Class #24

INDIAN CLIMATE
In India, the monsoonal climate determines all social, cultural, and economic activities. The Indian
climate is considered to be a tropical monsoon climate as monsoon plays a significant role in affecting
people’s lives.

FEATURES OF THE MONSOON CLIMATE:

1. Tropical type of climate:
o Majorly experienced in tropical areas.
o Also found in lower temperate mid-latitudes. Eg: Eastern China
2. Seasonal reversal of winds:
o Refers to the change of direction of the wind from onshore (winds blowing from sea to land)
during summer rainy months to offshore (winds blowing from land to sea) during the winter
dry months.
3. Trade wind modification:
o This seasonal reversal of wind during monsoon is a modification of trade winds.
4. Characterised by wet and dry seasons:
Alternate seasons of floods and droughts are found during the monsoon season.
o Heavy rainfall during onshore winds leads to floods
o Dry conditions during offshore winds lead to drought conditions.
5. Regions:
o Confined to South Asia, and Southeast Asia including the Philippines, Northern Australia and
Eastern Africa.
o Also seen in West Africa (Gulf of Guinea) which is referred to as pseudo monsoon (refers to
the monsoon where the seasonal reversal of winds does not surface out well).
6. Monsoons in Temperate regions: Also confined to eastern coasts of low mid-latitudes.

SALIENT FEATURES OF THE INDIAN CLIMATE:

1. The reversal of winds:
o Indian climate is characterized by the complete reversal of the wind system with the change
of seasons in a year.
o In winter, the wind blows across the Indian subcontinent from northeast to southwest
direction.
o During the summer season, it blows from southwest to northeast.
2. Formation of Alternatively High and Low-Pressure Areas over the Land:
o With intense heating of land in summers, thermally induced low-pressure cells are formed
over the northwestern part of India and high-pressure zones are created over the Arabian
Sea.
o In winters, a high-pressure zone is formed in the northwestern part of India while the low-
pressure zone is formed over the Oceans.
o The change in atmospheric pressure conditions results in change of seasons.
o These pressure differences guide the direction and intensity of wind flow.
3. Seasonal Variability in Rainfall:
o In India, over 80% of the annual rainfall occurs during the end of summer for 1 to 5 months
across the country. This seasonal variability helps in the cultivation of a number of crops
belonging to tropical, temperate as well as frigid areas.
4. The plurality of seasons:
o Indian climate is characterized by three main seasons, but broadly five a year (winter, spring,
summer, rainy, and autumn).
5. Unity of Indian Climate:
o Despite the seasonal variations, the Indian climate is tropical.

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o This is because the Himalayas and the associated mountain ranges prevent the cold
northerly winds of Central Asia from entering India.
o Thus, parts of India extending north of the Tropic of Cancer too experience a tropical climate.
o Himalayan ranges also restrict the movement of southwestern monsoonal winds beyond the
Himalayas, forcing the monsoon winds to cause rainfall over India.
6. Diversity of Indian Climate:
o Indian climate is characterized by regional differences and variations.
o In the summer the temperature occasionally touches 55°C in western Rajasthan, and it drops
down to as low as minus 45°C in winter around Leh.
o The differences are visible in terms of winds, temperature, rainfall, humidity, aridity, etc.
which are caused by differences in location, altitude, distance from the sea, distance from
mountains, and general relief conditions at different places.
7. Characterized by Natural Calamities:
o The changing weather conditions, especially rainfall variability have made the Indian climate
more prone to natural calamities like floods, droughts, famines, and even epidemics.

FACTORS DETERMINING INDIA’S CLIMATE:

