also affects
nodulation in legumes.
Cold Waves: A region is said to be in the grip of a moderate cold wave when it recorded
minimum temperature falls short of the normal by 60C to 80C and severe cold wave is prevailed
when the minimum temperature short falls upto 80C generally experienced from November to
March. Severe cold wave generally prevail from January to March common in U. P., Western
U. P. -1 day, Eastern U. P.- 2-7 days.
Storm: A marked atmosphere disturbance characterised by a strong wind, usually accompanied
by rain, snow, sleet (rain that freezes as it falls mixture of rain with snow or hail) or hail and
often thunder and lighting.
Dew Point: The temperature to which air has to be cooled in order to reach saturation.
Dew point is the temperature at which dew starts to form or vapour to condense into liquid.
Degree days: At a given location, the period between planting and harvesting is not a specific
number of calendar days but rather a summation of energy units, which may be represented as
degree days.

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Soil temperature
The surface of the soil is exposed to the direct radiation and air movement. Due to gain of solar
radiation it gets heated and its temperature increases. It gains heat during the day time and
losses some parts during the night to the atmosphere. Soil temperature varies among different
soil types depending upon soil structure, texture and colour at given location through the solar
energy received is the same. It plays important role in seed germination and its initial growth
phase as it is very sensitive to variation in soil temperature. The root zone of any crop is a
function of soil temperature and soil moisture if other environmental factors are homogeneous.
Soil temperature and its influences in crop production:
1. Soil temperature affects entire plant growth, including germination of seed, root
development, etc.
2. Soil temperature affects absorption of water.
3. Soil temperature affects microbial activity. The activity of the nitrobacteria and
heterotrophic organisms increases with rise in soil temp.
4. The field capacity of mineral soil decrease with increase in soil temperature.
5. Rate of decomposition of organic matter and mineralisation of organic forms of nitrogen
increase with increase in soil temperature.
6. Soil temperature affect nutrient uptake, low soil temperature conditions reduces plant
nutrient availability.
7. Soil temperature affects the soil pH. Soil pH increase in winter and decrease in summer.
This is related to microbial activity. pH influences availability of micronutrients such as
manganese, zinc, iron.
8. Soil temperature affects soil air due to change in activity of microbes, which resulted in
CO2 accumulation.
Diurnal changes/Profile of soil temperature:
The diurnal changes in soil temperature depend upon the intensity of solar radiation received
at the surface, the loss of heat by radiation and convection and the rapidity with which heat is
conducted to lower layers. During the day heat moves downward from surface when the surface
soil is hotter and towards the surface at night when the lower soil layers are hotter. Thus there
is an alternate or diurnal rise and fall in soil temperature with the rising and setting of the sun.
It will be noticed that the variation is the greatest in the surface layer upto 20 cm depth. Surface
temperature is doubled in the afternoon compared to morning due to insolation. The lower
layers do not suffer as great a variation as the surface soil that is directly exposed to the sun’s
radiation. The soil temperature remains practically constant or remains unchanged throughout
the 24 hours at depth of about 30 to 90 cm. Variations beyond 30 cm is only due to seasonal
changes or variation.

Seasonal soil temperature changes:

During the cold months of December and January when the air temperatures are low,
the soil temperatures are also low. Therefore, soil temperature begins to rise with the rise in air
temperature. The soil temperature reaches its highest point in May. There is a rapid fall of
temperature with the onset of the monsoon in June. It remains more or less constant at this low
temperature throughout the rainy season. There is a small rise shortly afterwards during

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October, after with the temperature falls again and reaches the lowest point once again in
December.
Method of control of soil temperature:
1.Under field condition, temperature of the soil is controlled by moisture content of soil to a
very large extent. Hence the control of the amount of water in soil helps to regulate its
temperatures. A soil that is over-wet due to water logging or defective drainage has a low
temperature. It remains cold even in the warmest weather. The only way to increase the
temperature of such soils is to remove excess water by providing suitable drains. Improving
the drainage not only restores the air-moisture regime in the soil but also increases its
temperature. The removal of excess water lowers it specific heat and thus increases the
temperature. The increase in the air content of the soil also helps to increase the soil
temperature by lowering the specific heat.
2.On the other hand the vegetation cover, plant shade and the conservation of soil moisture help
to keep the soil temperature low. The shade provided by vegetation reduces the temperature
of the surface soil. This principle is made use of in protecting young seedlings and shallow
rooted crops such as tea, coffee, tobacco, etc. from the intense heat that occurs during summer
or dry spells by providing them with the shade of trees having large canopy.
3.Soil temperature can also be lowered by applying polythene or straw mulch. Mulch keeps the
surface soil cooler, especially during the day, by intercepting insolation and maintaining a
higher level of soil moisture. However at night, it keeps the soil warmer by cutting off the
outgoing radiation.
4.The temperature of surface soil can also be modified by altering its colour, spreading of thin
layer of a white substance like chalk, lowers the temperature by reflecting much of the
incoming radiant energy, while black substance like charcoal powder increases its
temperature as it allows a greater absorption of heat.
6. Use of white polythene increases the soil temperature through greenhouse effect while use
of black polythene increases the soil temperature along with the better weed control.
Effect on crop growth:
In many instances soil temperatures is of greater importance to plant life than air temperature.
For example, peach and oak trees can withstand air temperature of -25 0C but roots of these
trees cannot tolerate even up to 16 0C. It influences the soil borne disease like seedling blight,
root rot, etc. and decomposition of organic matter. Storage and reradiation of insolation causes
changes below surfaces. Conduction of heat to lower layer depends on thermal properties of
the soil. Specific heat, thermal conductivity and thermal diffusivity of the soil influence the
germination of seeds and root activities. More the soil temperature higher will be the
decomposition of organic matter. It controls the nutrient availability. In the tropics high
temperature of soil causes degeneration of potato tubers. It affects nodulation in legumes.

Soil Temperature Regime

Soil temperature is a measure of the amount of heat or radiation from the sun absorbed
by the soil. It is measured in degrees Fahrenheit or Celsius.
Soil temperature is determined by air temperature. Temperature like the soil moisture
state changes with time and usually varies from horizon to horizon in soil. Soil temperature at
the surface can change from hour to hour in a daily cycle. The cycle decreases with soil depth
and is scarcely measurable below a depth of 50cm in most soils.
The temperature at a depth of 10 metres in soil is nearly constant in most soils (e.g.

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tropical soils) and is about the same as the annual mean temperature of the soil above.
Mean annual variation in soil temperature is very slight in the tropical region.
Definition of Soil Temperature Regime: It is the soil property that expresses the change in
temperature of soil over time. In tropical soils, the change is minimal, the difference between
summer and winter soil temperatures being less than 50C.
Possible Soil Temperature Regimes are as below:
Characteristics of regimes for which mean winter and summer soil temperatures vary by more
than 5°C (9°F).
Temperature Regime Mean Annual Temperature in Root Zone (5-100 cm)
(Degrees)
0 0
C F
Pergelic(permanent frost) <0 <32
Cryic(very cold soils) 0–8 32 – 47
Frigid (not cryic or pergelic) 0–8 32 – 47
Mesic 8 – 15 47 – 59
Thermic 15 – 22 59 – 72
Hyperthermic > 22 >72

Characteristics of regimes for which mean winter and summer soil temperatures vary by less
than 5°C (9°F)
Temperature Regime Mean Annual Temperature in Root Zone (5-100 cm)
(Degrees)
0 0
C F
Isofrigid <8 <47
Isomesic 8 – 15 47 – 59
Isothermic 15 – 22 59 – 72
0
Isohyperthermic >22 C >720F

Cardinal Temperature: Temperature required for vital activities of crops.

Cool season crops Hot season crops
Minimum 0-5 0C 15-18 0C
Optimum 25-31 0C 31-37 0C
Maximum 31-37 0C 44-50 0C

Atmospheric pressure

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 The atmosphere is held on the earth by the gravitational pull of the earth. A column of
air exerts weight in terms of pressure on the surface of the earth. The weight of the column of
air at a given place and time is called air pressure or atmospheric pressure. An individual gas
molecule weighs almost nothing; however, the atmosphere as a whole has considerable weight
and exerts an average pressure of1034 grams per square centimetre (14.7 lb/sq. in.) on Earth’s
surface. The reason why people are not crushed by this atmospheric pressure is that air and
water is integral part of blood, tissues, and cells, which exert an equal outward pressure that
balances the inward pressure of the atmosphere. Atmospheric pressure is important because
variation in pressure within the Earth–atmosphere system creates atmospheric circulation and
thus plays a major role in determining our weather and climate. It is the differences in
atmospheric pressure that create winds. Further, the movement of the winds drives our ocean
currents, and thus atmospheric pressure works its way into several of
Earth’s systems.
Atmospheric pressure is measured by an instrument called barometer. Now a days
Fortin’s barometer and Aneroid barometer I are commonly used for measuring air pressure.
Atmospheric pressure is measured as force per unit area. The unit used for measuring pressure
is called millibar. Its abbreviation is ‘mb’. One millibar is equal to the force of one gram per
square centimetre approximately. A pressure of 1000 millibars is equal to the weight of 1.053
kilograms per square centimetre at sea level. It is equal to the weight of a column of mercury
which is 76 centimetre high. The international standard pressure unit is the “pascal”, a force of
one Newton per square meter. In practice atmospheric pressure is expressed in kilopascals, (one
kpa equals 1000 Pa). The mean atmospheric pressure at sea level is 1013.25 millibars. However
the actual pressure at a given place and at a given time fluctuates and it generally ranges
between 950 and 1050 millibars.
Units of atmospheric pressure :
1. Height of mercury column measured in inches, cm, mm.
2. Bar, 1 bar =1000 millibar (mb),
3. SI (standard international) is Pascal.
1 Pascal = Force of 1 Newton per square meter (NM2).
The standard atmospheric pressure is the pressure exerted by atmosphere at mean sea
level at 45 0N (Latitude) and at temperature of 288.150 K i.e. 150C with 1225 g m-2
density of air.
1 Atm = 29.92 inches or 76 cm or 760 mm
= 1013.250 millibar = 1.013 bar
= 1013.25 h Pa i.e. hecto Pascal
= 101.325 Kilo Pascal (KPa),
= 14.7 1 bs inch-2
= 1.013 bar = 10.37 m or ft. of water column.
Conversion of pressure units :
10 m = 1 bar
-2
1 kg cm = 1 bar
14.5 PSI = 1 bar
0.9868 Atm = 1 bar
0.145 PSI = 1 Kpa
101.32 Kpa = 1 Atmosphere

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DISTRIBUTION OF AIR PRESSURE
Distribution of atmospheric pressure on the surface of the earth is not uniform. It varies
both vertically and horizontally.
(a)Vertical Distribution: Air is a mixture of various gases. It is highly compressible. As it
compresses, its density increases. The higher the density of air, the greater is the air pressure
and vice versa. The mass of air above in the column of air compresses the air under it hence its
lower layers are more dense than the upper layers; As a result, the lower layers of the
atmosphere have higher density, hence, exert more pressure. Conversely, the higher layers are
less compressed and, hence, they have low density and low pressure. The columnar distribution
of atmospheric pressure is known as vertical distribution of pressure. Air pressure decreases
with increase in altitude but it does not always decrease at the same rate. Dense components of
atmosphere are found in its lowest parts near the mean sea level. Temperature of the air, amount
of water vapour present in the air and gravitational pull of the earth determine the air pressure
of a given place and at a given time. Since these factors are variable with change in height,
there is a variation in the rate of decrease in air pressure with increase in altitude. The normal
rate of decrease in air pressure is 34 millibars per every 300 metres increase in altitude. The
effects of low pressure are more clearly experienced by the people living in the hilly areas as
compared to those who live in plains. In high mountainous areas rice takes more time to cook
because low pressure reduces the boiling point of water. Breathing problem such as faintness
and nose bleedings are also faced by many trekkers from outside in such areas because of low
pressure conditions in which the air is thin and it has low amount of oxygen content.

Vertical Distribution of Air Pressure

(b) Horizontal Distribution: The distribution of atmospheric pressure over the globe is known
as horizontal distribution of pressure. It is shown on maps with the help of isobars. An isobar
is a line connecting points that have equal values of pressure. Isobars are analogous to the
contour lines on a relief map. The spacing of isobars expresses the rate and direction of change
in air pressure. This charge in air pressure is referred to pressure gradient. Pressure gradient is
the ratio between pressure difference and the actual horizontal distance between two points.
Close spacing of isobars expresses steep pressure gradient while wide spacing indicates gentle
pressure gradient. The horizontal distribution of atmospheric pressure is not uniform in the

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world. It varies from time to time at a given place; it varies from place to place over short
distances. The factors responsible for variation in the horizontal distribution of pressure are as
follows: (i) Air temperature (ii) The earth’s rotation
(iii) Presence of water vapour
(i) Air Temperature: The earth is not heated uniformly because of unequal distribution of
insolation, differential heating and cooling of land and water surfaces. Generally there is an
inverse relationship between air temperature and air pressure. The higher the air temperature,
the lower is the air pressure. The fundamental rule about gases is that when they are heated,
they become less dense and expand in volume and rise. Hence, air pressure is low in equatorial
regions and it is higher in Polar Regions. Along the equator lies a belt of low pressure known
as the “equatorial low or doldrums”. Low air pressure in equatorial regions is due to the fact
that hot air ascends there with gradual decrease in temperature causing thinness of air on the
surface. In polar region, cold air is very dense hence it descends and pressure increases. From
this we might expect, a gradual increase in average temperature towards equator. However,
actual readings taken on the earth’s surface at different places indicate that pressure does not
increase latitudinally in a regular fashion from equator to the poles. Instead, there are regions
of high pressure in subtropics and regions of low pressure in the sub polar areas.
(ii) The Earth’s Rotation: The earth’s rotation generates centrifugal force. This results in
the deflection of air from its original place, causing decrease of pressure. It is believed that the
low pressure belts of the sub Polar Regions and the high pressure belts of the sub-tropical
regions are created as a result of the earth’s rotation. The earth’s rotation also causes
convergence and divergence of moving air. Areas of convergence experience low pressure
while those of divergence have high pressure.
(iii) Pressure of Water Vapour: Air with higher quantity of water vapour has lower
pressure and that with lower quantity of water vapour has higher pressure. In winter the
continents are relatively cool and tend to develop high pressure centres; in summer they stay
warmer than the oceans and tend to be dominated by low pressure, conversely, the oceans are
associated with low pressure in winter and high pressure in summer.
PRESSURE BELT
The horizontal distribution of air pressure across the latitudes is characterised by high
or low pressure belts. This is however, a theoretical model because pressure belts are not always
found as such on the earth. We will see it later how the real condition departs from the idealized
model and examine why these differences occur.
These pressure belts are: (i) The Equatorial Low Pressure Belt (ii) The Sub tropic High Pressure
Belts (iii) The Sub-polar Low Pressure Betts (iv) The Polar High Pressure Belts (i) The
Equatorial Low Pressure Belt: The sun shines almost vertically on the equator throughout the
year. As a result the air gets warm and rises over the equatorial region and produce equatorial
low pressure. This belt extends from equator to 10oNand 10oS latitudes. Due to excessive
heating horizontal movement of air is absent here and only conventional currents are there.
Therefore this belt is called doldrums (the zone of calm) due to virtual absence of surface winds.
These are the regions of convergence because the winds flowing from sub-tropical high
pressure belts converge here. This belt is also known as-Inter Tropical Convergence Zone
(ITCZ).
(ii) The Sub-tropical High Pressure Belts: The sub-tropical high pressure belts extend
from the tropics to about 35o latitudes in both the Hemispheres. In the northern hemisphere it
is called as the North sub-tropical high pressure belt and in the southern hemisphere it is known

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as the South sub-tropical high pressure belt. The existence of these pressure belts is due to the
fact that the uprising air of the equatorial region is deflected towards poles due to the earth’s
rotation. After becoming cold and heavy, it descends in these regions and get piled up. This
results in high pressure. Calm conditions with feeble and variable winds are found here. In
olden days vessels with cargo of horses passing through these belts found difficulty in sailing
under these calm conditions. They used to throw the horses in the sea in order to make the
vessels lighter. Henceforth these belts or latitudes are also called ‘horse latitudes’. These are
the regions of divergence because winds from these areas blow towards equatorial and sub polar
low pressure belts.
(iii) The Sub-polar low Pressure Belts: The sub-polar low pressure belts extend between
45oN and the Arctic Circlein the northern hemisphere and between 45°S and the Antarctic
Circle in the southern hemisphere. They are known as the North sub-polar low and the South
sub-polar low pressure belts respectively. Winds coming from the sub-tropical and the polar
high belts converge here to produce cyclonic storms or low pressure conditions. This zone of
convergence is also known as polar front.

Pressure Belts

(iv) The Polar High Pressure Belts: In Polar Regions, sun never shines vertically. Sun rays
are always slanting here resulting in low temperatures. Because of low temperature, air
compresses and its density increases. Hence, high pressure is found here. In northern
hemisphere the belt is called the North polar high pressure belt while it is known as the South
polar high pressure belt in the southern hemisphere. Winds from these belts blow towards sub-
polar low pressure belts.
In reality, the location of these pressure belts is not permanent. They shift northward in
July and southward in January, following the changing position of the sun’s direct rays as they
migrate between the Tropics of Cancer and Capricorn. The thermal equator (commonly known
as the belt of highest temperature) also shifts northwards and southwards of the equator. With

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the shifting of thermal equator northwards in summer and southwards in winter, there is also a
slight shift in pressure belts towards north and south of their annual average location.
Diurnal and seasonal pressure variation:
A] Diurnal pressure variation:
• At a given station the pressure shows two highs and two lows.
• Two maximums – one at 10 A.M. and another at 10 P.M.
• Two minimums – one at 4.00 P.M. and another at 4.00 A.M.
• Air expansion and air contraction are main reasons for diurnal variation in the air
pressure.
• This variation is more prominent near the equator than at the mid latitudes.
• Equatorial regions absorb more than it loses while the polar region gives up more heat
than they receive.
B] Seasonal pressure variation:
• Due to annual variation in the amount of incoming solar radiation, distinct seasonal
pressure variations are observed.
• Tropical region shows these variations in large as compared to the mid latitude and Polar
Regions.
• Over land high pressure is recorded during the cold season and over the sea during the
warm season.
Classification of pressure systems is based on 1)
High or low pressure systems.
2) Size and duration
3) Origin
I. High or low pressure systems.
High or low pressure systems:
1. High pressure system: In this pressure system high pressure centre is surrounded by
low pressure. Such centres of high pressure are called as high or anticyclone. Direction of
circulation is in North hemisphere clockwise and in South hemisphere anti-clock wise. When
the centre of high pressure elongates, then it is called as ridge. Near 30oN and 30oS the pressure
is called as ridge. Near 30oN and 30oS the pressure is always high because i) intensive hot air
from the equator descends down in this belt and ii) polar air from the subpolar belts also
descents here.
Anticyclones:
Anticyclones play important role in weather phenomena at the surface of the Earth in
comparison with cyclones. The anticyclones are associated with fine weather. They are
secondary atmospheric whirls where in a region of higher atmospheric pressure is located at
the center and spiral air movement is outward from the central area in clockwise motion in the
Northern Hemisphere and counter clockwise in the Southern Hemisphere. The anticyclones are
associated with scantly weather. Subsidence and divergent wind system within an anticyclone
do not favour condensation and cloud formation. In winter, the cold anticyclones originating in
the snow covered sub polar regions always bring with them very low temperature. The middle
latitude anticyclones always produce the lowest temperatures of the season. In summer, the
stagnant type of warm anticyclones associated with the air of tropical of subtropical origin
produce extremely high temperatures called “heat waves”.

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2. Low pressure systems: enter of low pressure is surrounded by high pressure. Centre of
low pressure is called as low or cyclone or depression. Prolonged low pressure centres are
called troughs. The equatorial belt of low pressure is called doldrums (5oN and 5oS of
Equator). It is because
1. Sun falling vertically all-round the year
2. Water vaporisation being high
3. Rising of air
The doldrums belt is spread over Amazon, Congo, Passion and Guniea belt etc.
Cyclones:
The atmospheric disturbances which involve a closed circulation about a low pressure
center, anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere
are called cyclones. It refers to a particular movement of air. There is inward air movement
towards the center. Cyclones cause extensive damage to property and life over land. However,
copious rains received during the cyclonic activity. Cyclones originate and intensify over the
tropical oceans. Cyclones are given different names in different geographical areas Hurricanes
in Atlantic, Typhoons in Western Pacific and South China. The Bay of Bengal is more
vulnerable to cyclones and the East coast is affected frequently when compared to the West
coast as Arabian Sea is relatively less vulnerable due to low sea surface temperature. The super
cyclone that hit Orissa coast during the end of October (27-30 October), 1999 devastated the
low lying areas and the State’s economy was affected very badly due to heavy infrastructure
and losses.
II. Classification based on size and duration: - Pressure system varies in their size and
duration.
1. Large, semi-permanent cells of high and low pressure which can be seen on monthly,
seasonal, yearly pressure charts of the earth. These pressure systems are responsible for
seasonal weather changes.
2. Smaller, short lived moving pressure systems, which are shown on daily weather map.
These are related to daily weather changes.
III. Origins of pressure systems:-
1. Thermal origin: - Column of hot air in the atmosphere is less dense and comparatively
weightless than the column of cold and heavy air of same length. It can be concluded
that most of the low pressure systems are caused by high surface temperature. Some
high-pressure systems are caused by low surface temperature.
2. Non thermal origin: - Some pressure systems are non-thermal origin. These may
results due to mechanical factor affecting air motions i.e. friction by rough land surface
and interruption of mountains to air motion.
Terms related to atmospheric pressure
1. Isobars – These are the lines on the weather map which joins places having equal surface
atmospheric pressure.
2. Pressure gradient – The rate and direction of pressure change per unit horizontal
distance is called the pressure gradient. It is also called as isobaric slope.
3. Isotach – this is the line on the weather map joining the places of equal wind speed.

Atmospheric Humidity
The (invisible) Vapour content of air is known as humidity.

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 Evaporated water enters into the atmosphere. The amount of water in the atmosphere is highly
variable and changes according to season, presence of land or sea, etc. but in any case never
exceeds 4 percent by volume in atmosphere. It exerts pressure on the earth’s surface which is
called as vapour pressure.
Vapour pressure is the force per unit area created by the motion of vapour molecules treated in
isolation apart from all the other gases of atmosphere.
Measures of humidity:
The important measures of humidity are vapour pressure, relative humidity and dew point
temperature. The air contains about 78 percent of Nitrogen, 20 percent of Oxygen and many
other gases including water vapour in small proportions. The pressure of air is the total weight
of all the gases on unit area and water vapour also contributes to this air pressure.
The partial pressure due to water vapour alone is called ‘vapour pressure’. It is expressed in
energy units viz., milli bar or millimeters of mercury, KPa (Kilo Pascal).
When air comes in contact with water it evaporates into air as water vapour. As more and more
water is evaporated amount of water vapour in air increases. However, at any particular
temperature there is a maximum capacity for water vapour that air can hold. At this stage the
air is said to be saturated. The pressure exerted by water vapour under such a standard
conditions is called saturation vapour pressure. The pressure exerted by water vapour
actually present in air is called the actual vapour pressure of air or simply vapour pressure of
air.
The ratio of actual vapour pressure to saturation vapour pressure under fixed conditions of
temperature expressed in percentages in known as relative humidity and is used universally as
a measure of humidity.
Another measure of humidity is the dew point temperature, which is the temperature at which
air get saturated if cooled at constant pressure without addition or removal of water vapour.
Thus, the actual vapour pressure is equal to the saturated vapour pressure at the dew point
temperature. The closer the dew point to air temperature, the nearer is the air to the saturated.
1. Relative humidity (RH):
Actual quantity of water vapour present in a given volume of air
RH % = X 100
Maximum amount of water vapour air can hold in the same volume of air
Relative humidity is expressed in percentage and represents the amount of water vapour
actually present in the air compared with the maximum that could be contained under condition
of saturation at given temperature and pressure. Relative humidity of saturated air is 100
percent.
2. Dew point temperature:
It is the temperature at which the actual mass of water vapour present in a certain volume of
air is just able to saturate it and water vapours begins to condense into water droplets.
3. Absolute humidity (A.H.):
Absolute humidity is defined as the actual mass of water vapour present in the given volume
of air

Wt. of water vapour

A.H. (g/cubic meter) =
Volume of air
4. Specific humidity (S.H.):

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 It is defined as the mass of water vapour in the given mass of air containing moisture

Wt. of water vapours

Specific humidity (gm/kg of air) =
Wt. of moist air
5. Mixing ratio:
Is the mass of water vapour measured in grams mixing with one gram of dry air.

Mass of water vapour Mv Where Mv = Mass of water vapour

= =
Mass of dry air Ma Ma = Mass of dry air

Mv
Specific humidity =
Mv + Ma Diurnal
variations in humidity:
Relative humidity measured twice 7.30 and 14.30. Highest value of R.H. is observed at sunrise
and lowest value at 14 to 16 hrs. Relative humidity of atmosphere is inversely proportional to
atmospheric temperature.
Annual variation:
In summer the RH is low while in monsoon it is high and moderate in winter.
Effect of relative humidity on Plant Growth
Increase in relative humidity decreases the temperature. This phenomenon increases heat load
of the leaves. Since transpiration is reduced no much heat energy is used. Due to closure of
stomata entry of Co2 is reduced. Reduction in transpiration reduces the rate of food
translocation and uptake of nutrients.
Very high RH is beneficial to - Maize, Sorghum, Sugarcane (C4 Plants)
Harmful to - Sunflower, Tobacco.
Affect water requirement of crops:
For almost all the crops it is always safe to have a moderate relative humidity of above 40
percent and 60-80 percent conducive for growth and development of plants.

Evapotranspiration
Evapotranspiration is a bio physical process and this happens in crop's life cycle from
germination to harvest. The components evaporation and transpiration of the term
evapotranspiration are most important segments of hydrologic cycle. Hence, let us understand
the hydrologic cycle of nature first, so as to know the importance of evapotranspiration.
Hydrologic Cycle
It is a never ending process. This is a continuous cycle. The main source of moisture to
the atmosphere is through the process of evaporation. Around 99 per cent of the moisture to the
atmosphere is derived from oceans and only one per cent of moisture is contributed from other
water bodies like river, lakes, wells etc., and also from moist soil and plant surfaces. The water
thus evaporated, form clouds which gives rise to precipitation. The precipitation water is mainly
disposed of on the land as stream flow or infiltration into the ground and a part is stored as
underground water. Again from the land and water bodies evaporation and evapotranspiration
occur and this cycle continues forever and this is known as hydrologic cycle.

