THE CLIMATE OF INDIA

 India has tropical monsoon type of climate. It is greatly moderately cold in most of the regions while the
influenced by the presence of the Himalayas in the summers are extremely hot. Himalayan regions
north as they block the cold air masses from Central experience brutal winters while the summers are
Asia. It is because of them only that the monsoons have moderate.
a watershed in India. Variations in Precipitation
 The Tropic  While snowfall occurs in the Himalayas, it only rains
of Cancer over the rest of the country.
divides  Similarly, while Cherrapunji and Mawsynram in the
India into Khasi Hills of Meghalaya receive rainfall over 1,000 cm
two in a year, Jaisalmer in Rajasthan rarely gets average 21
almost cm of rainfall during the same period.
equal  Most parts of the country get rainfall during June-
climatic September, but in the coastal areas of Tamil Nadu, it
zones, rains in the beginning of the winter season. Places like
namely, Goa, Hyderabad and Patna receive S.W. monsoon rains
the by the first quarter of June while the rains are awaited
northern till early July at places in N.W. India.
zone and  FACTORS DETERMINING THE CLIMATE OF INDIA
the southern zone. The warm temperate or the A. FACTORS RELATED TO LOCATION AND RELIEF
subtropical climate of the northern zone gives it cold 1. Presence of Himalayas
winter seasons and the hot summer seasons. The  This is the most important factor that influences Indian
southern tropical climatic zone is warmer than the Climate (already discussed).
north and does not have a clear-cut winter season.  If the Himalayas were not present, the monsoon winds
REGIONAL VARIATIONS IN CLIMATE would simply move into China and most of the north
 There are great regional differences and variations India would have been a desert.
experienced in India with respect to temperature, 2. Latitude
rainfall etc.  The Tropic of Cancer passes through the central part of
Variations in Temperature India in the east-west direction. Thus, the northern part
 Diurnal and annual temperature ranges are substantial. lies in the Sub-Tropical and Temperate Zone and the
Highest diurnal temperature ranges occur in the Thar part lying south of the Tropic of Cancer falls in the
Desert and the highest annual temperature ranges are Tropical Zone.
recorded in the Himalayan regions.  The Tropical Zone being nearer to the equator
 Both diurnal and mean annual temperature ranges are experiences high temperatures throughout the year
least in coastal regions. with small daily and annual range. Areas north of the
 In December, the temperature may dip to -40°C at Tropic of Cancer being away from the equator,
some places in Ladakh, while in many coastal regions experience extreme climate with high daily and annual
average temperature is 20-25°C. Winters are range of temperature.

https://strgk.on-app.in/app/oc/466231/strgk?utm_source%3Dwhatsapp%26
 The Indian Climate

3. • Distribution of Land and Water  Upper air circulation caused by factors controlling
 India is flanked by water bodies on three sides in the global weather and the inflow of different air
the south and girdled by a high and continuous masses and jet streams affects the climate of
mountain-wall in the north. India.
 As compared to the landmass, water heats up or  The inflow of western cyclones generally known
cools down slowly. This differential heating of land as disturbances during the winter season and
and sea creates different air pressure zones in tropical depressions during the S.W. monsoon
different seasons in and around the Indian period into India are also important factors.
subcontinent. The difference in air pressure causes  The northern zone does not have the mid-day sun
a reversal in the direction of monsoon winds. vertically overhead during any part of the year;
4. Distance from the Sea the southern zone has the mid-day sun almost
 With a long coastline, large coastal areas have an vertically overhead at least twice every year.
equable climate. Areas in the interior of India are  THE INDIAN MONSOON
far away from the moderating influence of the sea.  The most dominating factor of the Indian climate is
Such areas have extremes of climate. That iswhy the 'monsoon winds'. The term 'monsoon' has
the people of Mumbai and the Konkan coast have been derived from the Arabic word 'mausim'
hardly anyidea of extremes of temperature and meaning 'season'.
the seasonal rhythm ofweather.
 On the other hand, the seasonal contrasts in  Monsoons are seasonal winds which reverse their
weather at places in the interior of the country
such as Delhi, Kanpur and Amritsar affect the
entire sphere of life.
5. Altitude
 Temperature decreases with height. Due to thin
air, places in the mountains are cooler than places
on the plains. For example, Agraand Darjeeling
are located on the same latitude, but the January
temperature in Agra is 16°C, whereas it is only 4°C
in Darjeeling.
direction with the change of season. It is a double
6. Relief
system of seasonal winds -they flow from sea to
 The physiography or relief of India also affects the
land during the summer and from land to sea
temperature, air pressure, direction and speed of
during winter. Broadly speaking, monsoon winds
the wind and the amount and distribution of
are land and sea breeze on a large scale.
rainfall.
 Monsoons are peculiar to Indian Subcontinent,
 The windward sides of Western Ghats and Assam
South East Asia, parts of Central Western Africa
receive high rainfall during June-September,
etc., but are more pronounced in India.
whereas the southern plateau remains dry due to
 India receives S.W. monsoon winds in summers
its leeward situation along the Western Ghats.
and N.E. monsoon winds in winters.
S.W. monsoons are formed due to intense low
B. FACTORS RELATED TO AIR PRESSURE AND WIND pressure system formed over the Tibetan
plateau, migration of ITCZ to the north of
 Distribution of air pressure and winds on the equator and permanent high pressure cell in the
surface of the earth are also important factors. South Indian Ocean (east to N.E. of Madagascar)
in summer.