1. Latitude:
o The Tropic of Cancer passes through the central part of India in an east-west direction -so, the
northern part of India lies in the sub-tropical and temperate zone and the southern part falls
in the tropical zone.
o The tropical zone being near the equator experiences consistent climatic conditions
throughout the year.
o The area farther from the equator experiences an extreme climate with a high daily and
annual range of temperature.
2. The Himalayan Mountains:
o The Himalayas act as an effective climatic divide between central Asia and the Indian
subcontinent obstructing cold winds from Arctic Circle.
3. Distribution of Land and Water:
o India is flanked by the Indian Ocean on three sides in the south and surrounded by a high and
continuous mountain wall in the north.
o The water heats up and cools down more slowly than the landmass – the differential heating
creates different air pressure zones in different seasons in and around the Indian
subcontinent.
4. Distances from the Sea:
o The coastal areas of India have an equable climate, because of the moderating influence of
the sea.
o The interior parts experience climate variations and extremes due to the absence of this
moderating influence.
5. Altitude:
o Temperature decreases with height - as air ascends it loses its temperature based on the
Normal Lapse Rate.
o So, the places situated at higher altitudes are cooler than places located at relatively lower
heights. Eg: Agra and Darjeeling are located on the same latitude, but the temperature of
January in Agra is 16°C whereas it is only 4°C in Darjeeling.
6. Relief:
o The physiography or relief of India affects the temperature, air pressure, direction and
speed of the wind, distribution of rainfall etc.
o The windward sides of Western Ghats and Assam receive high rainfall during June-September
whereas the southern plateau remains dry due to its leeward situation along the Western
Ghats.

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CLIMATIC REGIONS OF INDIA:

A climatic region is a homogenous climatic condition that is the result of a combination of factors. The
climatic classification includes two important elements: temperature and rainfall.
● India has a monsoon-type of climate.
● However, many regional variations can be observed because of a combination of numerous
elements in the weather, based on which India’s climate can be divided into a number of climatic
regions.
● Despite many climatic regions, Koppen’s classification of climatic regions of India is more suitable.
o His classification of climatic regions corresponds to the mean monthly temperature, mean
monthly rainfall, and mean annual rainfall of India.
o Koppen mostly based his classification on the temperature and the precipitation data.

Koppen recognized five major types of climate that correspond with five principal vegetation
groups:
A: Tropical humid climate without any cool season.
B: Dry climate
C: Mid-latitude rainy climate with mild winter climate
D: Mid-latitude rainy with severe winter climate
E: Polar climate

In addition to this, he further subdivided these major climatic regions based on the seasonal
distribution of rainfall or degree of dryness or cold. They are designated by a, c, f, h, m, g, s, and w.
Further S and W are designated to highlight Semi-arid or Steppe (S) and arid or desert (W). T is
designated to mention Tundra and F ice-cap.
Koppen’s classification of climate
The main classification of climatic regions of India included:

Tropical Savanna Climate (Aw):

● The temperature in the hottest month (May)- 40 degrees celsius.
● Temp remains above 18 degrees celsius in the cold months.
● The diurnal and annual ranges of temperature are high.
● Found in Peninsular India like Jharkhand, Odisha, Chhattisgarh, Andhra Pradesh, WestBengal, and
Maharashtra.
● The region receives rainfall during the southwest monsoon.

Tropical Monsoon Climate (Amw):

● Short and dry winter season.
● Vegetation- ever-green rain forests (as there is heavy rainfall during the southwest monsoon).
● Found in parts of Konkan Coast, Malabar Coast, and areas joining the western ghats, Tamil Nadu
plateau, and areas of Tripura and Mizoram.

Tropical Moist Climate (As):

● Mean annual temperature-18 degrees Celsius
● The region covers a Narrow zone along the Coromandal Coast.
● Average rainfall varies between 75 and 100 cm.

Semi-Arid Steppe Climate (BShw):

● Mean annual temperature- above 18 degrees celsius; experiences summer rainfall.
● Stretches over Eastern Rajasthan and rain shadow regions of Tamil Nadu, Karnataka, Gujarat,
and parts of southwest Haryana.

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Hot Desert Climate (BWhw):

● Mean annual rainfall is less than 25cm.
● Mean maximum summer temperature- 45 degrees.
● Winter temperatures drop to 0 degrees Celsius.
● Vegetation: Thorny bushes.
● Lies to the west of the Aravallis, Thar Desert.

Mesothermal Climate-Gangetic Plain Type (Cwg):

● The climate is marked by dry winter.
● Hot Summers
● Avg Temperature in cold months is 15 degrees Celsius.

Cold Humid Winter Climate (Dfc):

● The average summer temperature is -17 degrees Celsius
● Winter average temperature- 8 degrees Celsius.
● Cold humid winters and short summers.
● Mostly found in the hilly states of Sikkim and Arunachal Pradesh.

Polar Type (E):

● Found in higher reaches of the mountainous areas of Jammu and Kashmir, Himachal Pradesh,
and Uttarakhand.
● Warmest month Temp- less than 10 degrees.

Tundra Type (ET):

● Higher latitudes of Kashmir, Ladakh, Uttarakhand, and Himachal Pradesh.
● The warmest month Temperature lies between 0 to 10 degrees Celsius.