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 Schematic diagram of the average annual hydrologic cycle of the earth - atmosphere system

Important Technologies and their Definition

Latent heat: The heat released or absorbed per unit mass by a system during change of phase.
In meteorology at 0°C the latent heat of vaporisation, fusion and sublimation of water are about
600, 80 and 680 calories per gram respectively.
Evaporation (E): This is the phenomenon in which volume of liquid or solid water is lost to
atmosphere from a water body. The volume evaporated per unit area in a unit time (mm day -1)
is defined as evaporation rate.
Pan Evaporation (E pan): Rate of water loss by evaporation from an open water surface of a
pan (mm day-1).
Evapotranspiration (ET): The phenomenon of water transfer into the atmosphere both by
evaporation of liquid or solid water from the surface of the earth and transpiration from the
plants in a crop canopy (or) rate of water loss through transpiration from vegetation plus
evaporation from the soil (mm day-1).
Potential evapotranspiration (PET): The maximum water lost through evaporation from wet
soil and transpiration from a short cut grass, covering ground completely, under unlimited water
supply. In other words it is the atmospheric demand of a particular day.
Reference crop evapotranspiration (ET ): Rate of evapotranspiration from an extended
surface of 8 - 15 cm tall green grass cover of uniform height actively growing, completely
shading the ground and not short of water (mm day-1).
Actual crop evapotranspiration (ETa crop): Rate of evapotranspiration equal to or smaller
than predicted ET crop as affected by a level of available soil water, salinity, field size or other
causes (mm day-1).
Consumptive use (CU): The sum of volume of water taken by vegetation for transpiration and
evaporation from soil, plus water used by the plant for metabolic process (mm day-1).
Transpiration ratio: The effectiveness of the plants in the use of water was often given in
terms of its transpiration ratio. This is the amount of water transpired by a crop in its growth to
produce unit weight of dry matter.

Evaporation (E)
Evaporation is the diffusive process during which a liquid changes into a gas. It is the
physical process by which any liquid escapes from the surface into the air in gaseous state, at a

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temperature below its boiling point. The process of evaporation of water in nature is one of the
fundamental components of the hydrologic cycle by which water changes into vapour through
the absorption of heat energy. This is the only form of moisture transfer from land and ocean
into the atmosphere.
Main natural surfaces which take part in hydrologic cycle through this process are the
oceans, lakes, tanks, ponds, reservoirs, orchards, forests, perennial vegetation, bare soil surfaces
and cropped fields. Evaporation also takes place from fresh snow and ice packs by the process
of sublimation, however, this loss is comparatively small and main loss of evaporation occurs
after snow or ice melts.
The process of evaporation involves supply of energy for the latent heat of vapourisation
and transfer process. The source of energy for evaporation may be the solar energy, the wind
blowing over the surface or the underlying surface itself. The energy required for evaporation,
regardless of the surface where evaporation is taking place is 590 calories per gram of water
evaporated at 20 °C. Based on Dalton's law this fundamental principle of evaporation from a
free surface can be stated as follows:
E = (ea - ed) f(u)
Where, E is Evaporation ea = Saturation vapour pressure at the temperatures of evaporating
surface expressed in mm of Hg; ed = Saturation vapour pressure at the dew point temperature
of the atmosphere (mm Hg); f (u) = function of wind velocity.
Factors affecting evaporation
Evaporation is controlled by many factors and the important factors are as follows: (a)
Energy supply - to provide latent heat for conversion of water into vapour
(b) Vapour pressure deficit of air - to facilitate the escape of water vapour into air
(c) Degree of saturation of soil surface
(d) Temperature of air and soil
(e) Humidity
(f) Wind velocity - to remove water vapour from the evaporating surface and to prevent
saturation of overlying air (g) Density of vegetative cover

Transpiration
Transpiration is the process by which water vapour leaves the living plant body and
enters the atmosphere. It involves continuous movement of water from the soil into the roots,
through the stem and out through the leaves to the atmosphere. Transpiration is basically an
evaporation process with resistance offered by the plant cells. However, unlike evaporation
from a water surface, transpiration is modified by plant structure and stomatal behaviour,
operating in conjunction with the physical principles governing evaporation. Factors
affecting transpiration: The rate of transpiration depends on a) The supply of energy to
vapourise water
b) The water vapour pressure or concentration gradient in the atmosphere which constitutes the
driving force
c) The resistance to diffusion in the vapour pathway.
d) Climatic factors affecting transpiration are light intensity, atmospheric vapour pressure,
temperature and wind
e) The soil factors are those governing the water supply to the root zone of crops and the
presence of sub-surface water-table or impervious layers, etc., if any.

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f) Plant factors include the extent and efficiency of root system in moisture absorption, the leaf
area, leaf arrangement and structure and stomatal behaviour, relative distribution of stomata
on the upper and lower surface of the leaves, variation in stomatal aperture and aerodynamic
roughness of the surface.
Sophisticated instruments like Steady State Porometer is used presently to measure
transpiration at field level. Lysimeters can also be used to measure the transpiration, by using
some barrier to cover the soil surface against evaporation losses.
Evapotranspiration (ET)
The combined loss of water from the plants and the surrounding soil surface through
transpiration and evaporation respectively is jointly called as evapotranspiration (ET).
Consumptive use denotes the quantity of water lost through ET by plants during their growth
plus moisture used for metabolic activities of the plants. Consumptive use is generally taken
equivalent to ET since, the water used in actual metabolic process is insignificant (< 1% of ET).

The factors influencing evapotranspiration are:

a) Climate (to a little extent), b) Water quality and quantity used, c) Planting time d) Variety
used, e) Soil fertility, f) Plant spacing, and e) Use of various chemicals as inputs against weeds,
pest and diseases.
Evapotranspiration will vary from location to location, farm to farm, season to season,
day to day variation in plant growth stages and also due to weather variability. Cloud
Clouds are formed when water evaporates from oceans, lakes, and ponds or by
evapotranspiration over Earth's land surface and rises up into colder areas of the atmosphere
due to convective, orographic, or frontal lifting. The water vapor attaches itself to condensation
nuclei which could be anything from dust to microscopic particles of salt and debris. Once the
vapour has been cooled to saturation, the cloud becomes visible. Clouds clearly indicate or
reflect the physical process taking place in the atmosphere therefore they are good indicators
of weather conditions.
Definition:
Cloud is the mass of tiny droplets or ice crystals or both condensed on hygroscopic nuclei and
found suspending in the atmosphere.
Clouds are defined as a visible aggregation of minute water droplets and / or ice particles
in the air, usually above the general ground level.
Cloud and fog are composed of water droplets or ice crystals or both of the size 20 to 60
microns.
Isoneph:
Line on the weather map joining places of equal cloud cover is known as isoneph.

Cloud observations are to be made under the four heading.

1. Form
2. Amount
3. Direction of motion
4. Height of the bases above station level Amount or cloud cover:
This estimated by the observer and reported as the number of eights of the sky covered
by clouds (octa scale). The station is identified by a circle and the cloud cover is indicated by
proportional filling. Here 9 means, the sky cannot be observed due to poor visibility, so that
could cover cannot be determined.

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WMO Cloud classification:
Clouds have been classified according to their heights and appearance by World
Meteorological Organization (WMO) into 10 categories.
The meaning of cloud names
Main cloud components
Alto: high
Cirrus: thin and wispy
Cumulus: puffy, Latin for stack
Nimbus: precipitation-bearing (Latin for "rain
cloud") Stratus: layer (Latin word for "spread out")
Cloud formation:
Air contains moisture and this is extremely important for the formation of clouds.
• Clouds are formed around microscopic particles such as dust, smoke, salt crystals and other
materials that are present in the atmosphere.
• These materials are called "Cloud condensation Nucleus" (CCN)
• Without these any cloud formation will not take place.
• Certain special types known as "ice nucleus" on which cloud droplets freeze or ice crystals
form directly for water vapour.
• Generally condensation nuclei are present in plenty in air.
• But there is scarcity for special ice forming nuclei.
• Generally clouds are made up of billions of these tiny water droplets or ice crystals or
combination of both.
Clouds and radiation balance:
Clouds may play a dual role in cooling and warming of the earth. If the sky is totally covered
with clouds, clouds act as an active surface instead of the earth surface. The incoming solar
radiation is reflected back to a large extent from the top of clouds and thus low solar radiation
reaches to the earth surface. This may lead to keep the planet cool. On the other hand, they
absorb long wave radiation and emit back in all directions and transmit little long wave
radiation to space. In the process, atmosphere traps huge amounts of heat emitted from the
earth’s surface and clouds, leading to develop the greenhouse effect. In cloudy nights, the effect
of cloud is more and keeps atmosphere warmer. Hence, the normal radiation balance between
the earth, atmosphere and the space is disturbed due to clouds significantly.

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 Cloud family & Name, abbreviation and Possible weather change Description and appearance
height meaning
Family A 1. Cirrus (Ci) thin May indicate storm. Detached clouds in the form of white, delicate filaments or white
High clouds and wispy Showering weather close by or mostly white patches or narrow bands. These clouds have a
7 to 12 km fibrous (hair like) appearance or a delicate silky appearance or
both. All the cirrus or cirro-type clouds are composed of ice
crystals. Cirrus clouds have brilliants colurs of sunset and
sunrise. These clouds do not give precipitation
2. Cirrocumulus (Cc) cirrus Possible storm Thin, white flakes, sheet or layer of cloud without shading.
and cumulus: thin and Composed of very small elements in the form of grains, ripples
wispy and puffy etc. This type of cloud is not common and is often connected
with cirrus or cirrostratus. When arranged uniformly, it forms a
"Mackerel sky". Mackerel fish has Greenish blue stripped back
and silvery white belly. Often fore runners of cyclones.
3. Cirrostratus (Cs) cirrus Storm may be approaching Transparent, whitish cloud veil of fibrous (hair like) or smooth
and stratus : thin and appearance, totally or partly covering the sky and generally;
wispy and spread out producing halo phenomena. This type of cloud is so thin that it
gives the sky a milky appearance, sign of approaching storm or
cyclone.
Family B 4. Altostratus (As) altus Widespread rain or snow Uniform sheet of cloud of gray or bluish colour, frequently
Middle Clouds and stratus: high showing fibrous structure, Produce corona.
3 to 7 km layer
5. Altocumulus (Ac) altus Steady rain or snow White or grey, or both white and grey, patch, sheet or layer of
and cumulus: high heap cloud. They have diverted shedding on their under-surfaces.
Sometimes referred to as "Sheep clouds" or "Woolpack clouds".
It has larger globules than cirrocumulus.

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Cloud family & height Name & abbreviation Possible weather change Description and appearance

Family C 6. Stratocumulus (Sc) Rain possible Large globular masses or rolls of soft gray or white clouds
Low Clouds Ground to stratus and cumulus: with brighter interstices.
3 km layer and heap
7. Stratus (St): May produce drizzles Resembling fog but not resting on ground, Chief winter
layer cloud. Sun is visible through this cloud.
8. Nimbostratus (Nb-St) Continuous rain or snow A dense and shapeless grey or dark low cloud and often
nimbus and stratus: ragged layer. It is thick enough throughout to blot out the
rainbearing layer sun. May give continuous precipitation. It is never
accompanied by lightening, thunder or hail. Streaks of water
(rain) or snow falling from these clouds but not reaching the
ground are called "Virga".
Family D 9. Cumulus (Cu): Fair weather, light Thick, dense cloud with vertical development. The upper
Clouds with puffy precipitation surface is dome shaped with cauliflower structure with
vertical horizontal base line. Cumulus is generally found in the day
development 0.5 to time over land areas.
16 km

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 10. Cumulonimbus (Cb) Sharp showers, thunder storms, Heavy and dense masses of cloud with great vertical
cumulus and nimbus: lightening, hail or tornadoes, development whose summit rise like mountains, towers,
rain-bearing heap etc. anvils. This type of cloud is easily recognised by the fall of
a real shower and sudden darkening of the sky.

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Drought:
Drought is a period of inadequate or no rainfall, over extended time, creating soil moisture
deficit and hydrological imbalance.
Classification of drought:
Drought on different basis is generally classified into three different categories.
(A) On the basis of source of water availability:
Drought is classified into four types on the basis of source of water availability.
1. Meteorological drought:
India meteorological Department (IMD) has defined meteorological drought as the situation
when actual rainfall is less than 75% of the normal rainfall over an area.
2. Hydrological drought:
Definitions of hydrological drought are concerned with the effects of dry spells on surface and
sub-surface hydrology, rather than with the meteorological explanation of the event. Linsley et
al. (1975) considered hydrological drought a ‘period during which stream flows are inadequate
to supply established uses under given water management system’. The frequency and severity
of hydrologic drought is often defined on the basis of water depletion or shortage in reservoirs,
lakes, wells etc. This drought affects industry and power generation. 3. Agricultural drought:
Heatcote (1974) defined agricultural drought as a ‘shortage of water harmful to man’s
agricultural activities. This is the situation resulted from inadequate rainfall when soil moisture
falls short to meet the water demands of the crop during the growing period. This affects crop
growth or crop may wilt due to moisture tress resulting in yield reduction.
4. Socio-economic drought:
The socio-economic effects of drought can also incorporate features of meteorological,
hydrological and agricultural droughts. They are usually associated with the supply and
demand of some economic goods. This drought should be linked not only to precipitation
(supply) but also to trends or fluctuations in demand.
(B) Classification of drought on the basis of time of occurrence:
Drought differs in time and period of their occurrence. On this basis, Thornthwaite
delineated the following three drought areas.
1. Permanent drought area: This is the area of permanent dry, arid or desert regions.
Crop production due to inadequate rainfall, is not possible without irrigation, Vegetation like
cactus, thorny shrubs, xerophytes etc. are generally observed in these areas.
2. Seasonal drought: In the regions with clearly defined rainy (wet) and dry climates,
seasonal drought may result due to large-scale seasonal circulation. This happens in monsoon
areas.
3. Contingent drought: This results due to irregular and variability in rainfall, especially
in humid and sub-humid regions. The occurrence of drought may coincide with critical crop
growth stages resulting in severe yield reduction.
(C) Classification of drought on the basis of medium:
On the basis of medium in which drought occurs, Maximove (1929) has divided drought into
two types.
1. Soil drought: It is the condition when soil moisture depletes and falls short to meet
potential evapotranspiration of crops.
2. Atmospheric drought: This results from low humidity, dry and hot winds and causes
desiccation of plants. This may occur even when the rainfall and moisture supply is adequate.
Meteorological drought based on rainfall deviation:

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 The meteorological drought mainly indicates deficient rain of different quantum, which may
cause hydrological and agricultural, soil and atmospheric drought reducing agricultural and
industrial production. The India Meteorological Department has classified the drought as
fallows on the basis of the rainfall departure.
1. Slight drought: When rainfall deviation is 11 to 26 percent from the normal rainfall.
2. Moderate drought: When rainfall deviation is 26 to 50 percent from the normal
rainfall.
3. Severe drought: When rainfall deviation is more than 50 percent than the normal
rainfall. Drought prone area: A drought prone area is defined as one in which the probability
of a drought year is greater than 20 percent.
Chronic Drought Prone area: A chronic drought prone area is defined as one in which the
probability of a drought year is greater than 40 percent.
Strategies to mitigate the drought:
A. Farm level
The agricultural drought is generally managed by adopting following measures.
1. Preventing and recycling of excess runoff.
2. Deep tillage to absorb and hold maximum moisture.
3. Timely weed management to control water loss by evapotranspiration.
4. Planning for suitable cropping system.
5. Selection of short duration and drought tolerant crops, with low water requirement e.g.
castor, sunflower, sorghum, pearl millet.
6. Adjusting sowing time so as to escape the growth, reproductive stage from the high
probability period of drought.
7. Management of various inputs to overcome the drought situation.
8. Conserving the soil moisture by agronomic practices like mulching, use of
antitransperents to reduce evapotranspiration.
9. Provision of supplemental irrigation from recycled water ever possible.
10. Reduction in plant population thinning of foliage to reduce ET.
B. Government level
It is recognised that country has to be prepared to face the change of an aberrant monsoon in
feature. At present, approximately 28% of the cultivable land is irrigated; the upper limit is
50% of the country. Therefore, the problems of drought prone area have to be tackled on a
long-term basis to minimize adverse effects of drought. Such programme may include the
following points.
1. An early forecast of monsoon to enable farmers to be prepared for a good, normal or
bad season.
2. Improved communication systems.
3. Availability of resources such as credit, fertilisers, pesticides and power for increasing
production.
4. Proper assistance to farmers in the years when monsoon fails.
5. Adequate prices for produce in good year.
6. Building reasonable buffer stocks for food grains.
7. An improved transportation system
8. Crop insurance

Effect of drought

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 1. Depletion soil moisture.
2. Lowering of ground water table.
3. Reduction in agriculture production.
4. Reduction in industrial production.
5. Reduction in power generation.
6. Adverse effect on established economy

Rainfall
Types of rainfall:
Depending on the primary mode of uplift of the air mass, rainfall (precipitation) has three
types as under
1. Convectional rains:
Due to heating of air near ground by surface it becomes hot and light, move upwards which is
known as convection. As it moves upwards it cools at DALR (9.80 C per km) and becomes
saturated hence relative humidity increases to 100 percent and dew point is reached and
condensation begins. Above condensation level further cooling occurs at SALR (40C per km).
Clouds are formed and further after convection results into precipitation. These rains are known
as convectional rains. Convectional rains are common in tropics.
2. Orographic or relief rains:
When the moist air coming from the sea or ocean encounters mountain or relief barrier, it
cannot move horizontally and has to overcome mountain. Air rises upward, cool down and
clouds are formed gives precipitation. Rains possible to windward side only. Air descends after
crossing mountain, further air warmed up, at DALR due to decrease in relative humidity. Less
rain is received to leeward direction. The area is called as rain shadow area.
Leeward side – Pune, Nagar, Nasik receiving less rain
Windward side – Mumbai, Mahabaleshwar and Konkan receives heavy rains. This
results due to Sahyadri ranges.
3. Cyclonic, frontal rains (Disturbance precipitation):
Frontal precipitation: It is produced when two opposing air currents with different
temperatures meet, vertical lifting take place. This convection gives rise to condensation and
precipitation. Similarly the rains received from the cyclones are called as cyclonic rains.
Thunder storm: It is atmospheric disturbance accompanied with thunder and lightening and
some time by hails. This is local storm, covering small area, often causing damage. Chief
Characteristics of thunder storm are formation of cumulo-nimbus cloud accompanied by
copious precipitation, drop in temperature, more or less destructive out thrusting squall wind
which proceeds rainfall. Frequency of thunderstorm decreases with increase in latitude. Its
prerequisites are such that atmosphere must be unstable, usually highly unstable and it should
be highly humid. Lightening, hail, high winds, dust storms, heavy rains and flash flooding
and landslides are common hazards during thunderstorm.
Type of thunderstorm
1. Frontal or general thunderstorm: This occurs over vide areas in convection with
passing of a cyclonic disturbance.
2. Local thunderstorm: Strong heating of the ground with consequent heating of the
overlying air produces strong local convection. Due to expansion of the heated air and it is
forced upward results into its cooling. The rising column of air is cooled until the dew point is
reached. A cumulus clouds forms at this point and continues to develop as long as air continues

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to ascent. With continued ascent, raindrops are formed and start falling. Some reach on ground,
others evaporate. Evaporation causes marked cooling of the surrounding air which then
descends which creates local thunderstorm.
Lightning and thunder
Lightening is the electrical process which includes the high potential electrical
discharge or flash, with creation of tremendous sound and light. It is generally associated with
thunderstorms. Large heat energy is produced.
In the formation of thunderstorm the cumulo-nimbus clouds are produced by upward
motion of the humid air. Many of the raindrops in the cloud are formed by the condensation
and by amalgamation of small drops. In the strong upward motion of the air, these raindrops
are broken up and are electrified positively. The air with its negative charge passes on the
other parts of the clouds. The large quantities of positive and negative charges accumulate in
different regions and the electric forces increase until a lighting flash occur. This process is
repeated. The temperature created is 50,000 0F and at this temperature air gets suddenly
expanded and the molecules and atoms get dissociated with large noise that is thunder.
Hail storm:
It is a most destructive from of precipitation. Size varies from fraction of inch to 2 to
3 inch or big as onion size. It is product of great turbulence within a vertically deep
cumulonimbus cloud.
Dissociation of molecules means separate
Thunder means loud noise of cloud
Flash means bright light for short time

The Origin and Mechanism of Indian Monsoons

Monsoon is actually a wind regime operating at a level of 20 km from the earth’s
surface. It is characterised by seasonal reversal of wind direction at regular intervals. Although
the monsoon is a global phenomenon influenced by a variety of factors not yet completely
understood, the real monsoon rains cover mainly the South Asian region, represented by India,
Myanmar, Sri Lanka, Bangladesh, Bhutan and parts of South East Asia. Besides the
monsoons, the Indian climate is influenced substantially by two more factors. The Himalayas
contribute a continental nature to the climate, recognised by land winds, dry air, large diurnal
range and scanty rainfall. The Indian Ocean, on the other hand, contributes a tropical character
to the Indian climate characterised by uniformity of temperature throughout the year, short
diurnal range, damp air, and frequent rainfall. The monsoon system of the Indian subcontinent
differs considerably from that of the rest of Asia. The centres of action, air masses involved,
and the mechanism of precipitation of the Indian monsoon are altogether different from other
monsoon systems.
Classical Theory or Thermal Concept of Indian Monsoons: According to this theory, the
differential heating of land and sea at the time when the sun makes an apparent northward
movement is the main cause of the Indian monsoonal regime.
Two factors are mainly responsible for this very strong development of monsoons:
(i) Vast size of the Indian subcontinent and adjacent seas;
(ii) Very high and extensive mountain systems of the Himalayas in the north, extending in an
east-west direction, thus posing a formidable physical barrier between tropical and polar
air masses.

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 The second factor is of great meteorological significance. The high mountain chains of
the Himalayas which border the subcontinent on three sides work as both a break and motor at
the same time. During the winter season, they prevent the penetration of the cold polar air
masses from Siberia into the subcontinent, while in summer, the Himalayas do not allow the
equatorial maritime air masses to cross the Himalayas and force them to curve round thenorth-
west. The mighty Himalayas produce hydro-dynamic effects that determine the type of
precipitation in India.
According to the thermal concept, during the period following the Spring Equinox
(March 23), the sun starts its apparent northward shift. As a result, the areas lying north of the
equator (tropics and sub-tropics) get a progressive high incidence of solar radiation. The effect
of this phenomenon ‘on the Indian subcontinent is seen in the form of intense heating of the
vast northern plains and the adjoining highlands. As a result, a massive low pressure trough is
formed extending from the Punjab plains in the north-west to the Bengal delta in the east.
This low pressure zone attracts wind regimes from the adjoining areas, from short
distances in the beginning. But as the level of solar incidence reaches its peak during MayJune,
the pressure gradient between this low pressure trough and the adjoining seas is so great that it
attracts winds from as far as the south of the equator. Accompanying this process and helping
this pull of wind regimes is the development of some high pressure centres—in the Indian
Ocean, Arabian Sea and over Australia (it being the winter season in Australia). The wind
patterns which are prevalent south of the equator are actually the south-east trade winds which
blow from the south-east towards the north-west. These winds, attracted by the low pressure
trough over the Indian subcontinent, while moving north of the equator, turn in a clockwise
direction (or towards the right), following Farrel’s law. This shift in direction is brought about
by the earth’s rotation. Now, the originally south-east trade winds become south-west
monsoons blowing towards the north-east.
At this juncture, the Inter- Tropical Convergence Zone (ITCZ) also shifts northwards.
The ITCZ is the hypothetical line where the north-east trade winds from the northern
hemisphere and the south-east trades from the southern hemisphere meet. The south-west
wands now approaching the Indian peninsula have to travel a long distance over the Indian
Ocean.
During their long journey, these winds pick up large amounts of moisture and by the
time they reach India they are oversaturated. Here, they are known as the south-west monsoons
which get divided into the Arabian Sea branch and the Bay of Bengal branch because of the
shape of peninsular India. There moisture-laden winds cause heavy rainfall on the windward
sides.
The Arabian Sea Branch: This branch of the south-west monsoons strikes the highlands of
the Western Ghats at almost right angles. The windward slopes of the Western Ghats receive
heavy orogenic precipitation. Although the western currents of the monsoon penetrate further
into the Indian mainland the intensity of rainfall goes on decreasing on the leeward side.
While the windward slopes of the Western Ghats are the areas receiving the highest
rainfall, the leeward slopes form a well-marked rain-shadow belt which is drought- prone. For
instance, the average annual rainfall at Mumbai and Pune is 188 cm and 50 cm respectively,
despite the fact that they are only 160 km apart.
The most characteristic feature of the distribution of rainfall on the windward slope is
that the amount of rains is heavier higher up the slopes. However, the heavy rains are
concentrated in a narrow strip along the Western Ghats.