https://strgk.on-app.in/app/oc/466231/strgk?utm_source%3Dwhatsapp%26

Prepared by ARGHYA SIR 2

 The Indian Climate

 N.E. monsoons are associated with high pressure

cells over Tibetan and Siberian plateaus,
weakening of high pressure cell in the Southern
Indian Ocean and migration of ITCZ to the south of
equator.
 S.W. monsoons bring intense rainfall to most of
the regions in India and N.E. monsoons bring
rainfall mainly to Coromandel Coast (S.E. coast).
Note  In the summer season, the sun shines vertically
 Hippalus, a Greek navigator, is credited with over the Tropic of Cancer and the ITCZ shifts
discovering the monsoon wind in 45-47 CE. northwards. The S.E. trade winds of the southern
He is credited with discovering the direct
hemisphere cross the equator and start blowing in
route from the Red Sea to India through the
Indian Ocean. However, Pliny the Elder, a S.W. to N.E. direction under the influence of
Roman author, naturalist and philosopher, Coriolis force.
said that Hippalus discovered not the route  These displaced trade winds are called S.W.
but the monsoon wind which is also called monsoons when they blow over Indian sub-
Hippalus - the S.W. monsoon wind. continent.
MECHANISM OF MONSOON
 The front where the S.W. monsoons meet the N.E.
 Origin of monsoons is not fully understood. Several trade winds is known as the Monsoon Front (ITCZ).
theories have been given to explain the Rainfall occurs along this front.
mechanism of monsoons.
 In the month of July, the ITCZ shifts to 20°-25° N
 The first scientific study of the monsoon winds was
latitude and is located in the Indo-Gangetic Plain
done by Arab traders. They used the sea route to and the S.W. monsoons blow from the Arabian Sea
carry out trade with India and monsoon patterns
and the Bay of Bengal. The ITCZ in this position is
were of prime importance for them. In the tenth often called the Monsoon Trough (maximum
century, Al Masudi, an Arab explorer, gave an
rainfall).
account of the reversal of ocean currents and the
 The seasonal shift of the ITCZ has given the
monsoon winds over the north Indian Ocean.
concept of Northern Inter-Tropical Convergence
 In 1686, a British scientist Sir Edmund Halley Zone (NITCZ) in summer (July – rainy season) and
explained the monsoon as resulting from thermal
Southern Inter-Tropical Convergence Zone
contrasts between continents and oceans due to
(SITCZ)in winter (Jan dry season).
their differential heating.

ROLE OF ITCZ
 The S.E. trade winds in S.H. and the N.E. trade
winds in N.H. meet each other near the equator.
The meeting place of these winds is known as the
Inter-Tropical Convergence Zone (ITCZ). This is the
region of ascending air, maximum clouds and
heavy rainfall.
 The location of ITCZ shifts north and south of
equator with the change of season.