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INDIAN CLIMATIC CALENDAR

The Indian meteorological department has categorised the following four annual seasons:
(a) The Winter Season (January – February)
(b) The Summer season (March-May)
(c) The Rainy Season (Southwest Monsoon Season -(June – September)
(d) The Autumn season (October – December)

THE WINTER SEASON

● The winter season for the Indian subcontinent begins with the apparent southward movement of
the Sun. By the winter solstice in December(22nd December), the sun vertically shines over the
tropic of Capricorn. As a result, India being in the northern hemisphere experience the winter
season.
● In northern India, the cold weather season spans from mid-November to February. December and
January are the coldest months in north India. There is a gradual decrease in temperature upon
advancing from south to north in the winter season in India.
● The moderating impact of the sea and the closeness to the equator, subdue the winter season in
the Peninsular region of India. In the winter season, the northern part of India along with parts of
peninsular India is characterized by dry weather due to prevailing north-east trade winds from
land to sea. However, the coasts of Tamil Nadu experience rainfall as the same northeast trade
winds blow from sea to land.

Temperature in Winter Season:

● The 20°C isotherm runs roughly parallel to the Tropic of Cancer.
● To the south of this isotherm, the temperatures are above 20°C.

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o Here there is no distinctly defined

winter weather. Some parts of
Kerala and Tamil Nadu typically
experience temperatures near
30°C.
● To the north mean temperatures are
below 21°C and the winter weather is
distinct.
● The mean minimum temperature is
about 5°C over north-west India and
10°C over the Gangetic plains.
● Dras Valley in Kashmir is the coldest
place in India. The minimum
temperature recorded at Dras was –
45°C in 1908.

Pressure in the Winter Season:

● High air pressure prevails over large
parts of northwest India.
● Pressure is comparatively lower in
south India.
● The winds start blowing from the high-pressure area of the north-west to the low-pressure area
of the southeast.

Western Disturbances in Winter Season

The winter season in the northern plains is characterized by western disturbances which result in
rainfall in the plains and snowfall in the mountains.

What are western disturbances?

● Western disturbances are low-pressure systems (disturbances) that flow from west to east
(western winds) under the influence of the westerlies.
● Western disturbances are low pressures that are formed over the Mediterranean Sea that travels
over Iran, Iraq, Afghanistan, and Pakistan carrying a good amount of moisture in the winter season
in the northern hemisphere. Western disturbances influence large parts of northwest and north
India during the winter season.

The emergence of western disturbances:

● Western disturbances emerge over the Mediterranean Sea as extra-tropical cyclones or mid
latitude cyclones.
● A high-pressure condition is formed over Eastern Europe which leads to the intrusion of cold air
from Polar Regions into the relatively warmer air regions resulting in a pressure change.

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● This change in pressure creates a favorable condition for cyclogenesis in the upper layer of the
atmosphere which then promotes the formation of an eastward-moving extratropical depression
in the sea.
● These depressions travel across the Middle East, Iran, Afghanistan, and Pakistan and enter into
the Indian subcontinent. These moisture-laden depressions or disturbances finally hit the
Himalayas and fall over as precipitation in the form of rainfall and snowfall.

Benefits of western disturbances:

● Western disturbance brings winter rainfall in India: The western disturbances in the winter
season in the Indian subcontinent affect the weather conditions and helps in bringing occasional
rainfall.
● India gets close to 5-10% of its total annual rainfall from western disturbances.
● The North India depends upon snow and rain from western disturbances during the winter season
from November to March.

Western disturbance assists in agriculture: The winter precipitations play a great role in agriculture.
This rainfall is highly beneficial for the standing Rabi crops.
● Helps in rice and Jute cultivation in West Bengal.
● Helps in wheat cultivation in the Punjab region of India.
Weak western disturbances result in crop failure and drought-like situations across north India.

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Western disturbances are not associated with disasters as they are not high intensity weather
systems.

Tropical Cyclones in Winter Season:

● This is the season of the least tropical cyclone activity.
● The frequency of tropical cyclones decreases with the advancement of the season.
● This is due to low sea surface temperature and exit of ITCZ farthest south.
● The storms which are born in the Bay of Bengal strike Tamil Nadu and bring heavy rainfall.
● Some of them cross the southern peninsula over to the Arabian Sea.
● Some storms originate in the Arabian Sea and move towards either north or west.