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 After crossing the Western Ghats, the rain- bearing air currents descend the eastern
slopes where they get warmed up adiabatically. This results in a pronounced rain-shadow area.
The higher the mountains-, the larger is the rain-shadow effect. Towards the north, where the
Western Ghats are not very high, the difference in the amount of rainfall between the windward
and leeward side is rather negligible.
Kachchh and Western Rajasthan does not receive because of absence of mountain
barrier to tap the advancing winds. As the Aravallis have an almost north-south axis, they fail
to block the passage of these monsoon currents (which rather blow parallel to the Aravallis)
and lift them. The monsoon currents heading towards Rajasthan are rather shallow and are
superimposed by stable anti-cyclonic air. The hot and dry continental air masses from western
Pakistan (Baluchistan) are drawn towards the thermal low developed in this region. These air
masses check the ascent of air and absorb its moisture. These conditions are unfavourable for
precipitation in Kachchh and western Rajasthan where desert conditions prevail.
Some of the currents from the Arabian Sea branch manage to proceed towards
Chhotanagpur plateau through the Narmada and Tapti gaps. These currents ultimately unite
with the Bay of Bengal branch. Although a few air currents from the main Arabian Sea branch
are diverted northward towards Kachchh and the Thar desert, these currents continue upto
Kashmir without causing rain anywhere on their way. In fact, an east-to- west line drawn near
Karachi in Pakistan practically marks the limit of the monsoon rainfall.
Bay of Bengal Branch: This branch is active in the region from Sri Lanka to Sumatra Island
of the Indonesian archipelago. Like the Western Ghats of India in the case of the Arabian Sea
branch, the windward slopes of the West Coast Mountains of Myanmar (Arakan and
Tenasserim mountains) get heavy rainfall when the main monsoon currents of this branch strike
the Myanmarese coast. Akyab on the west coast records 425 cm during the JuneSeptember
period. As in case of the leeward sides of the Western Ghats in India, here too, the rain shadow
effect is pronounced on the leeward side.
A northern current of this branch strikes the Khasi hills in Meghalaya and causes very
heavy rains. Mawsynram (near Cherrapunji), situated on the southern slopes of Khasi hills, has
the distinction of recording the highest annual average precipitation in the old.
This is because of its peculiar geographical location. Mawsynram is flanked on all sides
by the Garo, Khasi and Jaintia hills except for a gap through which the rain-bearing winds enter
and are forced to rise, thus yielding the heaviest rainfall. Shillong, a mere 40 km away on top
of the Khasi hills, receives only about 140 cm of rainfall during June-September.
Another current of the Bay of Bengal branch takes a left turn at the eastern end of the
low pressure trough (roughly the Bengal delta). From here, it blows in a south-east to northwest
direction along the orientation of the Himalayas. This current causes rainfall over the northern
plains.
The monsoon rainfall over the northern plains is assisted by west-moving monsoon or
cyclonic depressions called ‘westerly disturbances’. These are formed in the Bay of Bengal and
move along the southern fringe of the northern plains causing copious rains there which are
vital for the rice crop.
The intensity of rainfall decreases from east to west and from north to south in the
northern plains. The decrease westwards is attributed to the increasing distance from the source
of the moisture. The decrease in rainfall intensity from north to south, on the other hand, is due
to increasing distance from the mountains which are responsible for lifting the moisture-laden
winds and causing orogenic rainfall in the plains, especially in the foothills.

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 The two main branches of the monsoon winds follow different courses but originally,
they set out to fill the intense low pressure void created in the north-west of the subcontinent.
The two branches meet at the Chhotanagpur Plateau. Of the total moisture carried by the two
branches, only 20 per cent falls as precipitation. The Arabian Sea branch is more powerful of
the two because of two reasons 1. The size of the Arabian Sea is bigger and 2. Most of the
Arabian Sea branch falls over India, while most of the Bay of Bengal branch goes to Myanmar,
Malaysia and Thailand.
Retreating or North-East Monsoons: Towards the end of September, the low pressure centre
in the north-west begins to disintegrate and eventually shifts to the equatorial region. The
cyclonic conditions are replaced by anti-cyclonic ones. As a result, winds start blowing away
from the northern region. Similar anti-cyclonic winds blow from the Tibetan highlands and
beyond.
This is also the time when the sun makes an apparent movement south of the equator.
The Intertropical Convergence Zone (ITCZ) also moves equator wards. Now the winds that
dominate the sub continental landscape are the ones which move from the north-east to the
south-west.
These conditions continue from October till mid-December and are known as the
retreating monsoons or the north-east monsoons. By December end, the monsoons have
completely withdrawn from India. The retreat of the monsoons is markedly gradual in contrast
to the ‘sudden burst’ of the south-west monsoons.
The retreating monsoons over the Bay of Bengal pick up moisture on their way which
is dropped over eastern or coastal Orissa, Tamil Nadu and parts of Karnataka during
OctoberNovember. This is the main season of rains over these areas as they almost lie in the
rainshadow area of the south-west monsoons (Fig.13.21).
During October, easterly depressions occur at the head of Bay of Bengal which move
southwards and in November get sucked into Orissa and Tamil Nadu coasts causing heavy rain,
sometimes with destructive cyclonic winds in coastal and interior areas. The depressions
weaken southwards and towards the interiors.
Winter Monsoons: The stable, dry anti-cyclonic winds prevailing over the subcontinent after
the retreat of the south-west monsoons are not capable of causing precipitation because they
are free of moisture. Instead, these winds produce dry and fine weather. However, certain areas
in the north get winter precipitation: from sources far away.
The north-western parts of India—Punjab and Ganga plains—are invaded by shallow
cyclonic disturbances moving from west to east and having their origin in the Mediterranean
Sea. These are called “Westerly Disturbances’ which travel across West Asia and Afghanistan
before they reach India. These disturbances come with cloudiness and rising temperature in the
front and cold wind in the rear.
These disturbances cause up to 5 cm rainfall in Punjab and Kashmir and up to 2.5 cm
over the Uttar Pradesh plains. These showers are very good for the rabi crop, especially wheat
and gram, and are very effective because of less runoff, less evaporation (because of low winter
temperatures) and the fact that moisture from these showers is confined to the root area of the
crops.

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Reasons and causes of climate change
Climate change refers to the extreme change in climate due to the rapid increase in the
emission of greenhouse gases (GHG). Mainly coal, oil and natural gas are considered to be
responsible for the emission of greenhouse gases. When the infinite rays of the sun reach the
surface of the Earth, a small part of them is absorbed by greenhouse gases into the atmosphere

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of the earth. This causes the temperature of the Earth to rise. This much heat is necessary to
make life possible on the Earth, otherwise the whole Earth will be covered with snow. But
when these gases absorb more heat than required, the average temperature of the Earth
increases and the problem of global warming is created.
Climate change, due to global warming, is a very worrisome issue of our times. The
world is paying a heavy price of increase in population and rapid economic growth as this
progress is not benign and sustainable for the environment. The amounts of GHG such as
Carbon dioxide (CO2), methane (CH4), chlorofluorocarbons (CFCs), nitrous oxide (N2O) and
tropospheric ozone (O3) are increasing in the environment, and the natural balance is
deteriorating. Due to the burning of fossil fuels, coal, oil and natural gas, the GHG level is
increasing in the atmosphere.
Carbon dioxide is increasing in the atmosphere due to gaseous emissions and pollution
caused by industries. As man are also destroying trees, the carbon dioxide accumulated in the
trees is also released in the environment. Due to increase in farming, diversity in land use and
many other sources, there is large-scale secretion of gases like methane and nitrous oxide into
atmosphere.
Nature increases its power to withstand the side effects of this tampering and keeps on
reviving. But in order to enjoy the pleasures of life, man makes artificial objects, which do
not rot and re-enter the natural life cycle. These are synthetic substances, solids, liquids, and
gases which pollute the soil, water and air, affect entire vegetation and organisms.
Climate change has both internal and external reasons. Internal reasons include changes
in natural processes within the climatic system (e.g. heat circulation, volcanic eruptions) or
man-made (e.g. increase in greenhouse gases and dust emission).
Natural causes of climate change:
Many natural causes are responsible for climate change such as the shifting of
continents, volcanoes, sea waves and the Earth’s rotation. Earth’s climate takes thousands of
years to cool down or heat by one degree. The continuous heat released by volcanoes, finer ash
and gases increase the temperature of the atmosphere. The changes that occurred in the
Earth’s climate in the Ice Age cycle were due to volcanic activity, changes in forest life, changes
in sun’s radiation, comets, meteorites and natural changes, etc.
Cyclic changes: Many geologists claim that global warming, due to the intensity of natural
calamities and the increase in temperature of the Earth, is the result of cyclical changes
occurring in the world. They say that such cyclical changes have happened in the past, due to
which we have experienced the Ice Age and have come out of it too.
Continental Drift: The continents that we are familiar with today were formed when the
landmass began gradually drifting apart, millions of years back. This drift also had an impact
on the climate because it changed the physical features of the landmass, their position and the
position of water bodies. The separation of the landmasses changed the flow of ocean currents
and winds, which affected the climate. This drift of the continents continues even today; the
Himalayan range is rising by about 1 mm (millimetre) every year because the Indian land mass
is moving towards the Asian land mass, slowly but steadily. This fragmentation of continents
continues to this day as the continents rest on massive slabs of rock called tectonic plates which
are always moving. All these factors cause climate change.
Volcanic Eruption: When a volcano explodes, it emits sulphur dioxide, water vapour, dust
and ash into the atmosphere in large quantities. Although volcanic activity lasts for a few days,
however, large amounts of gas and dust could influence weather composition for many years.

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With a major explosion, millions of tons of sulphur dioxide can reach the upper layer of the
atmosphere (stratosphere). Gas and dust partially cover the rays coming from the sun. Sulphur
dioxide combines with water to form small particles of sulphuric acid i.e. sulphuric acid. These
particles are so small that they can live on high altitude for years. They are efficient reflectors
of sunlight, and screen the ground from some of the energy that it would ordinarily receive
from the sun. Winds in the upper levels of the atmosphere (stratosphere), carry the aerosols
rapidly around the globe in either an easterly or westerly direction. Movement of aerosols north
and south is always much slower. This give some idea of the ways by which cooling can be
brought about for a few years after a major volcanic eruption. These are able to reverse the
sun’s rays and keep the land deprived of energy that it normally receives from the sun, resulting
in natural imbalance.
Mount Pinatoba, in the Philippine islands erupted in April 1991 emitting thousands of
tonnes of gases into the atmosphere. Volcanic eruptions of this magnitude can reduce the
amount of solar radiation reaching the Earth's surface, lowering temperatures in the lower
levels of the atmosphere (called the troposphere), and changing atmospheric circulation
patterns. The extent to which this occurs is an ongoing debate.
Another striking example was in the year 1816, often referred to as "the year without a
summer." Significant weather-related disruptions occurred in New England and in Western
Europe with killing summer frosts in the United States and Canada. These strange phenomena
were attributed to a major eruption of the Tambora volcano in Indonesia, in 1815.
Earth’s Tilt: The earth makes one full orbit around the sun each year. It is tilted at an angle of
23.5° to the perpendicular plane of its orbital path. For one half of the year when it is summer,
the northern hemisphere tilts towards the sun. In the other half when it is winter, the earth is
tilted away from the sun. If there was no tilt we would not have experienced seasons. Changes
in the tilt of the earth can affect the severity of the seasons - more tilt means warmer summers
and colder winters; less tilt means cooler summers and milder winters.
The Earth's orbit is somewhat elliptical, which means that the distance between the
earth and the Sun varies over the course of a year. It is usually think that the earth's axis as
being fixed, after all, it always seems to point toward Polaris (also known as the Pole Star and
the North Star). Actually, it is not quite constant: the axis does move, at the rate of a little more
than a half-degree each century. So Polaris has not always been, and will not always be, the
star pointing to the North. When the pyramids were built, around 2500 BC, the pole was near
the star Thuban (Alpha Draconis). This gradual change in the direction of the earth's axis, called
precession is responsible for changes in the climate.
Ocean currents: The oceans are a major component of the climate system. They cover about
71 per cent of the Earth and absorb about twice as much of the sun's radiation as the atmosphere
or the land surface. Ocean currents move vast amounts of heat across the planet, roughly the
same amount as the atmosphere does. But the oceans are surrounded by land masses, so heat
transport through the water is through channels.
Winds push horizontally against the sea surface and drive ocean current patterns.
Certain parts of the world are influenced by ocean currents more than others. The coast of Peru
and other adjoining regions are directly influenced by the Humboldt current that flows along
the coastline of Peru. The El Niño event in the Pacific Ocean can affect climatic conditions all
over the world.
Another region that is strongly influenced by ocean currents is the North Atlantic. If we
compare places at the same latitude in Europe and North America the effect is immediately

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obvious. Take a closer look at this example - some parts of coastal Norway have an average
temperature of -2°C in January and 14°C in July; while places at the same latitude on the Pacific
coast of Alaska are far colder -15°C in January and only 10°C in July. The warm current along
the Norewgian coast keeps much of the Greenland-Norwegian Sea free of ice even in winter.
The rest of the Arctic Ocean, even though it is much further south, remains frozen.
Ocean currents have been known to change direction or slow down. Much of the heat
that escapes from the oceans is in the form of water vapour, the most abundant greenhouse gas
on Earth. Yet, water vapour also contributes to the formation of clouds, which shade the surface
and have a net cooling effect. Any or all of these phenomena can have an impact on the climate,
as is believed to have happened at the end of the last Ice Age, about 14,000 years ago.
Radiation from Space: According to former ISRO chairman and physicist Prof. U.R. Rao, the
radiation from the space on Earth is directly related to solar activation. If the activity of the sun
increases, cascade radiation from the universe plays a major role in the formation of lower-
level clouds. The lower level clouds reflect the radiation coming from the sun, due to which
the heat coming from the sun on the Earth goes back to the universe. Scientists found that since
1925, the activity of the sun has increased continuously. Due to which the cascade radiation
that is occurring on the Earth has reduced by almost 9 percent. This has decreased the formation
of special kind of low-level clouds that are formed on the Earth to stop the radiation coming
from the sun.
Human causes of climate change
The Industrial Revolution in the 19th century saw the large-scale use of fossil fuels for
industrial activities. These industries created jobs and over the years, people moved from rural
areas to the cities. This trend is continuing even today. More and more land that was covered
with vegetation has been cleared to make way for houses. Natural resources are being used
extensively for construction, industries, transport, and consumption. Consumerism (our
increasing want for material things) has increased by leaps and bounds, creating mountains of
waste. Also, population has increased to an incredible extent.
All this has contributed to a rise in greenhouse gases in the atmosphere. Fossil fuels
such as oil, coal and natural gas supply most of the energy needed to run vehicles, generate
electricity for industries, households, etc. The energy sector is responsible for about ¾ of the
carbon dioxide emissions, 1/5 of the methane emissions and a large quantity of nitrous oxide.
It also produces nitrogen oxides (NOx) and carbon monoxide (CO) which are not greenhouse
gases but do have an influence on the chemical cycles in the atmosphere that produce or destroy
greenhouse gases.
Greenhouse Emissions: According to IPCC, due to the Industrial Revolution over the last
hundred years, the proportion of carbon dioxide and greenhouse gases has increased in the
atmosphere. Increasing number of factories and vehicles, use of fossil fuels, rapidly rising
population of humans are some of the factors that have contributed to the increase in the amount
of these gases. The excessive emission of greenhouse gases such as carbon dioxide, methane
and nitrous oxide lead to warming of the Earth up to dangerous levels, which cause undesirable
changes in the climate. Due to this, the climate across the world has become highly
unpredictable. As the amount of these gases increases, the quantity of sun’s heat which is
absorbed by them also increases. As a result, the temperature of the Earth has been rising
constantly. According to a recent report of the Intergovernmental Panel on Climate Change
(IPCC), anthropogenic greenhouse gases are responsible for the temperature rise in the
environment, with carbon dioxide contributing the most. IPCC is an intergovernmental

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scientific organization that gathers and analyzes all the social, economic information related to
climate change. The IPCC was formed in 1988 during the General Assembly of the United
Nations.
Some countries of America, Japan and Europe are producing around 75 per cent of the
world’s chloro-fluoro carbon and imposing unwanted illnesses on third world countries. Crores
of people suffer from skin cancer; there are more than a billion people who do not breathe in
clean air. Benzene, carbon monoxide, lead, etc. travel from the reproductive system to heart
rate and blood pressure. Zinc is so dangerous that it snatches children’s memory away and
makes them mentally disabled.
Urbanization and industrialization: Due to industrial activities and increase in number of
vehicles, new greenhouse gases are being secreted in the environment such as
chlorofluorocarbons. Changes in the living conditions of human life in urban areas (due to the
luxurious lifestyle comprising refrigerators, air conditioners, cars etc being widely used) are
greatly contributing to the emission of these gases. In big cities, gases from such sources are
so harmful that on one side they are heating up the Earth and on the other, the ozone layer,
which is the roof over the human communities, is breaking up with ultraviolet rays. In fact,
homes in developed countries emit more carbon dioxide than any car or truck. Large quantities
of wood are used in the construction of buildings. This leads to large-scale denudation of a vast
land of forests. According to the World Resources Institute, the urban population is growing at
a rate of 3.5 percent per annum in developing countries, whereas in developed countries the
rate is less than one percent.
According to the United Nations data, the population of cities will increase in the next
20 years, its 95 percent burden will be on developing countries. That is, by 2030, two billion
people in developing countries will live in cities. The United Nations says that if the increasing
burden and pollution is not controlled in cities, the danger of future floods and other natural
disasters will greatly increase in big cities with more than one crore people. Out of the 21 such
major cities in the world, 75 percent are in developing countries.
Rivers are in crisis. The growing pressures of urbanization have started shrinking and
turning them into drains; all the waste of the city, dirty water and the chemical residues from
the factories, have made them so poisonous that they not able to retain their purity. The amount
of toxic elements such as arsenic and cadmium in the river waters has increased so much it has
posed a threat to humans, animals, birds, trees and plants.
There is indiscriminate use of radioactive chemical compounds, uranium, thorium, etc.
in addition to carbon monoxide, carbon oxide, sulphur dioxide, hydrogen sulphide, carbon
sulphide, chloro-fluoro carbon, nitrogen dye beryliumetc, across the world.
Rising Pollution: Due to the growth in cities and the growing population, pollution is also
increasing. China accounts for 16 cities out of 20 most polluted cities in the world. Due to
pollution, about a million people die prematurely in cities every year. Most of them are from
developing countries only.
Coal-based powerhouses: The main source of energy in urban areas is electricity. All our
domestic machines are run by electrically from thermal power plants. These power plants use
large amounts of fossil fuels (e.g. coal) to generate electricity, leading to a large amount of
greenhouse gases and other pollutants in the atmosphere. With the growing use of coal in
countries like India and China, which are developing rapidly, the monsoon system can become
weak and this can reduce the amount of rainfall in the future.

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 Despite the resolutions made in Paris climate talks, coal has become the primary source
of electricity in Asia and its use has reached its peak in China. Coal is a major reason behind
the emission of man-made sulphur dioxide in China and India. It increases the amount of
sulphate aerosols in the environment. These aerosols do not only harm the health of the people
in the area, but also affect local and global climate change.
Revolutionary changes in technology and transport sector: Indiscriminate use of
technology and vehicles is extracting its price in terms of damage to the environment. The heat
multiples with the increasing use of energy; it is estimated that the filament bulbs which are
burning at night, increase the temperature of the entire atmosphere by more than one degree
Celsius.
Cars, buses and trucks are the main means of transporting people in most cities. They
work mainly on petrol or diesel, which are fossil fuels. It is believed that 20 percent of the
world’s carbon dioxide is emitted due to the diesel/petrol engine installed in vehicles. Coal
mining: Coal mining seems to be a double blow to biodiversity. It has its main role in climate
change; due to coal extraction and evacuation, the entire forest area has been hit by destruction.
Consequently, there has been a tremendous crisis in wildlife and forests in central India.
Unprecedented increase in the area of cultivation: The world history of 250 years has
proved that excessive exploitation of natural resources to increase production has become the
cause of man’s grief. Increasing population means the provision of food for more and more
people. Since there is very limited land area for agriculture (in fact, due to ecological
destruction it is getting narrowed), so more than one fertile crop is grown in most countries.
However, such high-yielding breeds of crops require large amounts of fertilizer; more fertilizer
usage means more emission of nitrous oxide, which is done in both the fields, where it is put,
and the production site. Pollution also takes place by mixing fertilizers in water bodies.
Pesticides used in farming are destroying butterflies, insects and other pests. Indiscriminate
use of plastic/polythene: We produce large quantities of waste in the form of plastic which is
present in the environment for years and damages it. The widely-used polyethylene is making
the air toxic, apart from destroying the Earth’s fertile power. Deforestation: Destruction of
large numbers of forests is also a major reason for global warming. The way the mangrove
forests are cleaned from coastal areas, may leads to the occurrence of disaster like tsunami.
Increasing consumerism, the desire to amass endless means of prosperity, urbanization,
industrialization have exploited nature so much that the forests are getting cleared, and the
Earth is becoming arid and denuded. Under such circumstances, merely celebrating ‘Van
Mahotsav;’ World Forestry Day; Earth Day, or World Environment Day, will not serve the
purpose till people will not adopt concept.
Threat posed by slums: As cities are increasing, the facilities available to the people are
decreasing. People run away to cities in search of a better life, but very few realise their dreams.
According to the World Health Organization (WHO), more than 70 percent of the population
in the developing world (around 90 million) lives in slums. By 2020, this number is estimated
to be two billion. In such a situation where health problems are increasing for them, the
environment also faces serious harm. Due to climate change, the people of the poor and
disadvantaged sections have suffered the most damage.

Greenhouse gases
Carbon Dioxide: Carbon dioxide is undoubtedly, the most important greenhouse gas in the
atmosphere. Changes in land use pattern, deforestation, land clearing, agriculture, and other

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activities have all led to a rise in the emission of carbon dioxide. Accounting for about 76
percent of global human-caused emissions, carbon dioxide (CO2) sticks around for quite a
while. Once it’s emitted into the atmosphere, 40 percent still remains after 100 years, 20 percent
after 1,000 years, and 10 percent as long as 10,000 years later.
Methane: Methane is another important greenhouse gas in the atmosphere. About ¼ of all
methane emissions are said to come from domesticated animals such as dairy cows, goats, pigs,
buffaloes, camels, horses, and sheep. These animals produce methane during the cudchewing
process. Methane is also released from rice or paddy fields that are flooded during the sowing
and maturing periods. When soil is covered with water it becomes anaerobic or lacking in
oxygen. Under such conditions, methane-producing bacteria and other organisms decompose
organic matter in the soil to form methane. Nearly 90 per cent of the paddygrowing area in the
world is found in Asia, as rice is the staple food there. China and India, between them, have
80-90 per cent of the world's rice-growing areas. Methane is also emitted from landfills and
other waste dumps. If the waste is put into an incinerator or burnt in the open, carbon dioxide
is emitted. Methane is also emitted during the process of oil drilling, coal mining and also from
leaking gas pipelines (due to accidents and poor maintenance of sites).
Although methane (CH4) persists in the atmosphere for far less time than carbon dioxide
(about a decade), it is much more potent in terms of the greenhouse effect. In fact, pound for
pound, its global warming impact is 25 times greater than that of carbon dioxide over a 100-
year period. Globally it accounts for approximately 16 percent of human-generated greenhouse
gas emissions.
Nitrous Oxide: A large amount of nitrous oxide emission has been attributed to fertilizer
application. This in turn depends on the type of fertilizer that is used, how and when it is used
and the methods of tilling that are followed. Contributions are also made by leguminous plants,
such as beans and pulses that add nitrogen to the soil.
Nitrous oxide (N2O) is a powerful greenhouse gas: It has a GWP 300 times that of
carbon dioxide on a 100-year time scale, and it remains in the atmosphere, on average, a little
more than a century. It accounts for about 6 percent of human-caused greenhouse gas emissions
worldwide.
Fluorinated Gases: Emitted from a variety of manufacturing and industrial processes,
fluorinated gases are man-made. There are four main categories: hydrofluorocarbons (HFCs),
perfluorocarbons (PFCs), sulfur hexafluoride (SF6), and nitrogen trifluoride (NF3).
Although fluorinated gases are emitted in smaller quantities than other greenhouse
gases (they account for just 2 percent of man-made global greenhouse gas emissions), they trap
substantially more heat. Indeed, the GWP for these gases can be in the thousands to tens of
thousands, and they have long atmospheric lifetimes, in some cases lasting tens of thousands
of years.
HFCs are used as a replacement for ozone-depleting chlorofluorocarbons (CFCs) and
hydrochlorofluorocarbons (HCFCs), usually in air conditioners and refrigerators, but some are
being phased out because of their high GWP. Replacing these HFCs and properly disposing of
them is considered to be one of the most important climate actions the world can take.
Water Vapour: The most abundant greenhouse gas overall, water vapour differs from other
greenhouse gases in that changes in its atmospheric concentrations are linked not to human
activities directly, but rather to the warming that results from the other greenhouse gases we
emit. Warmer air holds more water. And since water vapour is a greenhouse gas, more water
absorbs more heat, inducing even greater warming and perpetuating a positive feedback loop.

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(It’s worth noting, however, that the net impact of this feedback loop is still uncertain, as
increased water vapour also increases cloud cover that reflects the sun’s energy away from the
earth.)
Greenhouse gases and their main sources and sinks.
Gas Lifetime Sources Sinks
Carbon dioxide (CO2) About 25 per Plant and soil respiration, Photosynthesis,
cent of emitted ocean exchange, ocean exchange,
CO2 remains wildfires, volcanoes, weathering of
for over 1,000 fossil fuel use, land use silicate rocks
years change
Methane (CH4) 12 years Microbial processes in Chemical reactions
wetlands, reservoirs, in the atmosphere,
termites, ruminant microbial processes
animals, geological in soils
seeps, wildfires, landfills,
rice paddies, livestock,
fossil fuel extraction
and use

Nitrous Oxide (N2O) 120 years Microbial processes Chemical reactions

in soils, fresh waters in the
and oceans, wildfires, atmosphere
fertiliser
manufacture and use
Chlorofluorocarbons 45 – 1,020 Refrigeration, CFCs Chemical
(CFCs) years propellants, solvents reactions in the
Hydrochlorofluorocarbo <1 – 17 years atmosphere
ns (HCFCs)
Hydrofluorocarbons <1 – 242 years
(HFCs)
Perfluorinated <1 – 50,000 Aluminium production, Chemical reactions
compound (PFC) years semiconductor in the
manufacturing atmosphere
Sulphur hexafluoride gas 3,200 years High voltage electrical Chemical reactions
(SF6) insulation, industrial in the
applications atmosphere
Nitrogen trifluoride ~500 years Semiconductor Chemical reactions
(NF3) manufacturing in the atmosphere
*Anthropogenic sources are in bold.
Global warming
Global warming: Due to global warming, the temperature of the Earth is continuously rising.
Global warming means continuous rise in Earth’s average surface or environmental
temperature due to greenhouse effect. The Earth’s atmosphere is composed of gases like
nitrogen, oxygen, etc which is responsible for maintaining average temperature for life on Earth
at 16 degree Celsius. When the sun rays collide with the Earth’s surface, most of the energy is
absorbed by greenhouse gases such as carbon dioxide, methane, nitrous oxide, sulphur dioxide,
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carbon monoxide, while a part of the solar radiation called infrared radiation returns into space
by means of clouds, snowflakes, and other reflective things.
The rise in sea level, changes in weather, melting of glaciers, decrease in forests,
destruction of many types of organisms and vegetative species, increase in various diseases,
etc are seen in all parts of the world. In fact, global warming is a major issue related to the
existence of mankind.
Reasons/causes of global warming:
Greenhouse effect is the natural process of the environment, it is the ability of the
atmosphere to capture the sun’s warmth keeps the Earth warm to sustain life as this energy
remains present on our Earth in the form of heat. If greenhouse effect does not happens, the
average temperature of the Earth will fall below zero centigrade and the whole earth will be
covered with snow.
Unfortunately since the industrial revolution has occurred, the human activities have
increased the presence of greenhouse gases beyond desirable levels. The amount of sun’s
energy returned into space is gradually reducing as the greenhouse gases absorb more of the
solar radiation, capturing more warmth than required and not allowing the heat to return into
space.
Chlorofluorocarbons (CFCs) form another group of greenhouse gases, which are
responsible for depleting the ozone layer – a high level layer of gas in the stratosphere that
helps to keep out harmful ultraviolet rays. The ozone layer prevents the sun’s dangerous rays
from damaging the Earth. But the holes in the ozone layer are adding to the greenhouse effect.
The most important reason for the increase in the temperature of our Earth is the
continuous increase in the pollution, due to which the level of greenhouse gases is increasing,
which is damaging the ozone layer. With the Industrial Revolution over the last hundred years,
the proportion of carbon dioxide and greenhouse gases has increased in the atmosphere.
Increasing number of factories, vehicles, fossil fuels, and the population of humans all
have contributed to the increase in the amount of these gases. The use of chemical fertilizers
and pesticides is also increasing pollution in soil, water and air. Due to the cutting of trees and
use of fossil fuel (coal) to operate power plants, the level of carbon dioxide is increasing. As a
result, the quantity of sun’s heat absorbed by them has also increased, leading to global
warming.

Effects of global warming

Due to more emissions of harmful substances, glaciers are melting, and sea water levels
are rising, posing a threat to coastal areas around the world. Global warming is also leading to
increasing incidence of droughts, water shortages, famine, floods, landslides, hurricanes,
changes in rain patterns and more such extreme climatic conditions. The temperature of Earth
has increased between 0.4 to 0.8 degrees Celsius (1.4°Fahrenheit) in the last hundred years.
According to the scientists of the Intergovernmental Panel on Climate Change (IPCC),
the global sea level grew to 3.1 mm year-1 from 1993 to 2003. In Europe, there was so much
heat in July-August 2003 that it broke the record of the past 500 years. During this time, 27,000
people died in the heat wave in the world and economic loss of 14.7 billion Euros occurred
while the loss of agriculture, forests and energy sectors could not be assessed. In April-June
1998 alone, 3028 people died due to heat loss in India, while in the cool city like Chicago 528
people died due to hot winds in five days in 1995. On July 13, 1995, the temperature in the city
was recorded at 107°F (42°C). Similarly, in December 1999, in Venezuela, it was so raining

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that about 30000 people were killed. As many as 5748 people were killed due to the cloudburst
from 15 to 17 June 2013 in Kedarnath in Uttarakhand.
In the last 50 years the size of the glaciers has decreased by 16 percent in the United
States of America. In 1972 there were 6 glaciers in Venezuela, which has now reduced to two
and it is estimated that if there is an increase in global temperature, then it will end in the next
ten years.
The rise in sea surface, changes in weather, melting of glaciers, decreasing forests,
destruction of many types of organisms and vegetative species, increase of various diseases,
etc are seen in all parts of the world.
Asia, the United States of America and Europe are responsible for 88 percent of the
world’s total carbon dioxide production. Between 1990 and 2012, they produced 42 percent of
carbon dioxide emissions, 9 percent of nitrogen oxide, 15 percent of methane and double the
amount of chlorinated gases.
According to an estimate, 35 percent of plant and organism species will become extinct
by 2050. In the last week of February 2016 due to the race of economic development, pollution
in China’s capital, Beijing increased so much that the announcement of environmental
emergency had to be made. Similarly, in Delhi in November, 2016, the Indian government
closed schools in the capital for three days and banned construction and demolition for five
days following heavy smog and concentrations of harmful PM2.5 pollutants.
Sea is present in more than 70 percent area of the world and has an extraordinary impact
on global weather, but the heat from global warming is rapidly landing in the sea.
A report published in the Science journal said that the temperature of the sea has been
rising since the last 60 years and now it is growing 13 percent faster than the previous estimates.
Earlier it was said in 1992 that the global sea temperature doubled compared to 1960.
According to the author of the report of this study, the rate of sea water heating has
increased rapidly over the last 60 years as 90 percent of the heat emanating from the greenhouse
gases can be absorbed in the sea.
Experts say that it has been proved that the oceans play an unusual role in the climate
system and their heat is affecting the entire system of the Earth. We have seen that 2016 was
recorded as the hottest year of history.
Following are the effects of global warming at a glance:
1. The melting of glaciers.
2. Depletion of ozone layer.
3. Toxic gases in the environment.
4. Unseasonal rains.
5. Fierce storm, cyclone, hurricanes and droughts.
6. Different types of skin ailments, cancer-related diseases, malaria & dengue.
7. Disappearance of many species of birds and animals who are unable to cope with the
changing environment.
8. Increasing incidence of forest fires.
9. Increasing risk of flood as snow melts on the mountains.
10. Expansion in the desert due fierce heat.
11. Decreasing forest cover.

Climatic Requirement for Fruits, Vegetables and Flowers Crops

Climate

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 Climate is the principal factor controlling plant growth. It refers to the average
condition of the atmosphere over a long period, whereas the term weather is used to describe
the current and temporary atmospheric conditions. For successful growing of horticultural
plants, various components of climate like temperature, humidity, wind, light, rainfall, hail and
frost should be carefully studied.
Man cannot control these environmental factors. It is not possible to make any change
in it. But the effect of these factors can be altered. For these we can take certain steps to increase
or decrease its effects i.e. effect of high or low temperature can be altered, additional moisture
can be given, high wind velocity can be reduced by growing wind break around the orchard.
Climate of a region is mainly influenced by the factors viz. a) latitude b) altitude c)
topography d) position related to continents and oceans e) large scale atmospheric circulation
patterns.
Almost all components of the climate influence horticultural crops. All are closely
interrelated. The effect of each is modified by others. All crops have certain natural threshold
limits of the climatic components beyond which they do not grow normally, but breeding and
selection are gradually extending the threshold for many crops.
Following is a brief account on important climatic components which are affecting the
production of horticultural crops.
1. Temperature: Temperature is one of the most important components of climate. It plays
vital role in the production of horticultural crops. The different activities of plant like growth
and development, respiration, photosynthesis, transpiration, uptake of nutrients and water and
reproduction (Such as pollen viability, blossom fertilization fruit set etc.), carbohydrate and
growth regulators balance, rate of maturation and senescence, and quality, yield and shelf life
of the edible products. The above function of the plant should be well when the temperature at
the optimum range. During high temperature plant does not perform proper functions of
growth, where in low temperature physiological activities of the plant are stopped.
According to different temperature range in the tropics, the specific trees are grown in
different location e.g. apple, pear, peach, almond are successfully grown in the regions of low
temperature known as temperate fruits. In warm winter areas, due to insufficient chilling
temperature fruit trees fail to complete their physiological rest period or meeting their chilling
requirement. As a consequence, buds remain dormant, and leave and blossoms do not appear
on the trees in the following spring. For this reason temperate fruit like apple, apricot, pear and
plums are not considered suitable for tropical or subtropical regions. For tropical and
subtropical fruits the minimum temperature must be within the limit of tolerance of the fruit
species. The fruit grown in tropical and sub-tropical climate is known as tropical fruit and sub-
tropical fruits. Mango, chiku, papaya, banana are successfully grown in high temperature
regions also known as tropical fruits.
The plant performs well in optimum temperature range. The activities of the plant are
affected by very high or very low temperature. The temperature range for plant is
Minimum 4.5° to 6.5°C (40° - 43° F)
Optimum 24° to 27°C (75° - 85° F)
Maximum 29.5° to 45.4°C (85° - 114° F)
Effect of low temperature
The low temperature influenced adversely on plant. There are many effects of low temperature
i.e.
• Desiccation: Imbalance between absorption rate and transpiration rate.

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 • Chilling injury: There is a disturbance in metabolic and physiological process.
• Freezing injury: It is termed as under cooling protoplasm coagulation.
2. Humidity (moisture) and frost: The atmospheric humidity plays a vital role in
deciding the amount of moisture needed to produce a fruit crops. In hot, dry weather enormous
amount of water is lost through transpiration. If the atmosphere is humid, even though hot, the
amount is much smaller and thus a site in humid belt needs less irrigation. High humidity
combined with high temperature also promotes rapid growth. Higher yield but increase
incidence of pests and diseases.
The water requirement of plant also depends on humidity but generally requirement of
water is differed as per different plant species. e.g. to produce 1 kg dry matter pine tree require
25 litres of water, apple required 250 litres, Lucern required 500 litres of water.
The plant gets water from soil, but there are many factors affecting it. i.e. (a) amount of
water in the soil (b) availability of water is also depends on texture and structure of soil (c)
water absorbing area of the tree.
The water is lost from the plant through transpiration by leaves. Transpiration depends
on humidity, temperature, wind, light etc. is necessary to maintain the health of plant by
maintaining the balance between uptake and loss of water.
3. Light: Light is an electromagnetic radiation which is a form of kinetic energy. It comes
from the sun to the earth as discrete particles called quanta or photons.

Light is one of the most important affecting plant life. It is an integral part of the
photosynthetic reaction in that it provides the energy for the combination of carbon dioxide
(CO2) and water (H2O) in the green cells having chlorophyll for the formation of carbohydrates
with release of oxygen. The following equation is to explain the oxidation of water in
photosynthesis.

The performance of crop of growth of plants is influenced by three aspects of light (a) quantity
of light (b) intensity of light (c) duration of light.
a) Light intensity: Light intensity refers to the number of photons falling on a given area
or to the total amount of light which plants receive; the intensity of light varies with the day,
season, distance of equator, dust particles and water vapour in atmosphere, slope of the land

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and elevation. Symptoms associated with low light intensity are decrease in rate of
photosynthesis with normal rates of respiration, decrease supplies of carbohydrates for growth
and yield, leaf tips become discoloured, leaves and bud drop, leaves and flowers become light
in colour. Due to high light intensity, the plant wilts and light coloured leaves may become gray
in colour due to reduction in chlorophyll, the rate of photosynthesis is lowered down while
respiration continues. All above reasons cause low yields.
b) Quality of light: Refers to the length of the waves. The visible part of spectrum of
electromagnetic radiation ranges from wavelength 390 to 730 µm (nanometer). It is also called
photosynthetically active radiation.

In general, red and blue light produce a greater dry weight. Green light inhibits plant
growth. Red light promotes seed germination, growth and flower bud formation in long day
short night plant. Photosynthesis is more in the red region. In apple the blue violet region is
more important for the development of red pigments and colour.
c) Duration of light: Refers to the period for which light is available. Duration of light
required is also known as photoperiod.
Photoperiodism: Response of plant to length daily exposure to the light is known as
photoperiodism or relation of the time of flowering formation of tubers, fleshy roots etc. to the
daily exposure length of period of light.
The plants are mainly grouped into three according to duration of light required.
1. Long day plant: Those plants which require 16 hours or more of daily exposure of
light and short night 8-10 hours of dark period for induction of flowering e.g. radish,
cauliflower, cabbage, carrot, spinach.
2. Short day plant: Those plants which require 12 hours or less of daily exposure of light
and long night 10 to 14 hours dark period for induction of flowering. e.g. strawberry, potato,
sweet potato, chrysanthemum, cosmos, poinsettia etc.
3. Day neutral plants: Day neutral plants are those plants in which flowering are induced
irrespective of duration of light. Such plants are also known as photo insensitive plants. e.g.
tomato, chilli, okra, carnation, dianthus, African violet.
4. Intermediate plants: Those plants which require definite period of daily exposure of
light.
e.g. wild kidney bean, Indian grass, broom grass.
4. Rainfall: This is a very important factor for horticultural crops, and if a garden or
orchard is to be established in a new area it is essential that the pattern of rainfall in the region
be studied before any decision is taken concerning the types of crop to be cultivated.

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Welldistributed and consistent rainfall is always desirable for and ideal orchard site. Rain at the
time of flowering is not suitable, because most of tropical fruit crops are sensitive to rain.
5. Wind: The effect of high wind on crops can be appreciable. Complete physical
destruction may result because little can stand against winds of the order of 100 km/hour, even
large trees become uprooted. Some crops have quite low damage even due to high wind speed.
In many regions high winds can destroy the flowers, fruits etc. Wind breaks can help reduce
this problem. The wind break trees, like saru, eucalyptus, Ingadulsis are growing around the
orchard for protection.

Atmospheric Pollution
Atmospheric pollution is the release of a harmful chemical or material into the
atmosphere. Air pollution is one such form that refers to the contamination of the air,
irrespective of indoors or outside. A physical, biological or chemical alteration to the air in the
atmosphere can be termed as pollution. It occurs when any harmful gases, dust, smoke enters
into the atmosphere and makes it difficult for plants, animals, and humans to survive as the air
becomes dirty.
Air pollution is the introduction into the atmosphere of chemicals, particulates, or
biological materials that cause discomfort, disease, or death to humans, damage other living
organisms such as food crops, or damage the natural environment or built environment.
Air pollution can further be classified into two sections- visible air pollution and
invisible air pollution. Another way of looking at air pollution could be any substance that holds
the potential to hinder the atmosphere or the well-being of the living beings surviving in it. The
sustainment of all things living is due to a combination of gases that collectively form the
atmosphere; the imbalance caused by the increase or decrease in the percentage of these gases
can be harmful to survival.
The Ozone layer considered crucial for the existence of the ecosystems on the planet is
depleting due to increased pollution. Global warming, a direct result of the increased imbalance
of gases in the atmosphere has come to be known as the biggest threat and challenge that the
contemporary world has to overcome in a bid for survival.

Types of Pollutants
Primarily air pollutants can be caused by primary sources or secondary sources. The
pollutants that are a direct result of the process can be called primary pollutants. A classic
example of a primary pollutant would be the sulphur-dioxide emitted from factories.
Secondary pollutants are the ones that are caused by the intermingling and reactions of
primary pollutants. Smog created by the interactions of several primary pollutants is known to
be as a secondary pollutant.

Various Causes of Air pollution

1. The burning of fossil fuels: Sulphur-dioxide emitted from the combustion of fossil
fuels like coal, petroleum and other factory combustibles are one the major cause of air
pollution. Pollution emitting from vehicles on which we rely to fulfil our daily basic needs of
transportation including trucks, jeeps, cars, trains, airplanes cause an immense amount of
pollution.
But, their overuse is killing our environment as dangerous gases are polluting the
environment. Carbon Monoxide caused by improper or incomplete combustion and generally

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emitted from vehicles is another major pollutant along with Nitrogen Oxides, which is
produced from both natural and man-made processes.
2. Agricultural activities: Ammonia is a very common by-product from agriculture
related activities and is one of the most hazardous gases in the atmosphere. Use of insecticides,
pesticides, and fertilizers in agricultural activities has grown quite a lot. They emit harmful
chemicals into the air and can also cause water pollution.
3. Exhaust from factories and industries: Manufacturing industries release a large
amount of carbon monoxide, hydrocarbons, organic compounds, and chemicals into the air
thereby depleting the quality of air. Manufacturing industries can be found at every corner of
the earth and there is no area that has not been affected by it. Petroleum refineries also release
hydrocarbons and various other chemicals that pollute the air and also cause land pollution.
4. Mining operations: Mining is a process wherein minerals below the earth are extracted
using large equipment. During the process dust and chemicals are released in the air causing
massive air pollution. This is one of the reasons which is responsible for the deteriorating health
conditions of workers and nearby residents.
5. Indoor air pollution: Household cleaning products, painting supplies emit toxic
chemicals in the air and cause air pollution. Have you ever noticed that once you paint the walls
of your house, it creates some sort of smell which makes it literally impossible for you to
breathe? Suspended particulate matter popular by its acronym SPM, is another cause of
pollution.
Referring to the particles afloat in the air, SPM is usually caused by dust, combustion, etc.
Pollutants emitted into the atmosphere by human activity include:
Carbon dioxide (CO2): Because of its role as a greenhouse gas it has been described as "the
leading pollutant" and "the worst climate pollution". Carbon dioxide is a natural component of
the atmosphere, essential for plant life and given off by the human respiratory system. CO2
currently forms about 410 parts per million (ppm) of earth's atmosphere, compared to about
280 ppm in pre-industrial times, and billions of metric tons ofCO2 are emitted annually by
burning of fossil fuels. CO2 increase in earth's atmosphere has been accelerating.
Sulphur oxides (SOx): particularly sulphur dioxide, a chemical compound with the formula
SO2. SO2 is produced by volcanoes and in various industrial processes. Coal and petroleum
often contain sulphur compounds, and their combustion generates sulphur dioxide. Further
oxidation of SO2, usually in the presence of a catalyst such as NO2, forms H2SO4, and thus acid
rain. This is one of the causes for concern over the environmental impact of the use of these
fuels as power sources.
Nitrogen oxides (NOx): Nitrogen oxides, particularly nitrogen dioxide, are expelled from high
temperature combustion, and are also produced during thunderstorms by electric discharge.
They can be seen as a brown haze dome above or a plume downwind of cities. Nitrogen dioxide
is a chemical compound with the formula NO2. It is one of several nitrogen oxides. One of the
most prominent air pollutants, this reddish-brown toxic gas has a characteristic sharp, biting
odour.
Carbon monoxide (CO): CO is a colourless, odourless, toxic yet non-irritating gas. It is a
product of combustion of fuel such as natural gas, coal or wood. Vehicular exhaust contributes
to the majority of carbon monoxide let into our atmosphere. It creates a smog type formation
in the air that has been linked to many lung diseases and disruptions to the natural environment
and animals.

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Volatile organic compounds (VOC): VOCs are a well-known outdoor air pollutant. They are
categorized as either methane (CH4) or non-methane (NMVOCs). Methane is an extremely
efficient greenhouse gas which contributes to enhance global warming. Other hydrocarbon
VOCs are also significant greenhouse gases because of their role in creating ozone and
prolonging the life of methane in the atmosphere. This effect varies depending on local air
quality. The aromatic NMVOCs benzene, toluene and xylene are suspected carcinogens and
may lead to leukemia with prolonged exposure. 1, 3-butadiene is another dangerous compound
often associated with industrial use.
Particulate matter / particles, alternatively referred to as particulate matter (PM),
atmospheric particulate matter, or fine particles, are tiny particles of solid or liquid suspended
in a gas. In contrast, aerosol refers to combined particles and gas. Some particulates occur
naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation,
and sea spray. Human activities, such as the burning of fossil fuels in vehicles, power plants
and various industrial processes also generate significant amounts of aerosols. Averaged
worldwide, anthropogenic aerosols—those made by human activities—currently account for
approximately 10 percent of our atmosphere. Increased levels of fine particles in the air are
linked to health hazards such as heart disease, altered lung function and lung cancer. Particulates
are related to respiratory infections and can be particularly harmful to those already suffering
from conditions like asthma.
Persistent free radicals connected to airborne fine particles are linked to cardiopulmonary
disease.
Toxic metals, such as lead and mercury, especially their compounds.
Chlorofluorocarbons (CFCs): harmful to the ozone layer; emitted from products are
currently banned from use. These are gases which are released from air conditioners,
refrigerators, aerosol sprays, etc. On release into the air, CFCs rise to the stratosphere. Here
they come in contact with other gases and damage the ozone layer. This allows harmful
ultraviolet rays to reach the earth's surface. This can lead to skin cancer, eye disease and can
even cause damage to plants.
Ammonia: emitted mainly by agricultural waste. Ammonia is a compound with the
formula NH3. It is normally encountered as a gas with a characteristic pungent odour. Ammonia
contributes significantly to the nutritional needs of terrestrial organisms by serving as a
precursor to foodstuffs and fertilizers. Ammonia, either directly or indirectly, is also a building
block for the synthesis of many pharmaceuticals. Although in wide use, ammonia is both caustic
and hazardous. In the atmosphere, ammonia reacts with oxides of nitrogen and sulphur to form
secondary particles.
Odours: such as from garbage, sewage, and industrial processes.
Radioactive pollutants: produced by nuclear explosions, nuclear events, war explosives,
and natural processes such as the radioactive decay of radon.

Secondary pollutants include:

Particulates created from gaseous primary pollutants and compounds in photochemical
smog. Smog is a kind of air pollution. Classic smog results from large amounts of coal burning
in an area caused by a mixture of smoke and sulphur dioxide. Modern smog does not usually
come from coal but from vehicular and industrial emissions that are acted on in the atmosphere
by ultraviolet light from the sun to form secondary pollutants that also combine with the
primary emissions to form photochemical smog.

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 Ground level ozone (O3) formed from NOx and VOCs. Ozone (O3) is a key constituent
of the troposphere. It is also an important constituent of certain regions of the stratosphere
commonly known as the Ozone layer. Photochemical and chemical reactions involving it drive
many of the chemical processes that occur in the atmosphere by day and by night. At
abnormally high concentrations brought about by human activities (largely the combustion of
fossil fuel), it is a pollutant and a constituent of smog.
Peroxyacetyl nitrate (C2H3NO5) – similarly formed from NOx and VOCs.
Minor air pollutants include:
A large number of minor hazardous air pollutants.
A variety of persistent organic pollutants, which can attach to particulates
Persistent organic pollutants (POPs) are organic compounds that are resistant to
environmental degradation through chemical, biological, and photolytic processes. Because of
this, they have been observed to persist in the environment, to be capable of long-range
transport, bio accumulate in human and animal tissue, bio magnify in food chains, and to have
potentially significant impacts on human health and the environment.
Sources
There are various locations, activities or factors which are responsible for releasing pollutants
into the atmosphere. These sources can be classified into two major categories.
Anthropogenic (man-made) sources:
These are mostly related to the burning of multiple types of fuel.
Stationary sources include smoke stacks of fossil fuel power stations (see for example
environmental impact of the coal industry), manufacturing facilities (factories) and waste
incinerators, as well as furnaces and other types of fuel-burning heating devices. In developing
and poor countries, traditional biomass burning is the major source of air pollutants; traditional
biomass includes wood, crop waste and dung.
Mobile sources include motor vehicles, marine vessels, and aircraft.
Controlled burn practices in agriculture and forest management. Controlled or
prescribed burning is a technique sometimes used in forest management, farming, prairie
restoration or greenhouse gas abatement. Fire is a natural part of both forest and grassland
ecology and controlled fire can be a tool for foresters. Controlled burning stimulates the
germination of some desirable forest trees, thus renewing the forest.
Fumes from paint, hair spray, varnish, aerosol sprays and other solvents.
Waste deposition in landfills, which generate methane. Methane is highly flammable
and may form explosive mixtures with air. Methane is also an asphyxiant (unconsciousness or
death by suffocation) and may displace oxygen in an enclosed space. Asphyxia or suffocation
may result if the oxygen concentration is reduced to below 19.5 per cent by displacement.
Military resources, such as nuclear weapons, toxic gases, germ warfare and rocketry.
Fertilized farmland may be a major source of nitrogen oxides.
Natural sources: Dust from natural sources, usually large areas of land with little vegetation
or no vegetation Methane, emitted by the digestion of food by animals, for example cattle.
Radon gas from radioactive decay within the Earth's crust. Radon is a colourless,
odourless, naturally occurring, radioactive noble gas that is formed from the decay of radium.
It is considered to be a health hazard. Radon gas from natural sources can accumulate in
buildings, especially in confined areas such as the basement and it is the second most frequent
cause of lung cancer, after cigarette smoking.

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 Smoke and carbon monoxide from wildfires. During periods of actives wildfires, smoke
from uncontrolled biomass combustion can make up almost 75% of all air pollution by
concentration.
Vegetation, in some regions, emits environmentally significant amounts of Volatile
organic compounds (VOCs) on warmer days. These VOCs react with primary anthropogenic
pollutants specifically, NOx, SO2, and anthropogenic organic carbon compounds to produce a
seasonal haze of secondary pollutants. Black gum, poplar, oak and willow are some examples
of vegetation that can produce abundant VOCs. The VOC production from these species result
in ozone levels up to eight times higher than the low-impact tree species.
Volcanic activity, which produces sulphur, chlorine, and ash particulates.
Disastrous Effects of Air pollution
1. Respiratory and heart problems: The effects of air pollution are alarming. They are
known to create several respiratory and heart conditions along with Cancer, among other threats
to the body. Several million are known to have died due to direct or indirect effects of Air
pollution. Children in areas exposed to air pollutants are said to commonly suffer from
pneumonia and asthma.
2. Global warming: Another direct effect is the immediate alterations that the world is
witnessing due to global warming. With increased temperatures worldwide, increase in sea
levels and melting of ice from colder regions and icebergs, displacement and loss of habitat
have already signalled an impending disaster if actions for preservation and normalization
aren’t undertaken soon.
3. Acid rain: Harmful gases like nitrogen oxides and sulphur oxides are released into the
atmosphere during the burning of fossil fuels. When it rains, the water droplets combine with
these air pollutants, becomes acidic and then falls on the ground in the form of acid rain. Acid
rain can cause great damage to human, animals, and crops.
4. Eutrophication: Eutrophication is a condition where a high amount of nitrogen present
in some pollutants gets developed on sea’s surface and turns itself into algae and adversely
affect fish, plants and animal species. The green coloured algae that are present on lakes and
ponds is due to the presence of this chemical only.
5. Effect on wildlife: Just like humans, animals also face some devastating effects of air
pollution. Toxic chemicals present in the air can force wildlife species to move to a new place
and change their habitat. The toxic pollutants deposit over the surface of the water and can also
affect sea animals.
6. Depletion of the ozone layer: Ozone exists in the Earth’s stratosphere and is
responsible for protecting humans from harmful ultraviolet (UV) rays. Earth’s ozone layer is
depleting due to the presence of chlorofluorocarbons, hydrochlorofluorocarbons in the
atmosphere. As the ozone layer will go thin, it will emit harmful rays back on earth and can
cause skin and eye related problems. UV rays also have the capability to affect crops.
Solutions for Air Pollution
1. Use public mode of transportation: Encourage people to use more and more public
modes of transportation to reduce pollution. Also, try to make use of carpooling. If you and
your colleagues come from the same locality and have same timings you can explore this option
to save energy and money.
2. Conserve energy: Switch off fans and lights when you are going out. A large number
of fossil fuels are burnt to produce electricity. You can save the environment from degradation
by reducing the number of fossil fuels to be burned.