Precipitation in Winter Season:

● The retreating winter monsoons pick up some moisture while crossing the Bay of Bengal and
cause winter rainfall in Tamil Nadu, south Andhra Pradesh, south-east Karnataka and south-east
Kerala (Usually in the first weeks of November).
● The highest seasonal rainfall of about 75 cm between October and December.
● Most of it occurs along the southeastern coast of Tamil Nadu and adjoining parts of Andhra
Pradesh, then gradually decreases.
● The western disturbances also cause little rainfall in northwest India.
● The amount of rainfall gradually decreases from the north and northwest to the east (it is the
opposite in the rainy season).
● The northeastern part of India also gets rainfall during the winter months.

SUMMER SEASON IN INDIA

● The summer season in
the northern
hemisphere is marked by
the apparent movement
of the sun towards
tropics of cancer. This
movement begins after
the march equinox(21st
March) and continues till
the summer solstice(21st
June) every year.
● There is intense heating
of the Indian
subcontinent and the
Tibetan plateau during
this period.
● The tropical areas lying
north of the equator are
exposed to higher solar
radiation, resulting in
intense heating of the
northern plains and the
adjacent highlands of
India. This intense
heating creates a low-
pressure trough that extends from the Punjab plains in the northwest to the Bengal delta in the
east.

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● This low-pressure zone draws winds from the adjoining areas, however, upon further
intensification, the pressure gradient also increases. This continues from March till May.
● During the month of March, the ITCZ is present predominantly around the equator and the sub-
tropical jet streams are present around 20-25 degrees north latitude.
● As the sun shifts northwards toward the tropic of cancer, there is intense heating of the Indian
subcontinent. This heating results in the formation of the low-pressure zone over the
subcontinent.
● This low-pressure zone doesn't immediately attract the monsoonal winds because of two reasons:
1. The presence of the subtropical jet streams blows to the south of the Himalayas.
2. The presence of a subtropical high-pressure belt over the northern plains.
● By the end of March and the beginning of April, we notice the northward movement of the
subtropical jetstreams(STJ) and the ITCZ.
● During April, we also notice the splitting up of the STJ into two branches, the northern branch and
the southern branch. The northern branch moves over the Himalayan mountain ranges and the
southern below the Himalayas.
● The movement of the ITCZ over the Indian subcontinent also results in occasional thunderstorms
in the regions where the ITCZ moves.

(1) Temperature in the Summer Season

● The southern parts of the country are warmer in March and April and in June, north India has
higher temperatures.
(a) In March, the highest temperatures occur in the southern parts (40-45°C).
(b) In April the highest temperature of about 45°C is recorded in the northern parts of Madhya
Pradesh.
(c) In May the highest temperature shifts to Rajasthan (temperatures as high as 48°C).
(d) In June the maximum temperature is in Punjab and Haryana.
● Highest temperatures recorded just before the onset of the southwest monsoons (late May).
● The diurnal range of temperature-very high.
● Maximum summer temperatures are comparatively lower in the coastal and southern peninsular
regions due to moderating effect of the sea.
● The temperatures along the west coast are comparatively lower than on the east coast due to the
prevailing westerly winds.
● There is a large contrast between land and sea temperatures.
● Northern and central parts of India experience heat waves in this season.

Heat Wave:
A heat wave is an abnormally high temperature experienced by a region. The temperature increase
of the order of 6° to 7°C above normal is termed as ‘moderate’ and 8°C and more as ‘severe’ heat
wave.
• Most of the heat waves develop over Rajasthan, Punjab and Haryana- location far away from
the sea from where they spread over Uttar Pradesh and Bihar.
• The strong north-westerly winds (caused due to strong divergence in north-west India) with a
long land journey over hot regions check the onward march of the sea breeze over the eastern
coastal belt and create heat wave conditions over Odisha and Andhra Pradesh.
• The heat waves strike by the end of April and their maximum occurrence is in May. They last
till the onset of the southwest monsoon.
• The normal duration of heat waves is 4 to 5 days. However, heat waves are rare over the
peninsula south of 13°N latitude due to maritime conditions prevailing there.

(2) Pressure in Summer Season:

● The atmospheric pressure is low all over the country due to high temperatures.

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● But strong dynamically induced divergence over northwest India prevents the onset of southwest
monsoons.