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3. Understand the concept of Reduce, Reuse and Recycle: Do not throw away items
that are of no use to you. In-fact reuse them for some other purpose. For e.g. you can use old
jars to store cereals or pulses.
4. Emphasis on clean energy resources: Clean energy technologies like solar, wind and
geothermal are on high these days. Governments of various countries have been providing
grants to consumers who are interested in installing solar panels for their home. This will go a
long way to curb air pollution.
5. Use energy efficient devices: CFL lights consume less electricity as against their
counterparts. They live longer, consume less electricity, lower electricity bills and also help
you to reduce pollution by consuming less energy.

Basics of weather forecasting, types, importance of weather forecasting. Forecasting

network in India Weather forecasting:
Any advance information about the probable weather in future obtained by evaluating the
present and past meteorological conditions of the atmosphere is called forecast.
Types of forecast based on validity period:
Weather forecasting on the basis of their validity periods or time scale are classified as
follows.
1. Now casting: Denotes very short range forecasting say few hours from 6 to 24 hours.
2. Short range forecast (SRF): Forecasting is valid for 3 days or 72 hours and are issued
twice a day.
3. Medium range forecast (MRF): Forecasting is valid for 3 to 10 days, period.
4. Long range forecast (LRF): Valid for a period more than 10 days say a month or a
season.
Input required for forecast:
According to type of weather forecast input data required also changes. In general following
input data are required.
1. Surface charts:
The charts give synoptic (means coincident in time) situation prevailing with respect to state
of sky, humidity, wind direction, speed, Atmosphere pressure, visibility, present and past
weather.
2. Upper air charts:
The upper air data with respect to air temperature, dew point temperature, wind speed,
directions at different heights e.g. 850, 700, 500, 300, 200, 100 milli bar surfaces.
3. Cloud imageries by satellite
4. Rainfall: For past 24 hours and deviation from normal
5. Pressure and temperature changes: Taking place during past 24 hours and its
deviation from normal.
Purpose of different type of forecast:
The purpose of each type of forecast differs slightly. The following weather situations
are foretold.
A. Short range forecast:
1. Distribution of rainfall: With warning if any, for heavy rainfall
2. Temperature change: Day and night temperature changes with possible hot and cold
waves.

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3. Important weather systems: This may affect country such as tropical depression, storm
and western disturbances.
4. Special hazardous weather: Like thunderstorm, hail storm, and dust storm, squall,
tornado, snow, frost.
Farmer’s weather bulletin is broadcasted twice a day since 1945. This enables the
farmers to take tactical decisions regarding cultural practices and crop protection programmes
viz., spraying, dusting etc.
B. Medium range forecasting:
Under medium range forecasting, deviation of the weather elements such as temperature,
rainfall from normal values are predicted. Agriculture operations like sowing, planting,
spraying, dusting, irrigation scheduling, crop curing, fertiliser applications, transportation of
agriculture and livestock goods, protection from frost, hails etc. can be planed.
C. Long range forecast:
Outlook for the deviations from the normal conditions or values or some important elements
like rainfall, its quantity and distribution are expressed. IMD issues seasonal long range
forecast as follows:
1. Probable monsoon rainfall: For Kharif season (1st June to 30th September) for peninsular
India and North West India. This is issued in the first week of June.
2. In the first week of August forecast gives summary of rainfall received during June, July
and probable rainfall amount for August and September.
3. In the first week of January: Forecast for winter rains i.e. January- March for the North
West India is given.
Role of Agrometeorological forecast to overcome the losses in crop production.
The losses in crop production can be reduced by making the use of weather forecast as
follows.
1. By avoidance:
Spraying, dusting operation can be avoided or postponed to suitable time if unfavourable
weather warning like that of thunderstorm is predicted which will save costly labours and
chemicals.
2. By protection:
If information on damaging type of weather phenomenon is available in advance necessary
crop protection programme can be planned. Frost can be protected by scheduling irrigation,
lighting burners or application of polythene film on crops.
3. By mitigation:
This process is actually involved in fighting some weather events when it is taking place e.g.
in heavy rain situation provide drainage to field to remove excess water.
Weather forecast need in Agriculture
Weather forecast on the following aspect is needed for agriculture 1.
Occurrences of hail storms of squalls (sudden violent storm wind).
2. Floods.
3. Frost intensity.
4. Rainfall, occurrence time, amount, duration, distribution.
5. Temperature intensity, persistence of cold and hot waves.
6. Wind speed, high wind, tornadoes.
7. Sunshine and cloudy hours.

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 8. Rate of evaporation and evapotranspiration Importance of forecast in
agriculture:
Accurate weather forecasting can help the farmers in realising optimal yield, by reducing the
crop losses. Forecasting helps in
1. Planning for necessary inputs during the season.
2. Timely land preparation to take advantage of earliest rain for timely sowing.
3. Selection of crop and cultivars.
4. Proper time and method of fertiliser application for its efficient use.
5. Predicting pest and disease incidence and frost occurrence for timely action.
6. Timing of weed, pest and disease control.
7. Planning for protecting the crop from weather hazards.
8. Adjustment in crop harvest timing to reduce the loss at harvest.
Weather Service to farmers:
A reliable system of short range and medium range weather forecasts is needed for
effective on farm management practices such as cultivation of land, preparation of seed bed,
planting, choice of crops in case of prolonged monsoon breaks, fertiliser management,
harvesting of crops, post-harvest storage and transportation to markets.
The India Meteorological Department started issuing Farmer’s Weather Bulleting
(FWBs) on a regular basis since 1945 and later it was entrusted to Regional Meteorological
Centers (New Delhi, Mubai, Kolkata, Chennai and Nagpur) which contain a forecast of
expected weather for the next 36 hours and an outlook for another two days. In due course,
meteorological centers at State headquarters started to issue FWBs. All India Ratio used to
broadcast FWBs twice in a day in regional language to reach the most remote corner. However,
they are found to fall short of the requirements of farmers in terms of duration of forecast
validity, capacity for small areas and likely impact on agronomic operations. The crop weather
calendars prepared for main crops lost their significance with fast changing varieties, as they
contain limited information. There was a need to frame them in relation to crops on specific
area-wise. Thus come the concept of Agrometeorological Advisory Services (AAS) and it is in
operation since 1977. However, the utility of the same is very much limited. Realising the
defects and make the AAS more meaningful, the National Centre for Medium Range Weather
Forecasting (NCMRWF) took up the task in 1988 based on medium range weather forecasting.
Agromet Advisory Services (AAS)
The agroadvisory service based on medium range weather forecasting (validity 3 to 10
days) has been made operational by India meteorological department (IMD). The ICAR and
State Agricultural Universities co-operate in this task. IMD has proposed to establish 530
DAMU (District agro-met units) in all the KVKs, which will cover the entire country. So far,
130AMFUs (Agro-met field unit) are established in ICAR and State Agricultural Universities
till date. The agro climatic zones were delineated by the ICAR under the National Agricultural
Research Project (NARP). The AMFUs prepare AAS bulletins. These contain three parts. The
first part of AAS consists of weather events occurred during the past week and weather forecast
for three days ahead. These forecasts are given to acquaint the farmer with the expected weather
on cloud amount, rainfall, average wind speed, wind direction, maximum and minimum
temperatures and weekly cumulative rainfall. The second part contains the factual information
on varieties/crops, their state and stage, ongoing agricultural operations and incidence of insect
pest and diseases of crops. The final and third part of the AAS bulletin provides information
on agro advisory. The bulletins are prepared by the Agrometeorological Advisory Board,

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consisting of scientists belong to various disciplines and Agricultural Officers of the locality.
Such AAS bulletins are being prepared and issued in English as well in local languages. The
AMFUs functioning at several agro climatic zones have made the weekly/ biweekly AAS. The
IMD provides information on MRF twice in a week,every Tuesday and Friday to all the
established AMFUs.
Dissemination of Agromet Advisory Services:
The agro advisory bulletins prepared biweekly by the AMFUs could be
communicated on the same day/next to the selected farmers through a special messenger. The
AIR, DD and other communication faculties can be effectively used to disseminate AAS. It is
being done is several parts of the country. It is hoped that by the end of this decade, all the 127
agroclimatic zones will be covered under the scheme.

Remote Sensing The word ‘remote sensing’ was coined by

Fischer in 1960 AD.
Remote sensing is defined as, ‘The collection and interpretation of information about a
target without being in physical contact with it’ or
According to Lilesand and Kiefer Remote sensing is the science and art of obtaining
information about an object, area, phenomenon through the analysis of data acquired by a
device that is not in contact with the object, area or phenomenon under investigation.
Remote sensing is defined as the art and science of gathering information about objects
or areas from a distance without having physical contact with objects/ areas being investigated.
Principles of remote sensing
Every material on the earth absorbs and reflects the solar energy. In addition, also emit certain
amount of internal energy. The absorbed, reflected and emitted energy is detected by remote
sensing instruments or sensors which are carried in aircraft or satellites. The detections are
made by characteristic terms called “Spectral signatures” and “images”. Remote sensing
systems in common use, record radiation in the form of electromagnetic spectrum (sunlight)
i.e. visible range (0.4 – 0.7 nm), near infrared (0.7 - 1000 nm) and microwaves (1 nm - 0.8 nm).
Artificial sources of illumination such as radar's are also used in some way.
Sensors used in remote sensing
The scientific means of obtaining information in remote sensing include various sensors.
Human eyes (Elector Magnetic Visible Spectrum), human ear (audio range), telescope, camera
are some common examples of the remote sensors. In 1960, the launching of surveillance
satellite marks the new era in remote sensing.
i. Photography: Photographic systems are the most commonly used sensing systems. The
film records the energy reaching it at the exposure time in the visible and near infrared
ranges of the spectrum. The photographic technique is used to identify soil types, plants
grown, disease incidence and drainage patterns.
ii. Line scan and related system: Uses the visible and near infrared portion of the spectrum.
In this system a mirror is rotated parallel to the direction of the movement of the aircraft or
satellite. The mirror reflects the radiation received on to a detector and the data are
recorded.
The multi spectral scanners have different channels for different colours of visible band and
infrared portions. The infrared sensors also recorded the thermal infrared radiation emitted
by the earth proportional to the surface temperature. The infrared imagery is used to study
the extent of vegetation, soil moisture, etc.

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iii. Microwave system: The microwave radiations emitted from earth surface is in small
quantity and is used by microwave sensors in a wave length of about 1 nm to 1000 nm. The
sensors record the microwave radiation through a complex antenna. These are used in
weather satellites. The active microwave systems are known as radars. Radars are used to
study soil characters, plant condition, soil moisture and runoff slopes. Areas of general
application: i) Agricultural land used mapping
ii) Agricultural population
distribution iii) Land used potential
and iv) Soil and water resource
surveys.
Areas of specific application:
1. Monitoring agricultural operations during season: All the farm operations like sowing,
inter-cultivation, harvesting etc is being monitored effectively by the remote sensing.
2. Crop identification: By using LISS II or III seasons crop identification on regional scale
is possible.
3. Crop acreage estimation: By using stratified sampling methodology crop acreage
estimation is done to the high level precision.
4. Crop yield estimation: The crop yields are estimated by analyzing satellite based
vegetation indices which are transformation of reflectance in the near infrared portions of
electromagnetic spectrum.
5. Monitoring of crop phonology and stresses: The crop condition is affected by several
factors like deficiency of nutrients, acidic and salinity problems of soil, nutrient
deficiencies, adverse weather conditions etc. all these can be detected by remote sensing.
6. Damage estimation and command area management: The damages due to floods,
cyclones, water logged areas in command area etc. can be detected and managed effectively
by using techniques like the multi-temporal remote sensing.
7. Water availability and soil moisture estimation: The surface and subsurface water
availability for irrigation and the amount of moisture available in the upper few centimeters
of the soil can be found with a greater accuracy.
8. Land degradation and watershed management: The remote sensing technology is
highly useful in identifying and delineating degraded lands. Also facilitates in delineation
of the watershed areas.
9. Drought detection and management: The drought realistically and ways to mange the
adverse effect is possible through remote sensing.
10. Desertification: Remote sensing provides information to identity the important indicators
of desertification. Based on this, action can be taken by the planners at different levels.
Remote sensing in India
In 1920, the first air survey using aerial photography was conducted.
In 1926, Aerial photography was used to asses flood situation.
In seventies, ISRO (Indian Space Research Organisation) used remote sensing for resource
inventory.
Sr. Satellite Launch Date Launch Vehicle Remarks
No.
1. Aryabhata 19Apr1975 Intercosmos Provided technological experience
in building and operating a satellite
system.
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2. Bhaskara-I 07Jun1979 Intercosmos First experimental remote sensing
satellite. Carried TV and microwave
cameras.
3. Rohini 10Aug1979 Satellite Launch Intended for measuring in-flight Technology
Vehicle (SLV) performance of first experimental
Payload flight of SLV-3, the first Indian
launch vehicle. Did not achieve orbit.
4. Rohini RS-1 18Jul1981 SLV-3 Used for measuring in-flight
performance of second experimental
launch of SLV-3.
5. Rohini RS-D1 31May1981 SLV-3 Used for conducting some remote
sensing technology studies using a
landmark sensor payload. Launched
by the first developmental launch of
SLV-3.
6. Ariane 19Jun1981 Ariane First experimental communication Passenger satellite.
Provided experience in
Payload building and operating a payload Experiment experiment three-
axis stabilised
communication satellite.
7. Bhaskara-II 20Nov1981 Intercosmos Second experimental remote
sensing satellite; similar to
Bhaskara-1. Provided experience in
building and operating a remote
sensing satellite system on an endto-
end basis.
8. INSAT-1A 10Apr1982 Delta launch First operational multipurpose vehicle
communication and meteorology
satellite. Procured from USA.
Worked for only six months.
9. Rohini RS-D2 17Apr1983 SLV-3 Identical to RS-D1. Launched by
the second developmental launch of
SLV-3.
10. INSAT-1B 30Aug1983 U.S. Space Shuttle Identical to INSAT-1A. Served for
more than design life of seven years.
11. IRS-1A 17Mar1988 Vostok Earth observation satellite. First
operational remote sensing satellite.
Mission Completed
12. Stretched 24Mar1987 ASLV Carried payload for launch vehicle
Rohini performance monitoring and for
Satellite Series gamma ray astronomy. Did not
(SROSS-1) achieve orbit.
13. Stretched 13Jul1988 ASLV Carried remote sensing payload of

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 Rohini German space agency in addition to Satellite Series Gamma Ray astronomy
payload.
(SROSS-2) Did not achieve orbit.

14. INSAT-1C 21Jul1988 Ariane Same as INSAT-1A. Served for

only one-and-a-half years.
15. INSAT-1D 12Jun1990 Delta launch Identical to INSAT-1A. Still in vehicle
service.
16. IRS-1B 29Aug1991 Vostok Earth observation satellite.
Improved version of IRS-1A.
Mission Completed
17. Stretched 20May1992 ASLV Carried gamma ray astronomy and
Rohini aeronomy payload.
Satellite Series
(SROSS-C)
18. INSAT-2DT 26Feb1992 Ariane Launched as Arabsat 1C. Procured
in orbit from Arabsat in 1998.
19. INSAT-2A 10July1992 Ariane First satellite in the second-
generation Indian-built INSAT-2
series. Has enhanced capability over
INSAT-1 series. Still in service.
20. INSAT-2B 23Jul1993 Ariane Second satellite in INSAT-2 series.
Identical to INSAT-2A. Still in
service.
21. IRS-1E 20Sep1993 PSLV-D1 Earth observation satellite. Did not
achieve orbit.
22. Stretched 04May1994 ASLV Identical to SROSS-C. Still in
Rohini service.
Satellite Series
(SROSS-C2)
23. IRS-P2 15Oct1994 PSLV-D2 Earth observation satellite.
Launched by second developmental
flight of PSLV. Mission Completed
24. INSAT-2C 07Dec1995 Ariane Has additional capabilities such as
mobile satellite service, business
communication and television
outreach beyond Indian boundaries.
Still in service.
25. IRS-1C 28Dec1995 Molniya Earth observation satellite.
Launched from Baikonur
Cosmodrome. Mission Completed
26. IRS-P3 21Mar1996 PSLV-D3 Earth observation satellite. Carries remote
sensing payload and an Xray astronomy payload. Launched

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 by third developmental flight of
PSLV. Mission Completed
27. INSAT-2D 04Jun1997 Ariane Same as INSAT-2C. Inoperable
since 1997-10-04 due to power bus
anomaly.
28. IRS-1D 29Sep1997 PSLV-C1 Earth observation satellite. Same as
IRS-1C. Still in service.
29. INSAT-2E 03Apr1999 Ariane Multipurpose communication and
meteorological satellite.
30. IRS-P4 26May1999 PSLV-C2 Earth observation satellite. Carries
OCEANSAT an Ocean Colour Monitor (OCM)
and a Multi frequency Scanning
Microwave Radiometer (MSMR).
Still in service.
31. INSAT-3B 22Mar2000 Ariane Multipurpose communication:
business communication,
developmental communication, and
mobile communication.
32. GSAT-1 18Apr2001 GSLV-D1 Experimental satellite for the first
developmental flight of Geosynchronous Satellite Launch
Vehicle, GSLV-D1.
33. Technology 2001-10-22 PSLV-C3 Experimental satellite to test
Experiment technologies such as attitude and
Satellite (TES) orbit control system, high-torque
reaction wheels, new reaction control
system, etc. In Service
34. INSAT-3C 24Jan2002 Ariane Designed to augment the existing
INSAT capacity for communication
and broadcasting and provide
continuity of the services of INSAT-
2C.
35. Kalpana-1 12Sep2002 PSLV First meteorological satellite built
by ISRO. Originally named
METSAT. Renamed after Kalpana
Chawla who perished in the Space
Shuttle Columbia.
36. INSAT-3A 10Apr2003 Ariane-5 Multipurpose satellite for
communication, broadcasting, and
meteorological services along with
INSAT-2E and Kalpana-1.
37. GSAT-2 08May2003 GSLV Experimental satellite for the second
developmental test flight of
Geosynchronous Satellite Launch
Vehicle (GSLV)
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38. INSAT-3E 28Sep2003 Ariane-5 Communication satellite to augment the
existing INSAT System.
39. RESOURCES 17Oct2003 PSLV-C5 Earth observation/remote sensing AT-1 (IRS-P6)
satellite. Intended to supplement
and replace IRS-1C and IRS-1D. In
Service
40. EDUSAT 20Oct2004 GSLV Also designated GSAT-3. India’s
first exclusive educational satellite.
41. HAMSAT 05May2005 PSLV Microsatellite (42.5 kilograms) for
providing satellite-based amateur
radio services to the national as well
as the international community.
42. CARTOSAT-1 05May2005 PSLV-C6 Earth observation satellite. Provides
stereographic in-orbit images with a
2.5-meter resolution. In Service
43. INSAT-4A 22Dec2005 Ariane Advanced satellite for direct-to-
home television broadcasting
services.
44. INSAT-4C 10Jul2006 GSLV Geosynchronous communications satellite. Did
not achieve orbit.
45. CARTOSAT-2 10Jan2007 PSLV-C7 Advanced remote sensing satellite
carrying a panchromatic camera
capable of providing scene-specific
spot images. In Service
46. Space Capsule 10Jan2007 PSLV-C7 Experimental satellite intended to
Recovery demonstrate the technology of an
Experiment orbiting platform for performing (SRE-1) experiments in
microgravity
conditions. Launched as a
copassenger with CARTOSAT-2.
SRE-1 was de-orbited and recovered
successfully after 12 days over Bay
of Bengal.
47. INSAT-4B 12Mar2007 Ariane Identical to INSAT-4A. Further
augments the INSAT capacity for
direct-to-home (DTH) television
services and other communications.
48. INSAT-4CR 02Sep2007 GSLV-F04 Identical to INSAT-4C. Provides
direct-to-home (DTH) television
services, video picture transmission
(VPT), and digital satellite news
gathering (DSNG).
49. CARTOSAT- 28Apr2008 PSLV-C9 Earth observation/remote sensing
2A satellite. Identical to CARTOSAT-

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 2. In Service
50. IMS-1 (Third 28Apr2008 PSLV-C9 Low-cost microsatellite imaging World Satellite
mission. Launched as co-passenger
– TWsat) with CARTOSAT-2A.
51. Chandrayaan-1 22Oct2008 PSLV-C11 Unmanned lunar probe. Carries 11
scientific instruments built in India,
USA, UK, Germany, Sweden and
Bulgaria.
52. RISAT-2 20Apr2009 PSLV-C12 Radar imaging satellite used to
monitor India's borders and as part of
anti-infiltration and anti-terrorist
operations. Launched as a
copassenger with ANUSAT.
53 ANUSAT 20 April PSLV-C12 Research microsatellite
designed at 2009 Anna University. Carries an
amateur radio and technology
demonstration experiments.
54. Oceansat-2 23 PSLV-C14 Gathers data for oceanographic, (IRS-P4)
September coastal and atmospheric 2009 applications. Continues mission of
Oceansat-1.
55. GSAT-4 15 April GSLV-D3 Communications satellite
2010 technology demonstrator. Failed to
reach orbit due to GSLV-D3 failure.
56. CARTOSAT- 12 July 2010 PSLV-C15 Earth observation/remote sensing
2B satellite. Identical to CARTOSAT-
2A
57. GSAT-5P Dec 25, 2010 GSLV-F06 Communication, Failed to reach
orbit
58. YOUTHSAT Apr 20, 2011 PSLV-C16 Student satellite
59. RESOURCES Apr 20, 2011 PSLV-C16 Earth Observation AT-2
60. GSAT-8 May 21, Ariane-5 VA-202 Communication, Navigation
2011
61. GSAT-12 Jul 15, 2011 PSLV-C17 Communication
62. Megha- Oct 12, 2011 PSLV-C18 Climate & Environment, Earth
Tropiques Observation
63. RISAT-1 Apr 26, 2012 PSLV-C19 Communication
64. GSAT-10 Sep 29, 2012 Ariane-5 VA-209 Communication, Navigation
65. GSAT-10 Sep 29, 2012 Ariane-5 VA-209 Communication, Navigation
66 IRNSS-1A Jul 01, 2013 PSLV-C22 Navigation
67 INSAT-3D Jul 26, 2013 Ariane-5 VA-214 Climate & Environment, Disaster
Management System
68 GSAT-7 Aug 30, Ariane-5 VA-215 Communication

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 2013
69 Mars Orbiter Nov 05, PSLV-C25 Planetary Observation
Mission 2013
Spacecraft
70 GSAT-14 Jan 05, 2014 GSLV-D5 Communication
71 IRNSS-1B Apr 04, 2014 PSLV-C24 Navigation
72 IRNSS-1C Oct 16, 2014 PSLV-C26 Navigation
73 GSAT-16 Dec 07, 2014 Ariane-5 VA-221 Communication
74 Crew module Dec 18, 2014 LVM-3/CARE Experimental
Atmospheric Mission
Re-entry
Experiment
(CARE)
75 IRNSS-1D Mar 28, PSLV-C27 Navigation
2015
76 GSAT-6 Aug 27, GSLV-D6 Communication
2015
77 Astrosat Sep 28, 2015 PSLV-C30 Space Science
78 GSAT-15 Nov 11, Ariane-5 VA-227 Communication, Navigation
2015
79 IRNSS-1E Jan 20, 2016 PSLV-C31 Navigation
80 IRNSS-1F Mar 10, PSLV-C32 Navigation
2016
81 IRNSS-1G Apr 28, 2016 PSLV-C33 Navigation
82 CARTOSAT-2 Jun 22, 2016 PSLV-C34 Earth Observation
Series Satellite
83 INSAT-3DR Sep 08, 2016 GSLV-F05 Climate & Environment, Disaster
Management System
84 SCATSAT-1 Sep 26, 2016 PSLV-C35 Climate & Environment
85 GSAT-18 Oct 06, 2016 Ariane-5 VA-231 Communication
86 RESOURCES Dec 07, 2016 PSLV-C36 Earth Observation AT-2A
87 Cartosat -2 Feb 15, 2017 PSLV-C37 Earth Observation
Series Satellite
88 INS-1B Feb 15, 2017 PSLV-C37 / Experimental
Cartosat -2 Series
Satellite
89 INS-1A Feb 15, 2017 PSLV-C37 / Experimental
Cartosat -2 Series
Satellite
90 GSAT-9 May 05, GSLV-F09 / Communication 2017 GSAT-9
91 GSAT-19 Jun 05, 2017 GSLV Mk III- Communication

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 D1/GSAT-19
Mission
92 Cartosat-2 Jun 23, 2017 PSLV-C38 / Earth Observation
Series Satellite Cartosat-2 Series
Satellite
93 GSAT-17 Jun 29, 2017 Ariane-5 VA-238 Communication
94 IRNSS-1H Aug 31, PSLV- Navigation Launch Unsuccessful
2017 C39/IRNSS-1H
Mission
95 Microsat Jan 12, 2018 PSLV- Experimental
C40/Cartosat-2
Series Satellite
Mission
96 INS-1C Jan 12, 2018 PSLV- Experimental
C40/Cartosat-2
Series Satellite
Mission
97 Cartosat-2 Jan 12, 2018 PSLV- Earth Observation
Series Satellite C40/Cartosat-2
Series Satellite
Mission
98 GSAT-6A Mar 29, GSLV- Communication
2018 F08/GSAT-6A
Mission
99 IRNSS-1I Apr 12, 2018 PSLV-C41 Navigation
100 GSAT-29 Nov 14, GSLV Mk III-D2 / Communication
2018 GSAT-29 Mission
101 HysIS Nov 29, PSLV-C43 / Earth Observation
2018 HysIS Mission
102 GSAT-11 Dec 05, 2018 Ariane-5 VA-246 Communication Mission
103 GSAT-7A Dec 19, 2018 GSLV-F11 Communication
Mission
104 Microsat-R Jan 24, 2019 PSLV-C44
105 GSAT-31 Feb 06, 2019 Ariane-5 VA-247 Communication
106 EMISAT Apr 01, 2019 PSLV-C45
107 RISAT-2B May 22, PSLV-C46 Disaster Management System, Earth
2019 Mission Observation
108 Chandrayaan2 Jul 22, 2019 GSLV-Mk III - Planetary Observation
M1 /
Chandrayaan-2
Mission

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Organisation using remote sensing techniques in Agriculture
1. National Remote Sensing Agency (NRSA), Hyderabad
2. Space Application Centre (SAC), Ahmedabad
3. National Bureau of Soil Survey and Land Use Planning (NBSSLUP), Nagpur
4. Central Ground Water Board ( CGWB)
5. National Institute of Oceanography (NIO) and
6. All India Soil and Land Use Survey (AISLS), New Delhi.

Effect of elevated CO2 on C3 and C4 plant

Effect of photosynthesis
C3 plants
The bulk of vegetation belongs to the C3 photosynthesis group. This group is called C3
because the ‘first’ product of carboxylation is a 3-carbon acid, phosphoglyceric acid (PGA).
Out of 15 crops which supply 90 per cent of the world’s calories, 12 have the C3 photosynthetic
pathway. C3 photosynthesis is known to operate at less than optimal CO2 levels and can show
dramatic increase in carbon assimilation, growth and yields. Biomass increase of 10–143 per
cent was observed in several C3 crops in response to doubling of the ambient CO2. A literature
survey on the influence of elevated CO2 among certain C3, C4 and crassulacean acid
metabolism (CAM) species suggests that most of the C3 plants showed a significant positive
response to photosynthetic acclimation, Sorghum and Panicum (two C4 plants) exhibited
negative response, whereas Ananas, Agave and Kalanchoe (CAM plants) showed positive
responses to increased CO2 concentration during growth. The advantage of efficient CO2
assimilation in C3 plants has been related to the availability of increased substrate in the
atmosphere and in the fact that they do not have to bear the metabolic costs of CO2
concentrating mechanism at the site of carboxylation. Photosynthesis in C3 plants is usually
influenced by RuBP (ribulose bisphosphate) carboxylase - oxygenase (rubisco) and by the
accumulation of carbohydrates during carbon assimilation. This activity of the enzyme would
cause the combination of CO2 with RuBP followed by dismutation into two molecules of 3-
PGA, which is known as the first committed step in the Calvin–Benson–Bassham cycle. As
rubisco is substrate-limited by the current atmospheric CO2 levels, this enzyme has the
potential to respond to increases in CO2 concentration; and have a metabolic control to alter
the CO2 flux during carbon assimilation. Elevated CO2 is known to be advantageous to the
kinetic characteristics of rubisco as it increases the velocity of carboxylation and at the same
time competitively inhibits the oxygenase reaction. Most of the studies on pot-grown C3 plants
under elevated CO2 have indicated photosynthetic acclimation, which might be due to soil and
nutrient limitation associated with reduced root volume. However, experiments conducted in
open top chambers (OTCs) and free atmospheric CO2 enrichment (FACE) environment showed
significant increases in light-saturated rates of photosynthesis in several C3 plants grown at
elevated CO2.
The marked increase in net assimilation rates has been explained to be due to increased
intercellular CO2 concentrations (Ci). Increased photosynthetic rates under high CO2 levels
were determined by the activity of rubisco, when RuBP regeneration was not limiting. As
implied above, elevated CO2 atmosphere increases the carboxylation efficiency relative to
oxygenation, resulting in reduced photorespiration. Strong reduction in photosynthetic rates
under elevated CO2 conditions has been associated with reduction in the initial slope of A/Ci
(A, photosynthetic rate and Ci, internal CO2 concentration) response curve due to reduced

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rubisco activity. Decrease in rubisco catalytic activity has been attributed to the repression of
transcription of small subunit gene. The activity of carbonic anhydrase (CA) was also thought
to be crucial in photosynthetic acclimation. CA activities were predicted to enhance the rate of
photosynthesis by catalysing the rapid equilibration of inorganic carbon and thus increasing
the supply of CO2 across the stroma in the chloroplast. CA was low in most of the plants
exposed to elevated CO2, but enhanced CA activities were noticed in Arabidopsis and Zea mays
(maize or corn), grown at elevated CO2, indicating difficulties in the interpretation of the role
of CA in photosynthetic acclimation. However, research on the response of different isoforms
of CA and their polyfunctionality in concentrating CO2 near the carboxylation site should
provide useful evidence for the positive role of CA as a regulator for photosynthetic
acclimation. The role of other enzymes including sucrose phosphate synthase, ADPG
pyrophosphorylase, rubisco activase and phosphoenolpyruvate carboxylase (PEPCase) in
regulating carbon assimilation under elevated CO2 has now received greater attention. Changes
in photosynthetic rates and acclimatory responses in C3 plants grown under elevated CO2
concentration could also be attributed to the feedback metabolic control wherein large
accumulation of foliar starch and other carbohydrates could inhibit CO2 assimilation rates,
whereas the plants with potential sinks for carbohydrate translocation and accumulation may
not show any down regulation of photosynthetic capacity suggesting that imbalances in source–
sink could be attributed to the variations in the photosynthetic acclimation in different plants.
The relationship between carbohydrate accumulation rates and concomitant increase in
respiration in plants under enriched CO2 is still a matter of controversy. Higher dark respiration
rates were recorded in several C3 plants grown in high CO2 environment whereas certain C4
plants did not show any changes in foliar respiration. Further, the reallocation of resources
away from the nonlimiting processes including rubisco into limiting ones might also result in
the acclimation of the photosynthetic apparatus resulting in down-regulation of carbon
assimilation rates under elevated CO2 growth regimes. The role of starch and sucrose
accumulation during photosynthetic acclimation in the leaves grown under elevated CO2 is still
a subject of debate. Some evidence suggests that monosaccharides rather than starch and
sucrose activate the signal for photosynthetic acclimation in plants. A two-season (spring and
summer) experiment conducted on experimental field at the University of Hyderabad
(Hyderabad, India) for three consecutive years (2006–2008), using a tree species Gmelina
arborea Roxb (Verbenaceae) under CO2-enriched atmosphere in open top chambers (4 × 4 × 4
m), demonstrated a significant up-regulation of photosynthesis throughout the growing season.
Plants grown under high CO2 (460 μmol l–1) showed high rates of photosynthesis compared to
those grown under ambient CO2 levels (360 μmol l–1). After the harvest during all seasons, the
biomass yields were markedly higher (48%) in the plants grown under elevated CO2. Unlike
many other reported plant species, growth of Gmelina in elevated CO2 resulted in increased
root volume, stem diameter, altered branching pattern and significant increase in plant height.
We attribute the positive correlation between photosynthesis and the morphological
characteristics of Gmelina to be due to potential sink capacity which is crucial to the
understanding of the physiological, biochemical, genetic and environmental limitations for the
productivity in plants grown in CO2-enriched atmosphere. These potential changes in the
growth and development of Gmelina under elevated CO2 may also be ascribed to increased cell
division, cell expansion, cell differentiation and organogenesis, stimulated by increased carbon
and more efficient water use. Optimal utilization of resources and well-balanced source–sink
activity might enhance carbon gain in plants grown under elevated CO2. However, the ability

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of exploiting the extra carbon by any plant species might largely be a function of its inherent
structural and physiological attributes, integrated with the plasticity of morphological and
anatomical characteristics. Other factors which can influence plant responses to elevated CO2
are the growth environment, soil nutrition and the genetic organization of the plant species.
The direct effects of rising CO2 on plant growth and metabolism are a modulation of stomatal
conductance, changes in carboxylation capacity, and accumulation of photo assimilates. Davey
et al. postulated that fast growing perennial species would have a greater advantage of having
a better sink strength which could result in the upregulation of carbon metabolism unlike the
annual species wherein photosynthetic acclimation has been frequently recorded due to less
efficient sink capacity. Different experiments on the effects of elevated CO2 on photosynthetic
capacity in C3 plants indicate either up- (or) down-regulation, which varies with genetic and
interactive environmental factors.
C4 plants
Most of the research on plant responses to elevated CO2 has been carried out with C3
species, whereas C4 plants have received very little attention. These plants are called C4 plants
because the ‘first’ product of carboxylation is a 4-C acid (e.g. malic acid); the C-4 pathway, is
also called the Hatch–Slack pathway. The lower attention on C4 plants in the studies of the
effects of increased CO2 has been attributed to the assumption that the inherent CO2
concentrating mechanism in C4 plants renders these plants insensitive to elevated CO2
atmosphere. Under natural atmospheric conditions, the biochemistry of C4 photosynthesis
elevates CO2 concentration in the bundle sheath cells approximately to 2100 μmol l–1, which
is at least 10 times more than that present in the mesophyll cells of the C3 plants. This
substantially higher CO2 level saturates the carboxylase reaction and abolishes
photorespiration. Moreover, photosynthesis in C4 plants is more readily saturated at the normal
atmospheric CO2 concentrations, which reflects that PEPcase (phosphoenolpyruvate.
carboxylase) is insensitive to changes in the ratio of CO2 : O2 due to lack of binding of O2 to
the catalytic site of PEPcase. However, several reports indicate that C4 plants also significantly
respond to elevated CO2 concentration by showing enhanced carbon uptake. Some C4 plants
grown under FACE (free-air CO2 enrichment) exhibited increased photosynthetic rates only
during drought or under the conditions of atmospheric vapour pressure deficits. Ghannoum et
al. reported that C4 plants, grown under high irradiance, showed enhanced photosynthesis
under elevated CO2 conditions, whereas there was not much response in the growth of C4
species under low irradiance. Doubling of the current ambient CO2 concentration stimulated
the growth of C4 plants to the tune of 10–20 per cent whereas that in C3 plants was about 40–
45 per cent. It is also well known that the growth stimulation of C4 weeds is much larger
compared to that of C4 crops. Although certain C4 plants showed positive response to elevated
CO2, the underlying mechanisms for the enhanced growth responses are still not clear. In
addition to improved photosynthetic rates under elevated CO2, C3 plants exhibited reduced
mitochondrial respiratory rates, which could contribute to increased biomass yield. However,
little is known about the impact of elevated CO2 on the respiratory rates of C4 plants. The
positive responses of certain C4 plants to elevated CO2 were believed to be due to differences
in bundle sheath leakiness, biochemical subtype, and direct CO2 fixation in the bundle sheath
cells as well as C3-like photosynthesis in young and developing leaves of C4 species. Further,
the lack of photosynthetic acclimation in C4 plants
(in contrast to several C3 plants) could be attributed to relatively less rubisco protein and more
active carbonic anhydrase and PEPcase. Although there are several studies on the interactive

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effects of increased air temperature, nutrients, water availability and elevated CO2, very little
is known about such interactive influence of elevated CO2 with the environmental variables
during growth of C4 plants.
Crassulacean acid metabolism
CAM photosynthesis is known to occur in approximately 7 per cent of the vascular
plants. CAM is one of the three types of photosynthesis used by vascular plants in which
nocturnal CO2 fixation results in the formation of malate (a salt or ester of malic acid), which
is decarboxylated during day time releasing CO2, which in turn is assimilated into
carbohydrates. Compared to the studies on the effects of elevated CO2 in C3 and C4 plants, very
little is known about the response of CAM plants to increasing atmospheric CO2
concentrations. CAM plants are known for their considerable inherent photosynthetic plasticity
associated with environmental conditions during different developmental stages. The
characteristic features of nocturnal CO2 fixation in CAM plants and variation in responses of
carboxylating enzymes (both rubisco and PEPcase) make generalization of their response more
complex than those of C3 and C4 plants. Although certain CAM plants show stimulated rates of
photosynthesis and 20–40 per cent increase in biomass production, under elevated atmospheric
CO2 concentrations, with no acclimation during growth, contradictory range of responses of
these plants to elevated CO2 have been reported, which include increase and/or decrease in
nocturnal CO2 uptake, daytime CO2 fixation patterns as well as in water use efficiency. The
lack of acclimation in CAM plants under elevated CO2 has been attributed to the succulence
which could be a diffusional constraint to CO2 as well as to accommodate large amount of
photosynthate to avoid feedback inhibition. The significant increase in biomass production in
CAM plants under elevated CO2 atmosphere, on marginal arid and semi-arid lands, suggests
that CAM plants could also be exploited for terrestrial sequestration of atmospheric CO2 in the
changing global environment. Further, the exceptional degree of stress tolerance in CAM plants
to water-deficit regimes, high temperatures and high light intensities should render these plants
robust to the predicted harsh impacts of the future global climate change. The lack of
acclimation of CAM species under elevated atmospheric CO2 concentrations could enhance
the importance of several economically important CAM plants worldwide in improving the
photosynthetic productivity.
Interactions between elevated CO2 and other environmental factors
The majority of the experiments demonstrate positive response to elevated CO2 when
grown under controlled conditions. The positive response was primarily due to improved
photosynthetic rates which were associated with increased biomass yields. The relative
importance of other factors including water availability, soil nutrition, temperature, relative
humidity and ozone, which could possibly interact with the effects of elevated CO2, need to be
understood.
Temperature: Available literature indicates that semi-arid plants will greatly benefit from a
rise in the atmospheric CO2 concentration, such crops show greater percentage increase in yield
under elevated CO2. C3 plants exhibit stimulated rates of photosynthesis with increase in
temperature under elevated atmospheric CO2 concentration. Theoretical calculations on the
interactive effects of elevated CO2 concentration and temperature were based on the
carboxylation to oxygenation ratios. Such studies confirm that the predicted positive CO2
uptake may be increased by an increase in the temperature at least by 2–4°C at elevated
atmospheric CO2 concentration. The light-saturated rates of photosynthesis under elevated CO2
concentrations in FACE (free-air CO2 enrichment) experiments were enhanced by 19 per cent

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at 25°C and below, whereas, above 25°C showed 30 per cent increase in photosynthetic rates.
High temperatures might also affect/alter the carbon utilization rates of the fast growing
metabolic sinks, reducing carbohydrate accumulation, which in turn enhances the up regulation
of photosynthesis under high CO2. High (36°C) and low (18°C) temperatures are known to
reduce carbohydrate export through phloem resulting in downward acclimation in CO2
enriched atmosphere. However, the actual consequences of rise in temperature (above 35°C),
associated with increase in atmospheric CO2 concentration, are difficult to predict as these
interactive effects are still to be established in combination with other environmental variables
including drought stress and nutrient availability.
Soil nitrogen: Nitrogen (N) is required in relatively very large quantities for growth and
development of plants, especially for plants grown under elevated CO2 atmosphere. Plant N
productivity (g dry weight increase per unit plant N content) is known to increase under
elevated CO2 to sustain the photosynthetic rates similar to those observed at ambient CO2, but
with a reduced investment in leaf N. Rubisco acclimation in plants grown under elevated CO2
results in substantial saving in leaf N, which would be greater in crop species compared to tree
species. FACE (free-air CO2 enrichment) experiments have proven that plants grown with low
N accumulate more foliar carbohydrates associated with greater rubisco acclimation compared
to those grown with high N supply. Perhaps, more N is to be provided for the plants grown
under elevated CO2 to offset the N-limited biochemical events. A recent analysis showed a
positive interaction between elevated CO2 and N, indicating that limitation of soil N might
progressively suppress the positive responses in photosynthetic carbon acquisition and biomass
to elevated CO2. Such limitation of CO2 fertilization under reduced N availability may not be
noticed under N-rich soils. Most of the elevated CO2 studies have considered soil N as the
limiting factor with relatively less attention to other essential mineral nutrients. Possible
molecular reprogramming/genetic manipulation of N use efficiency under excess sugar
environment would be highly favourable to plants grown under elevated CO2. For example,
genetic manipulation of nitrogen metabolism, specifically over-expression of rate limiting
enzymes of nitrogen assimilation, could improve the capacity of nitrogen sink for overloaded
sugar. Further research is needed to establish the role of other nutrients to understand the
mechanisms of their effects on the acclimation of plants under elevated CO2. Photosynthetic
acclimation to elevated CO2 would be more pronounced under nutrient-limited conditions
whereas adequate nutrient supply is believed to mitigate the elevated CO2- mediated
acclimation, at least in crop species.
Water availability: Interactive studies on water availability and elevated CO2 show that there
will be a partial closure of stomata due to increased CO2 concentration in the sub stomatal
cavity decreasing partial pressure of CO2 in the leaf and this CO2-dependent amplification of
stomatal response could improve water use efficiency at the leaf and whole plant level. In a
wide range of experiments, plants grown under elevated CO2 had substantial decrease in
stomatal conductance (gs) showing acclimation of gs to elevated CO2. Decreased gs might
increase leaf temperature, which could increase the rates of transpiration. However, plants
grown under elevated CO2 possessed increased root surface and root volume due to increased
allocation of carbon to root growth. Such increase in the surface area of roots enables the plants
grown under elevated CO2 to exploit more water even from deep soil layers. However, the
decrease in stomatal conductance may also be offset by increased leaf area in plants grown
under elevated CO2 and thus water use by the whole plant may not be proportional to stomatal
conductance. For the actual determination of water use efficiency in plants under

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CO2enrichment, rates of transpiration on plant basis and/or on ground area basis are essential.
It is believed that decreased stomatal conductance is an interactive factor and low water
availability might be beneficial for plant productivity under increased CO2 concentration in the
atmosphere. The availability of water as an interactive environmental factor suggests that the
reduced leaf level stomatal conductance under elevated CO2 might also influence the whole
canopy conductance to water than mitigating the water loss and conserving the available soil
moisture.

Change in secondary metabolite and pest disease reaction

Plants possess capacity to synthesize different organic molecules called secondary

metabolites. Unique carbon skeleton structures are basic properties of plant secondary
metabolites. Secondary metabolites are not necessary for a cell (organism) to live, but play a
role in the interaction of the cell (organism) with its surroundings, ensuring the continued
existence of the organism in its ecosystems. Formation of SMs is generally organ, tissue and
cell specific and these are low molecular weight compounds. These compounds often differ
between individuals from the same population of plants in respect of their amount and types.
They protect plants against stresses, both biotic (bacteria, fungi, nematodes, insects or grazing
by animals) and abiotic (higher temperature and moisture, shading, injury or presence of heavy
metals). SMs are used as especially chemical such as drugs, flavours, fragrances, insecticides,
and dyes by human because of a great economic value.
In plants, SMs can be separated into three groups (Terpenoids, Polyketides and
Phenypropanoids) based on their biosynthesis origin. Alkaloids are additional class of SMs,
which are nitrogenous organic molecules biosynthesized mainly from amino-acids, e.g.,
tryptophan, tyrosine, phenylalanine, lysine and arginine using many unique enzymes. Many of
the most important therapeutic agents are alkaloids. The sites of biosynthesis are
compartmentalised at cellular or sub-cellular level. However SMs can be transported long
distances and accumulate from their location of synthesis.

Primary Vs Secondary Metabolites:

Secondary metabolites are the molecules that appear to be dispensable for normal
growth, or are required only under particular conditions, whereas primary metabolites
are involved in the physiological functions. Primary metabolites are found in all plants and
execute vital metabolic responsibilities, by participating in nutrition and reproduction.
Sometimes it is hard to discriminate primary and secondary metabolites. For example, both
primary and secondary metabolites are found among the terpenoids and the same compound
may have both primary and secondary roles. Secondary metabolites are broad range of
compounds from different metabolite families that can be highly inducible in stress conditions.
Carotenoids and flavonoids are also involved in cell pigmentation in flower and seed, which
attract pollinators and seed dispersers. Therefore, they are also involved in plant reproduction.
Plant primary products refer to the compounds of nucleic acids, proteins, carbohydrates, fats
and lipids and are related to structure, physiology and genetics, which imply their crucial role
in plant development. In contrast, secondary metabolites usually take place as minor
compounds in low concentrations. Primary metabolism refers to the processes producing the
carboxylic acids of the Krebs cycle. Secondary metabolites, on the other hand, are non-essential

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to life but contribute to the species’ fitness for survival. In fact, the specific constituents in a
certain species have been used to help with systematic determination, groups of secondary
metabolites being used as markers for botanical classification (chemotaxonomy). Plants
secondary metabolites can be divided into three chemically distinct groups viz: Terpenes,
Phenolics, N (Nitrogen) and S (sulphur) containing compounds.
I) Terpenes: Terpenes comprise the biggest group of secondary metabolites and are free by
their common biosynthetic origin from acetyl-coA or glycolytic intermediates. An immense
bulk of the diverse terpenes structures produced by plants as secondary metabolites that are
supposed to be concerned in defence as toxins and feeding deterrents to a large number of plant
feeding insects and mammals. Terpenes are divided into monoterpenes, sesquiterpenes,
diterpene, Triterpenes and polyterpenes. The pyrethroid (monoterpenes esters) occur in the
leaves and flowers of Chrysanthemum species show strong insecticidal responses to insects
like beetle, wasps, moths, bees, etc and a popular ingredient in commercial insecticides because
of low persistence in the environment and low mammalian toxicity. In Gymnoperms (conifers)
á-pinene, â-pinene, limonene and myrecene are found. A number of sesquiterpenes have been
till now reported for their role in plant defence such as costunolides are antiherbivore agents of
family composite characterized by a five member lactone rings (a cyclic ester) and have strong
feeding repellence to many herbivorous, insects and mammals. ABA is also a sesquiterpene
plays primarily regulatory roles in the initation and maintenance of seed and bud dormancy
and plants response to water stress by modifying the membrane properties and act as a
transcriptional activator. Abietic acid is a diterpene found in pines and leguminous tress. It is
present in or along with resins in resin canals of the tree trunk. Another compound phorbol
(Diterpene ester), found in plants of euphorbiaceae and work as skin irritants and internal toxins
to mammals. The milkweeds produce several better tasting glucosides (sterols) that protect
them against herbivores by most insects and even cattle. Several high molecular weight
polyterpenes occur in plants. The principal tetraterpenes are carotenoids family of pigments.
(II) Phenolic compounds: Plants produce a large variety of secondary products that contain
a phenol group, a hydroxyl functional group on an aromatic ring called Phenol, a chemically
heterogeneous group also. They could be an important part of the plants defence system against
pests and disease including root parasitic nematodes. Elevated ozone (mean 32.4ppb) increased
the total phenolic content of leaves and had minor effects on the concentration of individual
compounds. Coumarin are simple phenolic compounds widespread in vascular plants and
appear to function in different capacities in various plant defence mechanisms against insect
herbivores and fungi. They derived from the shikimic acid pathway, common in bacteria, fungi
and plants but absent in animals. Some coumarin derivatives have higher antifungal activity
against a range of soil borne plant pathogenic fungi and exhibit more stability as compared to
the original coumarin compounds alone. Furano is also a type of coumarin with special interest
of phytotoxicity, abundant in members of the family umbelliferae including celery parsnip and
parsley. Psoraline, basic linear furacoumarin, known for its use in the treatment of fungal
defence and found very rarely in SO2 treated plants. Ligin is a highly branched polymer of
phenyl- propanoid groups, formed from three different alcohols viz., coniferyl, coumaryl and
synapyl which oxidized to free radical (ROS) by a ubiquitous plant enzymeperoxidises, reacts
simultaneously and randomly to form lignin. Its physical toughness deters feeding by
herbivorous animals and its chemical durability makes it relatively indigestible to herbivorous
and insects pathogens. Lignifications block the growth of pathogen and are a frequent response
to infection or wounding. Flavanoids perform very different functions in plant system including

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pigmentation and defence. Two other major groups of flavanoids found in flowers are
flavanones and flavanols function to protect cell from UV-B radiation because they accumulate
in epidermal layers of leaves and stems and absorb light strongly in the UV-B region while
letting visible (PAR) wavelengths throughout uninterrupted. In addition exposure of plants to
increased UV-B light has been demonstrated to increase the synthesis of flavanones and
flavanols suggesting that flavanoids may offer measures of protection by screening out harmful
UV-B radiation. Isoflavanoids are derived from a flavanones intermediate, naringenin,
ubiquitously present in plants and a play a critical role in plant developmental and defence
response. They secreted by the legumes and play an important role in promoting the formation
of nitrogen fixing nodules by symbiotic rhizobia. Moreover, it seems that synthesis of these
flavanoids is an effective strategy against reactive oxygen species (ROS). The analysis of
activity of antioxidant enzymes like SOD, CAT, POX, APX, GPX and GR suggested that
peroxidases were the most active enzymes in red cabbage seedlings exposed to Cu++ stress.
Tannins included in the second category of plant phenolic polymers with defensive properties.
Tannins are general toxins that significantly reduce the growth and survivorship of many
herbivores, and also act as feeding repellents to a great diversity of animals.
(III) Sulphur containing secondary metabolites: They include GSH (Glutathione), GSL
(glucan synthase), Phytoalexins, Thionins, defensins and allinin which have been linked
directly or indirectly with the defence of plants against microbial pathogens. GSH is the one of
the major form of organic sulphur in the soluble fraction of plants and has an important role as
a mobile tool of reduced sulphur in the regulation of plant growth and development and as a
cellular antioxidants in stress responses, reported as a signal of plant sulphur sufficiency that
down regulates sulphur assimilation and sulphur uptake by roots. GSL is a group of low
molecular mass N (nitrogen) and S (sulphur) containing plant glucosides that produced by
higher plants in order to increase their resistance against the unfavourable effects of predators,
competitors and parasites because their break down products are release as volatiles defensive
substances exhibiting toxic or repellent effects for example, mustard oil glucosides in
cruciferae and allyl cys sulfoxides in alllum. They are metabolised and absorbed as
isothiocyanates that can affect the activity of enzymes involved both in the antioxidant defence
system and in the detoxification from zenobiotics abd significantly affect GST activity and cell
protection against DNA damage whereas toxicity of glucosinolatic products is well
documented but their mode of action has not yet been elucidated and results from experiments
with Brassica plants modified in GSL content generated doubts about their contribution to plant
defences. Phytoalexins are synthesized in response to bacterial or fungal infection or other
forms of stress that help in limiting the spread of the Secondary Metabolites of Plants and their
Role invading pathogens by accumulating around the site of infection, appears to a common
mechanism of resistance to pathogenic microbes in a wide range of plants. Many of these
changes are linked to a rapid apoptotic response, resulting in death of one or a few invaded
plant cells, known as the hypersensitive response (HR). Most plant families produce organic
phytolexins of diverse chemistry; these groups are often associated with a family, for example
sesquiterpenoids of Solanaceae, isoflavonoids of Leguminosae, while phytoalexins from
Brassica have an indole or related ring system and one S atom as common structural features.
Crucifereae appears to be the only plant family producing these S metabolites, which are clearly
different from the other well- known GSL. Cruciferous crops are cultivated worldwide because
they are extremely valuable and for the last decades, various research groups have investigated
cruciferous phytoalexins as well as their biological activity. Typically, there are multiple