Winds in Summer Season: There is a change in the direction and speed of the winds from winter. The
winds are by and large light and variable.
1. Loo:
● Loo winds originate over the Iranian, Baloch and Thar deserts.
● In May and June, high temperature in northwest India builds a steep pressure gradient.
● Hot, dust-laden and strong wind (loo) blows.
● It starts blowing by 9.00 A.M., increases gradually and reaches maximum intensity in the
afternoon.
● It blows with an average speed of 30-40 km per hour and persists for days.
2. ANDHIS
● The strong dust storms resulting from the convective phenomena are locally known as andhis
(blinding storms). They move like a solid wall of dust and sand.
● The wind velocity often reaches 50-60 kmph and the visibility is reduced to a few metres.
● Common in Rajasthan, Haryana, Punjab, Jammu region, Delhi, Uttar Pradesh, Bihar and
Madhya Pradesh.
● They are short-lived.
● The showers which follow these storms bring down the temperature temporarily.

3. Frontal Thunderstorms:
● The strong convectional movements related to the westerly jet stream lead to thunderstorms
in the eastern and northeastern part of the country.
● They originate over the Chota Nagpur plateau and are carried eastwards by westerly winds.
● Seen in Assam, Arunachal Pradesh, Nagaland, Mizoram, Manipur, Tripura, Meghalaya, West
Bengal and the adjoining areas of Odisha and Jharkhand.

4. Norwesters and Thunderstorms

● In West Bengal and the adjoining areas of Jharkhand, Odisha and Assam, the direction of
squalls is mainly from the northwest, and they are called norwesters.
● They are often very violent with squall speeds of 60 to 80 km per hour.
● Hailstones sometimes accompany showers and occasionally attain the size of a golf ball.
● They cause heavy damage to standing crops, trees, buildings, and livestock and even lead to
loss of human lives.
● Sometimes, useful for tea, jute and rice cultivation. In Assam, these storms are known
as ‘Barodoli Chheerha’.
● The period of maximum occurrence of these storms is the month of Vaisakh (mid-March to
mid-April) and hence, they are locally known as Kalabaisakhis, the black storms or a mass of
dark clouds of Vaisakha.

5. Convectional Thunderstorms
● In the south, thunderstorms occur in Kerala (Mango Showers) and adjoining parts
of Karnataka (Blossom Showers) and Tamil Nadu, particularly during evenings and nights.
6. Western Disturbances:
● Their frequency and intensity gradually decrease with the advancement of summer.
● Approximately 2-3 western disturbances visit north-west India in March, April and May
respectively.
● They cause snowfall in higher reaches of the Himalayas.
7. Tropical Cyclones:
● Tropical cyclones originate in the Bay of Bengal and the Arabian Sea.

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● A few cyclones are formed in the Bay of Bengal in the month of March but they do not affect
mainland of India.
● Their frequency rises steeply in April and the number of cyclones originating in May is more
than double than those originating in April.
● About three-fourths of tropical cyclones are born in the Bay of Bengal and the rest originate
in the Arabian Sea.
● Most of the depressions in April originate to the south of 10°N while those originating in May
are born to the north of this latitude.
● Most of the storms of this season initially move west or north-west but later they recurve
northeast and strike Bangladesh and the Arakan Coast of Myanmar.
● Very few hit Indian coast while some dissipate over the sea itself.
● The whole of the east coast of India, the coastal areas of Bangladesh and Arakan Coast of
Myanmar are liable to be hit by tropical storms in May.
● Many of them are quite severe and cause heavy damage to life and property.
● In the Arabian Sea, major storms are formed in May between 7° and 12° N latitudes.
● Most of them move away from the Indian coast in a north-westerly direction and dissipate in
the sea.
● Few originate close to the Indian coast. They move towards the northeast and hit somewhere
along the west coast of India.

Precipitation:
● The summer season is not totally rainless (only one per cent of the annual rainfall).
● In the northeastern parts of the country, dust storms bring little rainfall.
● The precipitation in Kashmir is mainly in the form of snow caused by western disturbances.
● The norwesters bring some rainfall in Assam, West Bengal and Odisha. The intensity of rainfall is
high.
● The rainfall brought by the norwesters is known as the spring storm showers.
● This small amount of rainfall is very useful for the cultivation of tea, jute and rice and is known
as tea showers in Assam.
● Coastal areas of Kerala and Karnataka receive rainfall from thunderstorms.

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