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responses involving several related derivatives such as up to nine wyerone (Furano-acetylenic
derivatives) forms in Vicia fava and several forms of phaseollin in Phaseolus vulgaris and
glyceollin in Glycine max, postin in Pisum sativum pods, Ipomearone in sweet pototo, orchinol
in orchid tubers, trifolirhizin in red clover. Defensins, thionins and lectins are S-rich non-
storage plant proteins synthesize and accumulate after microbial attack and such related
situations. They inhibit growth of a broad range of fungi. Additionally defensins genes are
partly pathogeninducible and others that are involved in resistance can be expressed
constitutively. Some plant species produce lectins as defensive proteins that bind to
carbohydrates or carbohydres containing proteins.
(IV) Nitrogen containing secondary metabolites: They include alkaloids, cyanogenic
glucosides, and non-proteins amino-acids. Most of them are biosynthesized from common
aminoacids. Alkaloids found in approximately 20 per cent of the species of vascular plants,
most frequently in the herbaceous dicot and relatively a few in monocots and gymnosperms.
Generally, most of them, including the pyrrolizidine alkaloids (PAs) are toxic to some degree
and appear to serve primarily in defense against microbial infection and herivoral attack.
Cyanogenic glucosides constitue a group of N-containing protective compounds other than
alkaloids, release the poison HCN and usually occur in members of families viz., Graminae,
Roosaceae and leguminosesae. They are not themselves toxic but are readily broken down to
give off volatile poisonous substance like HCN and volatile H2S when the plant crushed; their
presence deters feeding by insects and other herbivorous such as snails and slugs. Amygdalin,
the common cynogenic glucoside found in the seeds of almonds, apricot, cherries and peaches
while Dhurrin, found in Sorghum bicolar. Many plants also contain unusual amino acids called
non-protein amino-acids that incorporated into proteins but are present as free forms and act as
protective defensive substance. For examples, canavanine and azetidine-2 carboxylic acid are
close analogs of arginine and proline respectively. They exert their toxicity in various ways.
Some block the synthesis of or uptake of protein amino acid while others can be mistakenly
incorporated into proteins. Plants that synthesized non-protein amino acid are not susceptible
to the toxicity of these compounds but gain defence to herbivorous animals, insects and
pathogenic microbes.
Functions of Secondary Metabolites: Many secondary compounds have signalling functions
influence the activities of other cells, control their metabolic activities and co-ordinates the
development of the whole plant. Other substances such as flower colours serve to communicate
with pollinators or protect the plants from feeding by animals or infections by producing
specific phytoalexines after fungi infections that inhibit the spreading of the fungi mycelia
within the plant. Plants use secondary metabolites (such as volatile essential oils and colored
flavonoids or tetraterpenes) also to attract insects for pollination or other animals for seed
dispersion, in this case secondary metabolites serve as signal compounds. Compounds
belonging to the terpenoids, alkaloids and flavonoids are currently used as drugs or as dietary
supplements to cure or prevent various diseases and in particular some of these compounds
seem to be efficient in preventing and inhibiting various types of cancer. It has been estimated
that 14- 28 per cent of higher plant species are used medicinally and that 74 per cent of
pharmacologically active plant derived components were discovered after following up on
ethno-medicinal use of the plants. Secondary metabolites are a metabolic intermediates or
product, found as a differentiation product in restricted taxonomic groups, not essential to
growth and life of the producing organism and biosynthetized from one or more general
metabolites by wider variety of pathways than is available in general metabolism.

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 Presence of volatile monoterpenes or essential oils in the plants provides an important
defence strategy to the plants, particularly against herbivorous insect pests and pathogenic
fungi. These volatile terpenoids also play a vital role in plant-plant interactions and serve as
attractants for pollinators. They act as signalling molecules and depict evolutionary relationship
with their functional roles. Soluble secondary compounds such as cyanogenic glycosides
isoflavoids and alkaloids can also be toxic to animals.

The mechanisms of ozone and UV damage and tolerance in plants:

Ozone damage:
Most of the ozone in the atmosphere is located in the stratosphere, where ultraviolet light
triggers the production of ozone by dissociation of oxygen. Ozone levels in the troposphere are
much lower but are still sufficiently high to threaten agricultural crops, trees and native plants.
The level of ozone in the troposphere is controlled by a complex set of photochemical reactions,
which produce or destroy ozone, and by the vertical and horizontal transport of air.
Owing to the variability of sources and sinks, ground-level ozone concentrations
fluctuate in space and time. The diurnal pattern varies with altitude; at low elevation sites,
ozone declines during the night. Provided that thermal stratification of the atmosphere leads to
stable nocturnal layers with virtually no ozone exchange between them, ozone concentrations
near the ground can decrease to zero. In urban air, this decline can be attributed to the
destruction of ozone by reaction with nitric oxide and the absence of nitrogen dioxide
photolysis, whereas at rural sites nitric oxide concentrations are small and dry deposition
dominates the removal of ozone. During the day, the surface air is well coupled to the bulk of
the mixing layer by turbulent transfer, and ozone concentrations near the ground increase owing
to the downward transport of ozone from higher levels. In the absence of the stabilityrelated
processes, diurnal variations of ozone are less pronounced, i.e. over rough surfaces such as
forests, or in the presence of strong winds or overcast skies. Highest boundary layer
concentrations normally occur during the afternoon, when photochemical ozone production is
most active. At higher elevations, the diurnal variation is dampened because of the absence of
thermal stratification of the atmosphere, and ozone levels remain high during the night. Hence,
sites with different local features experiencing the same regional ozone distribution may have
different exposure levels, and thus different effects.
Long-term exposure to ozone can lead to growth and yield reduction. Hence the most
suitable exposure indices to be related to long-term effects are cumulative, i.e. they integrate
exposure over time. Previous air quality guidelines for long-term effects have been based on
mean concentrations over a given period of time, e.g. the arithmetic mean over the growing
season of the daily mean concentrations during a specific 7-hour period (usually 09.00–16.00
hours). The use of a mean concentration over a given period of time implicitly gives equal
weight to all concentrations.
Effects of ozone: Effects of ozone may occur at various levels of organization, i.e. from the
cellular level through the level of individual organs and plants to the level of plant communities
and ecosystems. The best documented ozone-induced ecosystem effect is the degradation of
forests in southern California. Today, there is also evidence, mainly from controlled
experiments in Europe and from field and laboratory studies in Canada and the United States,
showing that ozone affects the health and production of forests in these parts of the world. The
magnitude of the effect of ozone on forests, however, is still not quantified. Effects on crops
are much better understood. Results from crop loss networks in the United States and Europe

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have provided exposure - response relationships for a range of crop species, although because
of differences in experimental conditions results from the two networks cannot always be
directly compared. After passing through the stomatal pore, ozone can react with organic
molecules (e.g. ethylene, isoprene) in the intercellular air space or with components of the
extracellular fluid. In both cases, secondary oxidants (e.g. primary ozonides,
hydroxyhydroperoxides) may be formed, which in turn could react with the protein component
of the cell membrane. This reaction is prevented to some extent by the presence of radical
scavengers, such as ascorbic acid and polyamines. Formaldehyde, formate and acetate
accumulate in damaged tissue, possibly as a result of the reaction between ozone and ethylene
or between ozone and the phenylpropanoid residues of lignin.
There is evidence that ethylene formation determines the sensitivity of plants to ozone.
High levels of ozone cause target cells to collapse, leading to local visible tissue destruction.
The effect on the plasma membrane can cause changes in membrane functions that may affect
the internal concentrations of ions (e.g. Ca2+). This changes the osmotic potential of the
cytoplasm, which in turn can reduce photosynthetic processes in the chloroplasts. Reduction in
carbon dioxide fixation by the enzyme ribulosebisphosphate carboxylase is a typical symptom
found in leaves exposed to ozone over longer periods of time. Further inhibition of carbon
dioxide assimilation results from direct or indirect inhibition of stomatal opening that reduces
uptake. Stimulated dark respiration often occurs together with reduced photosynthesis,
probably due to increased respiration associated with maintenance and repair. The combined
effects of reduced assimilation and increased respiratory loss of carbon dioxide consist of an
overall reduction of assimilate production and export from the source leaves. In the leaves of
crop species exposed long term, the onset of senescence is advanced, and accelerated catalysis
leads to the rapid loss of protein and chlorophyll. As a result of the reduction in leaf duration,
the period with positive net assimilation of carbon dioxide is diminished, and the overall
production of assimilates declines. Under conditions of reduced assimilate supply through
photosynthesis, allocation of carbon to different organs may be altered, leading to altered
growth responses of these organs. Typically, higher priority is given to the shoot relative to
roots and/or other storage organs (e.g. seeds). This results in reduced root : shoot weight ratios
or in a reduction of the ratio between seed yield and total biomass production. In agricultural
crops, this results in reduced grain or seed yield. Reduced assimilate supply may also restrict
the plant’s ability to tolerate additional stresses, such as stress due to drought or low
temperatures.
The most important impact of ozone on plant communities may not be through an
impact on growth or productivity, or through visible injury, but through shifts in species
composition, loss of biodiversity, and changes in genetic composition. Several studies of
mixtures of herbaceous species have demonstrated a shift in the relative proportions of the
species in response to ozone, although this is not always accompanied by effects on the total
growth of the mixture. This is to be expected where species are actively competing, since any
reduction in the performance of one species will provide opportunities for other, less sensitive
species, although it is also possible that direct allelopathic effects are involved. In frequently
cut, managed pasture, clover growth was repressed by long-term ozone exposure, whereas the
growth of the relatively resistant grass species was enhanced, possibly because of improved
resource availability (e.g. light).
The longer-term effects of ozone on species composition are uncertain, although field
studies in the San Bernadino Mountains of California have shown that sensitive tree species

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have been eliminated and replaced by other, less sensitive, tree or shrub species. There have
been relatively few studies of growth responses of individual plants of native herbaceous
species, but these do indicate that some European species are very sensitive to ozone. There is
also limited evidence of evolution of resistance to ozone in field populations; this could have
potentially detrimental effects on the population if it were accompanied by a significant loss of
genetic variation, although there is no concrete evidence of this.
Reproductive success is crucial to the survival of populations of many annual plants.
There is some evidence of complete loss of flower production at relatively low ozone
concentrations, while pollen may also be sensitive to ozone.

UV damage and tolerance in plants

Common Sources of UVR
The natural source of UV rays is the sun, while man‐made sources include UV lamps,
and welding instruments are also producers of UV radiation.
Sunbeds: these are designed to produce a tan by emitting UVA and some UVB. Regular use of
a sunbed may contribute significantly to a person’s annual UV skin exposure. The use of eye
protection, such as goggles or sunglasses, is mandatory. Working staff in tanning salons also
be exposed to UV‐B light.
Medical exposure: in some medical and therapeutic diagnostics, UV lights are used.
Exposures vary considerably, according to the type of treatment.
Industrial/commercial exposures: the most significant source of potential exposure is
welding. The levels of UV around welding equipment are very high, and the potential for acute
injury to the eye and the skin is great. Skin and eye protection is compulsory for this work.
Many industrial and commercial processes involve the use of UV‐producing lamps. While the
probability of harmful exposure is low, because of protection provided with the lamp, unusual
exposure can occur in some cases.
Lighting: fluorescent lamps are common in the workplace, and are often used in the home.
These lamps emit small amounts of UV, and typically contribute only a few percent to a
person’s yearly UV exposure. Halogen lamps, made of tungsten, are increasingly used in the
home and in the workplace for a variety of lighting and display purposes. Uncovered lamps
can emit UV radiations sufficient to cause acute injury at short distances. UV filters on the
lamps can considerably reduce these radiations. Black lights, which emit mainly UVA, are
frequently used for special effects (e.g. in discotheques), and also for the authentication of bank
notes and documents. These lamps have not caused significant UV exposure to humans.
Classification
UV radiation falls into three types, on the basis of wavelength and intensity:
1) UV‐A (315–400 nm) are less absorbed by the stratospheric ozone layer. The maximum
part of UV‐A radiation is able to reach the earth’s surface, and can cause tanning, skin aging,
eye damage, and immune suppression in animals; while, in plants, it can influence plant
morphology, plus some specific effects (e.g. stomatal opening and induction of pigment
formation).
2) UV‐B (280–315 nm) is strongly absorbed by the ozone layer but, if it reaches the earth’s
surface, it can contribute to snow blindness, sunburns, immune reductions and a variety of skin
problems, including skin cancer and premature aging. In plants, it induces many
morphological, physiological and molecular changes, including leaf structure alteration,
antioxidative machinery and DNA damage.

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3) UV‐C (100–280 nm) is completely absorbed by the ozone layer, so that the levels of
UV‐C radiation reaching the earth’s surface are very small. However, it is lethal in nature and
can change the expression pattern of genes in animals as well as in plants. Artificial UV‐C can
cause severe damage to exposed tissues.

Environmental Factors Affecting UV Level

Sunlight: diurnal variations and seasonal variations both have an impact on UV radiation
levels.
Latitude: at lower latitudes, exposure to UV radiation is much higher.
Cloud cover: UV levels are mostly less in a cloudy sky, but sometimes they may be high, due
to scattering of UV radiation through water molecules and tiny particle present in the clouds.
Altitude: for every 1000 metres increase in elevation, UV levels increase by 10–12 per cent.
Stratospheric ozone: all UV‐C, and 90% of the UV‐B radiations, are absorbed by the ozone
layer, water vapour, and carbon dioxide. UV‐A radiation is less absorbed by the atmosphere.
Hence, the UV radiation reaching the earth’s surface is largely composed of UV‐A, with a small
quantity of UV‐B.

Effects of UV-B on Plants

Depletion of ozone layer leads to the increase in ultraviolet radiation (UV-B) reaching
to the Earth surface. Increase of UV-B radiation will alter the growth and metabolism of plants,
thus UV-B radiation acts as an environmental stress/ abiotic factor on plants, which ultimately
causes the slowing of plant growth, damages the photosynthetic pigments, lowers the carbon
assimilation, altering the biomass allocation ultimately results in reduction of biomass and
productivity.
All the plants show various responses to UV-B, some plants can tolerate this stress and
some becomes sensitive and cannot tolerate such situation. These plants will acquire different
defence mechanisms like increased thickness of leaves, production of more flavonoids,
stimulation of the antioxidant formation; activation of the reactive species to quench free
radicals, etc to protect the plants from such kind of environmental stresses. Rise in UV-B
radiation in the environment results into different physiological responses. Changes observed
after supplemental UV-B radiation includes epidermal deformation, changes in stomatal
conductance, changes in ultra-structure of leaves, increased level of flavonoids, reduction in
percentage of pollen germination, biomass reduction. These changes could be the result of
DNA damage, photosynthetic damage, alteration in membrane, destruction of protein, hormone
inactivation, and signal transduction through phytochrome (which photoconverts in response
to UV-B)(Pratt and Butler, 1970), or signal transduction via a UVB photo receptor.
Morphological changes induced by UV-B: Morphology of plants is considered to be a very
effective indicator of UV-B damage. Measurements of other parameters like chlorophyll,
carotenoids, phenols, lipid peroxidation, etc. have also proved to be useful indicators of UV-B
tolerance and sensitivity. And these changes includes from increase in leaf thickness,
discoloration of leaves, increase in leave serration to changes in root-shoot ratio. As a result of
UV-B stress, initially browning, cupping, glazing of leaves are observed which is followed by
development of irregular patches and with prolonged exposure, these patches gets converted
into brown spot and dies. Zhao et al. (2003) has reported that these chlorotic and necrotic spots
are formed due to decrease in chlorophyll content. It was also reported that leaf size decreases,
leading to less leaf area and lesser branches, extension rate of stem also declines but sometimes

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opposite trends was observed like intense branching, more number of internodes, increased
plant height and dense canopy. Exposure to UV radiation also leads to increase in cuticular wax
deposition.
Kakani et al. (2003) had reported that prolonged exposure of UV-radiation leads to
delayed flowering in different crops; opposite to that Sinclair et al. (1990) has told that early
bud or flower development or time of first flower is not affected by UV-B.
Broad leaf plants are more sensitive in comparison to narrow leaf plants. Moreover, the
members of family Cucurbitaceae and Brassicaceae are more sensitive. Increased level of UV-
B also induces some common morphological changes such as reduction in leaf area, thickening
of the leaves, curling or cupping of the leaves, increases in branching, tillering and number of
leaves, decreases in number of fruits and flowers and seedling.
Reduction in leaf area occurs due to destruction of photosynthetic pigments but to cope
up with the situation and to increase photosynthesis, number of leaves increases into the
affected plants, which ultimately leads to increased number of branching in dicots and
increased number of tillers in monocots. Most of the energy is lost in repair mechanisms,
leading to the reduction in flowering and fruiting. Moreover, thickening of leaves are a defence
mechanism acquired by the plants in order to increase the path length of UV radiation. Due to
conversion of Indole-acetic-acid into 3-methylene oxindole curling of leaves takes place. By
this conversion, less growth of the upper side and normal growth of the lower side of the leaves
take place, this ultimately causes the cupping of leaves.
Physiological changes induced by UV-B: The process of conversion of CO2 and water
into carbohydrate in the presence of sunlight is termed as “Photosynthesis”. Photosynthetic
apparatus is comprised of two photosystems: PS-I and PS-II. Although UV-B encroaches most
of the aspects of photosynthesis such as damages to ultra-structure of chloroplast and light
harvesting complex, decrease in the activity of Rubisco, decline in the oxygen evolving and
CO2 fixation, reduction in the chlorophyll and starch content. And the photosynthetic responses
of plants towards UV-B radiation depend on plant species, cultivars, experimental conditions,
UV-B dosage, and the ratio of PAR to UV-B radiation. But the main target of UV-B is PS-II.
PS-II is a complex of protein and pigment which transports the flow of electron(s) from
splitting of water to plastoquinones. PS-II is comprised of two proteins, namely D1 and D2,
which forms the core of PS-II. These two proteins are very sensitive against UV-B and UV-B
driven degradation of D1 and D2 protein leads to impairment of PSII, which can be measured
in terms of decreased oxygen evolution or variable chlorophyll florescence. Almost all
components from Mn binding sites to plastoquinone acceptor sites within PS-II on thylakoid
membrane are sensitive against UV-B. In addition, some indirect effects of UV-B are also
observed which alters the rate of photosynthesis, such as, stomatal closure, changes in leaf
thickness and anatomy, decrease in individual leaf area and total canopy leaf area. Stomatal
closure leads to reduction of evapotranspirational loss of water and water use efficiency gets
increased, which ultimately leads to increased plant growth. According to Van Rensen et al.
(2007) damage caused by UV-B radiation occurs first on the acceptor side of photosystem II
and only later on the donor side.
Due to elevated UV-B, changes in ultra-structure of leaves takes place, which modifies
the light attenuation by leaf and the total UV-B radiation in turn, affect photosynthesis. Leaf
reflects 3-6 per cent to 10-40 per cent UV-B radiation from pubescent or glaucous surface. An
increase in incident UV-B radiation would increase the amount transmitted if no additional
reflection occurs at leaf surface. Plant species differed in their anatomical responses to UV-B

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radiation, while increase in leaf thickness due to UV-B was common. The palisade cells from
UV-B irradiated leaves of species were wider. The increase in cell number would increase the
cell wall surface area, which blocks and prevents the harmful UV-B radiation from reaching
the abaxial photosynthetically active mesophyll. The increased palisade cell number would also
increase the amount of air cell wall interfaces, an important parameter that affects reflectance
and transmission of the incident radiation through the leaf surface. Other changes produced by
elevated UV-B include more trichomes on the abaxial leaf surface, a reduction in number and
diameter of xylem tubes, decreased stomatal frequency and distorted leaf area. These adverse
effects of UV-B on leaf anatomy would inhibit the uptake of CO2 and in turn more assimilate
production. UV-B exposure also reduces the CO2 fixation by decreasing the activity and
concentration of Rubisco. This decline in the activity of Rubisco is due to the decrease in
soluble protein.
Although, photosynthesis is directly related to the biomass accumulation in plants but
reduction in biomass is not necessarily related with the UV induced reduction in
photosynthesis. To cope up with prevailing climatic conditions, light and UV-B stress, plant
induces the synthesis of various secondary metabolites, which also alters the physiological
processes and might be a reason for reduction of biomass.
Biochemical responses against UV-B and defence mechanisms adapted by the plants
UV-B is well known for its deleterious effects and severe consequences on various
physiological and biochemical characteristics of economically important plants. UV-B
penetrates through leaves and is absorbed by chromophores associated with the photosynthetic
apparatus. Leaves absorb over 90 per cent of incident UV-B. Leaf surface reflectance in the
wavelength is generally below 10 per cent and there is negligible transmission of UV-B through
leaves. Cell components which absorb UV-B directly include nucleic acids, proteins, lipids and
quinones. Water soluble phenolic pigments such as flavonoids are also found in leaves, which
strongly absorb UV-B radiations and protect the plants. UV-B stress leads to the production of
reactive oxygen species. Rao et al. (1996) proposed that UV-B activates membrane localized
NADPH oxidase, which then leads to the generation of ROS. Plants comprised of several
strategies to acclimatize and metabolise ROS. These includes active defence systems using low
molecular weight antioxidants such as ascorbic acid, phenols, flavonoids, glutathione,
carotenoids, etc and high molecular weight enzymes such as superoxide dismutase (SOD),
ascorbate peroxidase (APX), peroxidase (POD), catalase (CAT), etc. Increased levels of UV-B
radiations are responsible for the increased reflectivity of the plants surface i.e. the leaves
becomes more shiny and glabrous because of the increased deposition of waxy material. It is a
common type of defense mechanism acquired by the plants to protect them from harmful UV-
B radiation. Excess UVB exposure also induces the bronzing and reddening of leaves, due to
more production of polyphenolic compounds like flavonoids.

Impact of increase temperature on plant

Annual crops: Projected air temperature increases throughout the remainder of the 21st century
suggests that grain yields will continue to decrease for the major crops because of the increase
temperature stress on all major grain crops. Beyond a certain point, higher air temperatures
adversely affect plant growth, pollination, and reproductive processes. However, as air
temperatures rise beyond the optimum, instead of falling at a rate commensurate with the
temperature increase, crop yield losses accelerate. For example, an analysis by Schlenker and
Roberts (2009) indicated yield growth for corn, soybean, and cotton would gradually increase

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with temperatures up to 29°C to 32°C and then sharply decrease with temperature increases
beyond this threshold. Increases of temperature may cause yield declines between
2.5 per cent and 10 per cent across a number of agronomic species throughout the 21st century.
Other evaluations of temperature on crop yield have produced varying outcomes. Lobell et al.
(2011) showed estimates of yield decline between 3.8 per cent and 5 per cent and Schlenker
and Roberts (2009) used a statistical approach to estimate wheat, corn, and cotton yield declines
of 36 per cent to 40 per cent under a low CO2 emissions scenario, and between 63 per cent to
70 per cent for high CO2 emission scenarios. These estimates of yield loss did not consider the
positive effects of rising atmospheric CO2 on crop growth, variation among crop genetics,
impact of biotic stresses on crop growth and yield, or the use of adaptive management
strategies, e.g., fertilizers, rotations, tillage or irrigation. These analyses assumed that air
temperature increased without regard to the potential negative effects of temperature extremes.
The current evaluations of the impact of changing temperature have focused on the effect of
average air temperature changes; however, increases in minimum air temperature may be more
significant in their effect on growth and phenology. Minimum air temperatures are more likely
to increase under climate change. While maximum temperatures are affected by local
conditions, especially soil water content and evaporative heat loss as soil water evaporates,
minimum air temperatures are affected by mesoscale changes in atmospheric water vapour
content. Hence, in areas where changing climate is expected to cause increased rainfall or
where irrigation is predominant, large increases of maximum temperatures are less likely to
occur than in regions prone to drought. Minimum air temperatures affect night time plant
respiration rates and can potentially reduce biomass accumulation and crop yield. Welch et. al.
(2010) found higher minimum temperatures reduced grain yield in rice, while higher maximum
temperature raised yields; because the maximum temperature seldom reached the critical
optimum temperature for rice. However, under the scenario of future temperature increase, they
found maximum temperatures could decrease yields if they are near the upper threshold limit.
Similar responses have been found in annual specialty crops in which temperature is the major
environmental factor affecting production with specific stresses, such as periods of hot days,
over all growing season climate, minimum and maximum daily temperatures, and timing of
stress in relationship to developmental stages having the greatest effect. When plants are
subjected to mild heat stress (1 °C to 4 °C above optimal growth temperature), there was
moderately reduced yield. In these plants, there was an increased sensitivity heat stress 7 to 15
days before anthesis, coincident with pollen development. Subjecting plants to a more intense
heat stress (generally greater than 4 °C above optimum) resulted in severe yield loss extending
to complete crop failure. Tomatoes under heat stress fail to produce viable pollen while their
leaves remain active. The nonviable pollen does not pollinate flowers causing failure in fruit
set. If the same stressed plants are cooled to normal temperatures for 10 days before pollination,
and then returned to high heat, they are able to develop fruit. There are some heat tolerant
tomatoes which perform better than others related to their ability to successful pollinate even
under adverse conditions.
Perennial crops: Perennial crops have a more complex relationship to temperature than annual
crops. Many perennial crops have a chilling requirement in which plants must be exposed to a
number of hours below some threshold temperature before flowering can occur. For example,
chilling hours for apple (Malus domestica Borkh.) range from 400 to 2900 h (5 to 7 °C base
temperature) while cherry trees (Prunus avium) require 900 to1500 h with the same base
temperature. Grapes (Vitis vinifera L.) have a lower chilling threshold that other perennial

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plants with some varieties being as low as 90 h. Increasing winter temperatures may prevent
chilling hours from being obtained and projections of warmer winters by mid-21st century,
plants requiring more than 800 h may not be exposed to sufficient cooling except in very small
areas. Climate change will impact the chilling requirements for fruits and nut trees. Hatfield et.
al. (2014) showed that under a warming climate, adequate chilling hours for perennial crops
for fruit development may not be met. Innovative adaptation strategies will be required to
overcome this effect because of the long-time requirements for genetic selection and fruit
production once perennial crops are established. Perennial plants are also susceptible to
exposure to increasing temperatures similar to annual plants. These responses and the
magnitude of the effects are dependent upon individual species. Exposure to high temperatures,
>22 °C, for apples during reproduction increases th fruit size and soluble solids but decreases
firmness as a quality parameter. In cherries, increasing the temperature 3 °C above the 15 °C
optimum mean temperature decreases fruit set. Optimum temperature range in citrus (Citrus
sinensis L. Osbeck) is 22 to 27 °C and temperatures greater than 30 °C increased fruit drop.
During fruit development when the temperatures exceed the optimum range of 13 to 27 °C with
temperatures over 33 °C there is a reduction in Brix (sugar content), acid content, and fruit size
in citrus. Temperature stresses on annual and perennial crops have an impact on all phases of
plant growth and development. Exposure of plants to extreme temperatures will limit the ability
of the plant to produce fruit due to disruption of the pollination process. The magnitude of this
impact varies among species; however, there is a consistent negative impact on plants. One
aspect of high temperature extremes often over looked is the effect of extreme events on the
atmospheric water vapour demand. The saturation vapour pressure (e*) shows exponential
increase with increase in air temperature An increasing water vapour demand will cause more
water to be transpired by the leaf until the water supply becomes limited and the stomatal
conductance will decrease leading to a higher leaf temperatures and a reduction in
photosynthesis. If the plant is exposed to extreme temperatures, water stress could occur
quickly because the plant lacks sufficient capacity to extract water from the soil profile to meet
the increased atmospheric demand. The effects of temperature extremes on the plant could be
from the combined effect of the warm air temperatures and the increasing atmospheric demand.
The effects of extreme temperature from either acute or chronic exposure can have large
impacts on plant growth and development.

Climate change mitigation measures in India

Emissions and energy overview: India is the world’s fourth largest economy and fifth largest
greenhouse gas (GHG) emitter, accounting for about 5 per cent of global emissions.
India’s emissions increased 65 per cent between 1990 and 2005 and are projected to grow
another 70 per cent by 2020. By other measures, India’s emissions are low compared to those
of other major economies. India accounts for only 2 per cent of cumulative energy-related
emissions since 1850. On a per capita basis, India’s emissions are 70 per cent below the world
average and 93 per cent below those of the United States. India remains home to the world’s
largest number of poor people, with nearly 35 per cent living on less than a dollar a day. Its
economy is growing rapidly, however, with GDP rising about 8 per cent a year over the past
five years. As the economy has grown, emissions intensity (GHGs per unit of GDP) has
declined significantly. India’s GHG intensity is currently 20 per cent lower than the world
average (and 15% and 40% lower than the United States’ and China’s, respectively). Factors

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contributing to the decline in energy intensity include improved energy efficiency, increased
use of renewable and nuclear power, expanded public transport, and energy pricing reform.
With rapid economic growth, rising income, and greater availability of goods and services,
energy demand rose 68 per cent between 1990 and 2005, about 3.5 per cent annually. The
government projects energy demand growth of 5.2 per cent a year for the next 25 years, driven
by annual GDP growth rates of 8-10 per cent. Coal accounts for 39 per cent of total primary
energy demand, followed by biomass and waste (29%), oil (25%) and natural gas (5%). The
high proportion of biomass and waste reflects the fact that some 500 million people have no
access to electricity or other modern energy services. Coal is projected to remain the primary
energy source, with demand growing nearly three-fold by 2030.

International participation: India is a party to both the UN Framework Convention on

Climate Change and the Kyoto Protocol. As a non-Annex I (developing) country, India has no
binding emission limits under the Protocol. However, India is an active participant in the Clean
Development Mechanism (CDM) established by the Protocol. (The CDM grants marketable
emission credits for verified reductions in developing countries. Developed countries buying
these credits can apply them toward their Kyoto targets.) India has more than 345 registered
CDM projects, more than any other country, and about a third of all projects globally. (In terms
of the overall volume of CDM reductions, China ranks first with 51% followed by India at
14%.). The largest project categories are biomass and wind power. Most projects in India are
undertaken on a unilateral basis—developed independently by local stakeholders without the
direct involvement of Annex I countries.

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Policies contributing to climate mitigation
As in many other countries, India has a number of policies that, while not driven by
climate concerns, contribute to climate mitigation by reducing or avoiding GHG emissions.
(Specific estimates of the emission impacts of the policies described below are in most cases
not available. However, a recent analysis by The Energy and Resources Institute (TERI)
concluded that in the absence of a number of energy policies that are currently being
implemented, CO2 emissions would be nearly 20% higher compared to business as usual
scenarios in both 2021 and 2031). Many of these policies are contained in the Five Year Plans
developed by the Planning Commission to guide economic policy in India (the 11th Five Year
Plan covers 2007-2012). Other policies are found in the Integrated Energy Policy approved by
the Planning Commission in 2006 with the broad objective of meeting energy demand “at the
least cost in a technically efficient, economically viable and environmentally sustainable
manner.” In June 2008, Prime Minister Singh released India’s first National Action Plan on
Climate Change outlining existing and future policies and programs addressing climate
mitigation and adaptation. The plan identifies eight core “national missions” running through
2017 and directs ministries to submit detailed implementation plans to the Prime Minister’s
Council on Climate Change by December 2008.
Energy
Renewable Energy: Currently, modern renewable energy constitutes 4 per cent of the total
installed capacity of the power generating sector. Between 2002 and 2007, 6800 megawatts
(MW) of renewable power capacity was added, about 3000 MW more than the 10th Five Year
Plan target. The 11th Five Year Plan sets a target of increasing the installed capacity to 23,500
MW by 2012, or more than 10 per cent of total installed capacity, with wind comprising 72 per
cent and biomass and hydro power about 14 per cent each. The Electricity Act (2003)
encourages the development of renewable energy by mandating that State Electricity
Regulatory Commissions (SERCs) allow connectivity and sale of electricity to any interested
person and permit off-grid systems for rural areas. The National Tariff Policy (2006) stipulates
that SERCs must purchase a minimum percentage of power from renewable sources, with the
specific shares to be determined by each SERC individually. The states of Himachal Pradesh
and Tamil Nadu have the highest quotas—20 per cent by 2010 and 10 per cent by 2009,
respectively. Under the Rural Electrification Policy (2006) electrification of all villages must
be completed by 2012. Of the 80,000 villages that have no access to electricity, 18,000 villages
are in remote areas that must be electrified through use of renewable energy. Currently, about
3000 villages have been electrified, primarily through solar systems.
Wind Power: Wind power comprises over 65 per cent of renewable capacity, ranking India
fourth in terms of wind power generation worldwide. The Ministry of New and Renewable
Energy estimates the overall potential for wind power at 45,000 MW, with only about 6270
MW currently developed. In recent years, the policy framework has been strengthened to
reduce upfront costs to investors. Long-term low-interest loans are being provided by the Indian
Renewable Energy Development Agency. Cumulative loan approvals amounted to $1.9 billion
at the end of 2006. The central government allows 80 per cent accelerated depreciation for the
first year; concessions on import duties, sales tax and excise duties; and a 10- year income tax
exemption for profits from wind generation. Subsidies also are provided for demonstration
projects in states where commercial activity has not begun.

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Solar Power: Solar thermal projects receive financial assistance in the form of capital
subsidies, sales incentives, and reimbursement of fees. To encourage foreign investment in solar
photovoltaic technology, the government allows an automatic approval procedure for up to 74
per cent of foreign direct investment in joint venture projects. Up to 100 per cent foreign direct
investment is permitted if approved by the Foreign Investment Promotion Board. Various
subsidies and loans are also available for manufacturers and users of solar power. Raw materials
and photovoltaic components are exempt from excise duties and benefit from concessional
import duties. In New Delhi, the use of solar water heating systems in certain categories of
buildings has been made mandatory. In 2006, a rebate scheme was introduced in the domestic
sector to encourage the use of these systems. The government recently introduced a
demonstration program to support large grid interactive solar projects. The program sets a feed-
in tariff of 12 rupees (about 25 cents) per kilowatt-hour (kWh) for solar photovoltaic power and
Rs.10/kWh (~22c/kWh) for solar thermal power generation through 2009 for qualifying
projects.
Other Renewables: Biomass projects for power generation receive fiscal incentives including
subsidies, income tax holidays, excise duty and sales tax exemptions, and accelerated
depreciation. Currently, the CDM also attracts developers to build biomass projects.
Hydropower contributes 33,642 MW (or 26%) of electricity generated in India. The 11th Five
Year Plan calls for an additional capacity of 15,585 MW by 2012 and the Accelerated Hydro
Development Plan targets 50,000 MW of new capacity by 2025-26. Small hydropower projects
(up to 25 MW) are eligible for incentives such as concessional customs duties and income tax
exemptions for 10 years.
Coal: Currently, coal accounts for 55 per cent of electricity generation. According to the new
national climate action plan, about 7 per cent of the installed coal capacity is in inefficient plants
that will be retired by 2012, and an additional 10,000 MW will be retired or reconditioned by
2017. Three R&D plants based on Integrated Gasification Combined Cycle technology have
been established, and the government is encouraging the adoption of supercritical coal
combustion technologies. The 10th Five Year Plan calls for research and development of
advanced combustion technologies for the Indian power sector. The very high ash content of
Indian coal reduces the efficiency of coal-fired power generation, increasing the amount of coal
transported to power plants, and resulting in excess emissions from both transportation and
combustion. Since 2001, the use of washed coal has been mandated at all power plants more
than 1000 kilometers from the mining source, or in urban, sensitive and critically polluted areas.
The 10th Five Year Plan projects Coal Bed Methane (CBM) providing up to 19,260 MW of
power generation. The CBM Policy 1997 incentivizes investors to develop CBM commercially
by providing liberal fiscal terms.
Nuclear Power: Nuclear power presently accounts for 3 per cent of total power generation.
The Integrated Energy Policy sets a goal of increasing installed nuclear capacity from about
3900 MW to 20 gigawatts (GW), a five-fold increase, by 2020. To meet these targets, the 11th
Five Year Plan targets an additional 3160 MW in capacity and the 12th Five Year Plan will
further increase capacity by 11,000 MW, with the National Thermal Power Corporation
providing an additional 2000 MW. Energy Efficiency and Conservation
The Energy Conservation Act (2001) established a national Bureau of Energy Efficiency
(BEE) with the objective of improving energy efficiency in various sectors. BEE has developed
energy efficiency labels for refrigerators and other appliances, conducted mandatory energy

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audits of large energy-consuming industries, developed demand-side management programs,
and established benchmarks for industrial energy use. BEE is in the process of developing a
CDM project called the “Bachat Lamp Yojana,” which will replace all incandescent bulbs in
the residential sector with compact fluorescent lamps. The price differential will be recovered
by the sale of carbon credits. It is estimated that this will reduce 24 million tons of CO2 annually.
In 2007, the Energy Conservation Building Code was introduced, initially on a voluntary basis,
to establish energy performance requirements for commercial buildings with loads of 500 kW
and above. The National Tariff Policy (2006) implemented a higher tariff base for consumers
with a large demand (for example, in excess of 1 MW). States like Assam and Orissa have also
come up with state-level tariff policies to complement the central government efforts.
Transportation
Vehicles: The National Auto Fuel Policy (2003) mandated that all new four-wheeled vehicles
in eleven cities meet Bharat Stage III emission norms for conventional air pollutants, (similar
to Euro III emission norms), and comply with Euro IV standards by 2010. The largest urban
fleet of compressed natural gas (CNG) vehicles was introduced in New Delhi and Mumbai to
reduce pollution and increase energy security. In New Delhi alone, 106,000 vehicles, including
all buses, taxis and three-wheelers, were converted from gasoline or diesel to CNG. Vehicles in
cities like Vadodara, Surat, Ankleshwar and the state of Maharashtra also have been converted.
This combined effort resulted in the conversion of 375,000 vehicles by March 2007, with three-
wheelers forming the largest share (64%).
Mass Transit: The Delhi Metro subway system began construction in 1998 and will cover the
entire metropolitan region by 2021. Currently, only Phase I has been completed, with daily
ridership projected to reach 2.6 million by 2011. The Bangalore Metro Phase I is expected to
be operational by 2011 and projected to provide transportation for one million passengers per
day. The National Urban Transport Policy (2006) and the National Urban Renewal Mission
provide funding for development of mass transit strategies for cities. Currently bus rapid transit
systems are functional in the city of Indore and are being tested in Delhi.
Biofuels
The Ministry of Petroleum and Natural Gas is implementing a mandatory program for
the introduction of ethanol-blended gasoline (5% gasohol) nationwide by April 2008. However,
due to fluctuations in the supply of ethanol, the program is currently running behind schedule.
The Biodiesel Price Policy (2005) fixed the initial purchase price of biodiesel at Rs.25/liter
(~60c/liter). The government is formulating a national policy on biofuels to introduce financial
incentives, develop R&D for production and commercialization of ethanol and jatropha, and
establish a national biofuel development board.
Forestry
In 2005, the forest and tree cover in India was 24%.17 The 11th Five Year Plan proposes
an increase in the forest and tree cover of 1 per cent a year through 2012. In 2007, the Prime
Minister announced the Green India program to reforest 6 million hectares of degraded forest
lands.
Adaptation and mitigation measures
Two fundamental response options to the predicted climate change are mitigation and
adaptation to the climate change respectively.
Mitigation refers to controlling global climate change by reducing the emission of
greenhouse gases (GHGs) and enhancing their sinks, whereas adaptation mainly focuses on

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moderating impacts of climate change through a wide range of actions that are targeted at the
vulnerable system. Traditionally, mitigation has remained at the main focus than adaptation of
the climate change community, both from a scientific and from a policy perspective. Important
reasons for the focus on mitigation is that, mitigating climate change helps to reduce impacts
on all climate-sensitive systems, while the potential of adaptation measures is limited to a few
systems. Nonetheless, researchers have proposed comprehensive consideration of adaptation
options as a response measure to climate change along with mitigation mechanisms due to
following reasons:
a) Considering the amount of past GHG emissions and the inertia of the climate system,
climate change is inevitable, which can no longer be prevented even by the most ambitious
emission reductions,
b) Effect of emission reductions takes several decades to fully manifest on the other hand most
of the adaptation measures have more instant benefits,
c) Adaptations can be effectively implemented on a local or regional scale, while implementing
mitigation mechanisms require international cooperation, such that their efficacy is less
dependent on the actions of others.
Effective adaptation to climate change depends on the availability of two important
prerequisites:
a) Information on what to adapt to and how to adapt, and
b) Availability of resources to implement the adaptation measures.
Ground based information about the vulnerable systems and the stressors that it is
exposed to, and the transfer of resources to vulnerable societies in order to help them to prepare
to cope up with the inevitable impacts of climate change are thus necessary elements of a
comprehensive climate policy
Mitigation Strategies
1. Green Generation for Clean and Energy Secure India: more than 5 times increase in
Renewable Capacity from 35 GW (upto March 2015) to 175 GW by 2022.
2. National Solar Mission scaled up five-fold from 20 GW to 100 GW by 2022. Kochi Airport
is the World’s first airport to fully run on solar power.
3. Solar powered toll plazas envisaged for all toll collection booths across the country.
4. National Smart Grid Mission launched for efficient transmission and distribution network.
5. Green Energy Corridor projects being rolled out to ensure evacuation from renewable
energy plants.
6. Nationwide Campaign for Energy Conservation launched with the target to save 10 per cent
of current energy consumption by the year 2018-19.
7. Launched Smart Cities Mission to develop new generation cities by building a clean and
sustainable environment.
9. National Heritage City Development and Augmentation Yojana (HRIDAY) launched to
bring together urban planning, economic growth and heritage conservation in an inclusive
manner.
10. Atal Mission for Rejuvenation and Urban Transformation (AMRUT) is a new urban
renewal mission for 500 cities across India.
11. Launched one-of-its kind Swachh Bharat Mission (Clean India Mission) to make country
clean and litter free by 2019.
12. Zero Effect, Zero Defect (ZED) with Make in India campaign to enhance energy and
resource efficiency, pollution control, use of renewable energy, waste management etc.

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13. Formulated Green Highways (Plantation and Maintenance) Policy to develop 1,40,000 km
long “tree-line” along both sides of national highways.
14. Faster Adoption and Manufacturing of Hybrid & Electric Vehicles (FAME India) to
promote faster adoption and manufacturing of hybrid and electric vehicles.
15. Country's first passenger vehicle fuel-efficiency standards finalized.
16. Policies to increase production of energy efficient 3 phase locomotives and switchover to
100 per cent of these locos from 2016-17 onwards.
17. Policy directive issued to use 5 per cent bio-diesel in traction fuel in diesel locomotives.
18. National Air Quality Index launched with One Number, One Colour and One Description
to give the status of air pollution in a particular city.
Adaptation Strategies
1. Launched Soil Health Card Scheme. Additionally, 100 mobile soil-testing laboratories setup
across the country.
2. Paramparagat Krishi Vikas Yojana launched to promote organic farming practices.
3. The Pradhan Mantri Krishi Sinchayee Yojana launched to promote efficient irrigation
practices.
4. Neeranchal is a new programme to give additional impetus to watershed development in the
country.
5. Launched National Mission for Clean Ganga (Namami Gange) which seeks to rejuvenate
the river.
6. National Bureau of Water Use Efficiency (NBWUE) proposed for promotion, regulation
and control efficient use of water.
7. ‘Give It Up’ Campaign launched to encourage citizens to give up subsidy on cooking gas to
meet the needs of the truly needy citizens, thereby promote shift away from inefficient use
of biomass in rural areas.
Climate Finance Policies
1. Setting up of INR 3,500 million (USD 55.6 million) National Adaptation Fund.
2. Reduction in subsidies on fossil fuels including diesel, kerosene and domestic LPG.
3. Coal cess quadrupled from INR 50 to INR 200 per tonne to help finance clean energy
projects and Ganga rejuvenation.
4. Introduction of Tax Free Infrastructure Bonds for funding of renewable energy projects.

Mitigating climate change through transgenic crops

Agriculture contributes significantly to greenhouse gas (GHG) emissions. As indicated
by Philippot and Hallin (2011), plant breeding should therefore give priority to developing
cultivars that can be used in farming systems with reduced GHG emissions. In this regard,
transgenic crops have been contributing to lower GHG emissions through reducing fuel use,
due both to less pesticide applications and increasing the area grown under conservation
agriculture, which involves practices such as “no-till” or “reduced-till”. Brookes and Barfoot
(2012) estimated that farming with transgenic crops since 1996 has led to additional soil carbon
sequestered, equivalent to 133,639 million t of CO2. Likewise, transgenic poplar trees
overexpressing cytochrome P4502E1 – a key enzyme in the metabolism of a variety of
halogenated compounds – increased the rates of metabolism and removal of volatile
environmental pollutants such as hydrocarbons, including trichloroethylene, vinyl chloride,
carbon tetrachloride, benzene, and chloroform (Doty et al. 2007).

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 Nitrous oxide and dioxide are potent GHGs released by manure or nitrogen (N)
fertilizer, particularly in intensive cropping systems. Crops are bred for N-use efficiency (NUE)
because this trait is a key factor for reducing N fertilizer pollution, improving yields in N-
limited environments, and reducing fertilizer costs. There are various genetic engineering
activities for improving NUE in crops (Shrawat and Good 2008). The gene Alanine
aminotransferase from barley, which catalyzes a reversible transamination reaction in the
Nassimilation pathway, seems to be a promising candidate for accomplishing this plant
breeding target. Transgenic plants overexpressing this enzyme can increase N-uptake at early
stages of growth. This gene technology was licensed to a private biotech company, which was
founded with the aim of promoting sustainable agriculture (Daemrich et al. 2008). A patent
issued a few years ago gave this company the rights to use this gene technology in major cereals
– wheat, sorghum, rice, maize and barley – as well as in sugarcane. They have been testing the
technology with rice in China, and researching further with rice and wheat in India, and
assessing its value for maize and rice in sub-Saharan Africa through private-public
partnerships.
Keeping N in ammonium form will affect how N remains available for crop uptake and
will improve N-recovery, thus reducing losses of N to streams, groundwater and the
atmosphere. There are genes in tropical grasses such as Brachiaria humidicola and in the wheat
wild relative Leymus racemosus that inhibit or reduce soil nitrification by releasing inhibitory
compounds from roots and suppressing Nitrosomonas bacteria (Subbarao et al. 2007). Their
value for genetic engineering crops for reducing nitrification needs to be further investigated.
Almost one-fifth of global methane emissions are from enteric fermentation in ruminant
animals. Apart from various rumen manipulation and emission control strategies, genetic
engineering is a promising tool to reduce these emissions. The amount of methane produced
varies substantially across individual animals of the same ruminant species. Efforts are ongoing
to develop low methane-emitting ruminants without impacting reproductive capacity and wool
and meat quality. A recent study to understand why some sheep produce less methane than
others, by Rubin et al. (2014), deployed high-throughput DNA sequencing and specialized
analysis techniques to explore the contents of the rumens of sheep. The study showed that the
microbiota present in sheep rumen was solely responsible for the differences among low and
high methane-emitting sheep. It was further observed that the expression levels of genes
involved in methane production varied more substantially across sheep, suggesting differential
gene regulation. There is an exciting prospect that low-methane traits can be slowly introduced
into sheep. Re-engineering cereal photosynthesis
Photosynthesis involves the use of the sun’s energy to obtain sugar and oxygen after
binding CO2 and water. There are two types of photosynthesis in the major crop species: C3
and C4. In C3 photosynthesis CO2 is first incorporated into a 3–carbon compound and the
photosynthesis enzyme Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is
involved in CO2 uptake. In C4 photosynthesis CO2 is first incorporated into a 4–carbon
compound and phosphoenolpyruvate carboxylase (PEP) is the enzyme involved in the uptake
of CO2. C4 photosynthesis occurs in inner cells and requires the special Kranz anatomy, while
C3 photosynthesis takes place throughout the leaf. Photosynthetic efficiency in C4 species
(maize, sorghum, sugar cane) can exceed that of C3 species (rice, wheat) by up to 50 per cent
at temperatures above 21 to 23°C. This is due to photorespiration suppression in the former. C3
plants are well adapted to environments with cool temperatures. Genetic engineering C4
photosynthesis into C3 plants has been advocated to improve photosynthetic efficiency

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(Hibberd et al. 2008), which should translate into increasing biomass and grain yields per unit
of water transpired. Ghannoum (2009) warns, however, that C4 photosynthesis is highly
sensitive to water stress (more so than C3 photosynthesis). Another genetic engineering
approach considers introducing components of a high efficient CO2-concentrating mechanism
from blue-green algae (cyanobacteria) into chloroplasts of C3 plants. Mathematical modelling
suggests that photosynthesis may improve up to 28 per cent by introducing single-gene
cyanobacterial bicarbonate transporters BicA and SbtA into C3 chloroplasts (Price et al. 2013).
There have been many attempts at introducing transgenes into nuclear and plastid genomes to
increase photosynthetic efficiency (Maurino and Weber 2013). This very ambitious genetic
engineering undertaking may prove to be very difficult – introducing C4 photosynthetic
enzymes and changes in leaf anatomy and biochemistry into C3 species will depend on several
hundred genes. Denton et al. (2013) indicate that the genetic basis of C4 photosynthesis remains
mostly unknown, but there are some advances in understanding it through comparative genetic
analysis of C3 and C4 species facilitated by the completion of their genome sequencing.
Manipulating Rubisco has been regarded as a primary target for enhancing
photosynthesis, thus improving both crop yield and input efficiency (Parry et al. 2013).
Mathematical modelling suggests that genetic engineering plants expressing different types of
Rubisco in sunlit and shade leaves may maximize C gains at current and elevated CO2 levels
(Zhu et al. 2004). Hanson et al. (2013) give an overview on manipulating Rubisco properties
through plastid genetic engineering and how plastid operons could be changed for expressing
various genes involved in pathways or controlling enzymes enhancing photosynthetic rates or
reducing photorespiration.
Beyond climate change adaptation and mitigation: the transgenic pipeline
In spite of the positive impacts of farming transgenic crops, there are few transgenic
traits and cultivars used commercially (Lemaux 2006). Herbicide tolerance, host plant
resistance to insects and viruses, crop nutrient composition, and extended shelf life were the
main traits of the first generation of approved transgenic cultivars. These included transgenic
cultivars of alfalfa (lucerne), canola, cotton, eggplant, maize (including sweet corn), papaya,
potato, rice, squash, soybean, sugar beet, and tomato. The newest release includes enhanced
maize adaptation to drought-prone environments. A very recent e-conference convened by the
United Nations Food and Agriculture Organization (FAO) highlighted some of the traits and
crops in the genetic engineering pipeline ensuing from both private and public endeavours
targeting the developing world (Ruane 2012). Traits are related to host plant resistance to
pathogens (bacteria, fungi, nematodes, viruses) and insects, tolerance to herbicides, enhanced
food and feed quality (β-carotene, fatty acid profiles, high lysine, low phytate content),
enhanced adaptation to stressful environments (due to drought, heat and salinity), and improved
input efficiency (nitrogen, water). Crops covered include banana, bean, cabbage, canola,
cassava, chickpea, cotton, cowpea, eggplant, groundnut (peanut), maize, potato, rice,
pigeonpea, sorghum, soybean, sugarcane, and wheat. Tammisola (2010) indicated that the
global biofuel demand may pave the way for further use of genetic engineering for improving
bio-energy crops and tapping the crop wild relative gene reservoir.
A

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