https://strgk.on-app.in/app/oc/466231/strgk?utm_source%3Dwhatsapp%26

Prepared by ARGHYA SIR 3

 The Indian Climate

JET STREAM THEORY 

Tibetan highlands act as a barrier in the path of
 It is the latest theory regarding the origin of the STJ. As a result, jet streams get bifurcated; one of
monsoons and has earned worldwide acceptance its branches blows to the north of the Tibetan
from the meteorologists. highlands, while the southern branch blows in an
 Sub-Tropical Jet stream (STJ) plays a significant role eastward direction, south of the Himalayas, later
in both hindering the monsoon winds as well as in recombining into a single stream over China. It is
quick onset of monsoons. Polar Jet has no believed that this southern branch of the jet
influence on Indian monsoons. stream exercises an important influence on the
 STJ in NH flows between 25° to 35° N in the upper weather in India.
troposphere at a height of about 12-14 km. IMPORTANT FEATURES OF INDIAN MONSOONS
 In winter, STJ flows along the southern slopes of  Sudden onset (sudden burst).
the Himalayas, but in summer, it shifts northwards,  Gradual progress.
rather dramatically, and flows along the northern  Gradual retreat.
edge of Himalayas in early June and in late  Seasonal reversal of winds.
summer (July-August) along the northern edge of  The complete reversal of the monsoon winds
the Tibetan Plateau. brings about a sudden change in the seasons, The
 This periodic movement of STJ is often the harsh summer season suddenly giving way to
indicator of the onset(STJ shifts to the north of monsoon or rainy season.
Himalayas in a matter of days) and subsequent  The S.W. monsoons from the Arabian Sea and the
withdrawal (STJ returns back to its position - south Bay of Bengal bring rainfall to the entire country.
of Himalayas) of the monsoon. Northward The N.E. winter monsoon does not cause much
movement of the subtropical jet is the first rainfall except along the Coromandel Coast (Tamil
indication of the onset of the monsoon over India. Nadu coast) after getting moisture from the Bay of
 There are major high velocity winds in the lower Bengal.
troposphere called Low-Level Jets (LLJs). In the Note
tropics, the most prominent of these are the  There are some essential factors required to cause
Somali Jet and the Tropical Easterly Jet-TEJ. monsoon rainfall. The most important is the unique
 The TEJ is a unique and dominant feature of NH geographical features that the subcontinent enjoys.
summer over southern Asia and northern Africa.  The presence of abundant water bodies around the
landmass is essential. For that we have the Arabian
The TEJ is found between 5and 20°N. It is fairly
Sea, the Indian Ocean and the Bay of Bengal. These
persistent in its direction and intensity from June help in accumulating moisture in the winds during the
through the beginning of October. hot season.
 TEJ comes into existence quickly after the ST] has  The presence of mountains or highlands like the
shifted to the north of the Himalayas (Early June), Western Ghats and the Himalayas, is also essential.
TEJ flows from east to west over peninsular India These ranges lie across the path of the S.W. monsoon
at 6-9 km and over the Northern African region. winds. When the winds hit these highlands, they are
forced to rise causing orographic precipitation
The formation of TEJ results in the reversal of
(precipitation which results when moist air is lifted
upper air circulation patterns (High pressure over elevated terrain).
switches to low pressure) and leads to the quick  Trees play a crucial role in the monsoon cycle. By
onset of monsoons. seeding clouds that encourage the rain to fall; by
 Role of Tibet: The Tibetan Plateau is an enormous trapping the moisture they help recharge the aquifers
block of highland acting as a formidable barrier. and hold groundwater in store for the common good.
Due to its protruded height, it receives 2 – 3oC Some water, rising with the cell sap, is returned to the
sky by transpiration through the leaves.
more insolation than the neighboring areas. The
 A well-stocked teak forest gives off the equivalent of
plateau affects the atmosphere in two ways: (a) as 1000 cm of precipitation. Great rainforests act on the
a mechanical barrier, and (b) as a high-level heat atmosphere like tropical seas; they supply it with water
source. vapour and help replenish the rains.

Prepared by ARGHYA SIR 4

 The Indian Climate

SEASONS IN INDIA
 India Meteorological Department (IMD) recognizes the
following four seasons: The Winter Season (January -
February)
 The Pre-monsoon Season or Summer Season (March -
May).
 The South-west Monsoon Season or Rainy Season (June
September)
 The Post Monsoon Season or Autumn Season (October
- December)

1. WINTER SEASON

Temperature Conditions
 On Dec 22, the sun shines vertically over the Tropic of
Capricorn in SH. So, India, which is located in NH,
experiences low temperatures.
 Clear sky, pleasant weather, low temperature, low
humidity, and high range of temperature, cool and  States like Punjab, Haryana and Rajasthan being far
slow N.E. trade winds. away from the moderating influence of sea experience
 The diurnal range of temperature, esp. in interior parts continental climate.
of the country, is very high.  The snowfall in the nearby Himalayan ranges creates
 The isotherm of 20oC runs roughly parallel to the Tropic cold wave situation; and
of Cancer. To the south of this isotherm, the  The cold winds coming from the Caspian Sea and
temperatures are above 20oC. Here, there is no Turkmenistan bring cold wave along with frost and fog
distinctly defined winter weather. Some parts of Kerala over the northwester pasts of India.
and Tamil Nadu typically experiences temperatures
near 30oC The Peninsular Region
 No well-defined cold weather season. Hardly any
 To the north, mean temperatures are below 21oC and seasonal change in the distribution pattern of the
the winter weather is distinct. Dras Valley in Kargil temperature in coastal areas because:
Dist., Ladakh, is the coldest place in India. The  Moderating influence of the sea, and
minimum temperature recorded at Dras was – 45oC in  Proximity to the equator.
1908. It is the Second Coldest Inhabited Place in the
world. It is often called The Gateway to Ladakh. Distribution of Air Pressure and Winds
 In winter months, the weather conditions over India are
The Northern Region generally influenced by the distribution of pressure in
 Begins in late-November in N. India. Lowest
the Central and Western Asia.
temperatures observed in Punjab and Rajasthan.
 A high-pressure centre in the region lying to the north of
 December and January are the coldest months in the
the Himalayas develops during winter. This centre of
northern plain.
high pressure gives rise to the flow of air from the north
 The night temperatures are, in fact quite low, towards the Indian subcontinent, south of the mountain
sometimes going below freezing point in Punjab and
range.
Rajasthan. Three main reasons for the excessive cold in
north India during this season:

https://strgk.on-app.in/app/oc/466231/strgk?utm_source%3Dwhatsapp%26

Prepared by ARGHYA SIR 5

 The Indian Climate

 These surface winds blowing out of the high-pressure rainfall in Tamil Nadu, south Andhra Pradesh, S.E.
centre over Central Asia reach India in the form of a dry Karnataka and S.E. Kerala (usually starts in October).
continental air mass.  The western disturbances also cause a little rainfall in
 These continental winds come in contact with trade N.W. India.
winds over N.W. India. The position of this contact  The amount of rainfall gradually decreases from the
zone is not, however, stable. Occasionally, it may shift north and north-west to east (it is opposite in rainy
its position as far east as the middle Ganga valley with season).
the result that the whole of the N.W. and N. India up to WESTERN DISTURBANCES
the middle Ganga valley comes under the influence of  The winter weather in India gets disturbed by
dry N.W. winds. shallow cyclonic depressions originating over the
east Mediterranean Sea. These temperate
cyclones travel eastwards across West Asia, Iran,
Afghanistan and Pakistan and enter the N.W. parts
of India with the help of Sub-Tropical Jet Stream.
 Since these extra-tropical cyclones reach India
from the West, they are usually referred to as the
Western Disturbances over the Indian region.

 Western Disturbances result in

 A cold spell in N.W. India, as these depressions is
followed by cold waves.
 Winter rainfall in Punjab, Haryana, Delhi and
western Uttar Pradesh, locally known as
'mahawat'.
 Highly beneficial for Rabi crops.
Distribution of Pressure and Winds in South India Snowfall in the higher altitudes of Kashmir and
 Here, the air pressure is slightly lower (due to higher Himachal Pradesh and sometimes hail too. This
temperatures). As a result, winds start blowing from snow sustains the flow of water in the Himalayan
northwestern high-pressure zone to the low air rivers during the summer months
pressure zone over the Indian Ocean in the south. The precipitation goes on decreasing from west to east
in the plains and from north to south in the
 The velocity of this wind is low due to low pressure mountains.
gradient. Free from the influence of topography, they  After the passage of the disturbance, widespread
are clearly north-easterly over the Bay of Bengal. These fog and cold waves lowering the minimum
winds cause rainfall along the Coromandel Coast since temperature by 5° to 10°C below normal are
they collect moisture from the Bay of Bengal. experienced. Fog lowers visibility and causes great
Precipitation in Winter Season inconvenience for transportation.
 The retreating winter monsoons pick up some moisture 2. SUMMER SEASON
while crossing the Bay of Bengal and cause winter  March to June; high temperature and low humidity are
the chief characteristics; sometimes referred to as Pre-
Monsoon Period.

https://strgk.on-app.in/app/oc/466231/strgk?utm_source%3Dwhatsapp%26

Prepared by ARGHYA SIR 6

 The Indian Climate

Temperature Conditions  Since the sun goes gradually towards the north (summer
 As the sun shifts northward towards the Tropic of Cancer solstice), ITCZ begins to move towards the north
after the Vernal Equinox, the whole India experiences an (eventually reaching up to 25o latitude in July).
increase in temperature.  In the months of May and June, the high temperature in
 The southern parts of the country are distinctly warmer N.W. India builds steep pressure gradient.
in March and April whereas in May and June, north India Loo and Andhis
has higher temperatures.  Under such conditions, hot dust-laden strong winds
 The diurnal range of temperature is also very high. It may known as 'loo' blow. Loo winds originate over Iranian,
be as high as 18°C in some ‘parts. Baloch and Thar deserts.
 North India: April, May and June are the months of  The strong dust storms resulting from the convective
summer in north India. In May, the heat belt moves phenomena are locally known as andhis. They move like
further north, and in the north-western part of India, a solid wall of dust and sand. The wind velocity often
temperatures around 48°C are not uncommon. reaches 50-60 kmph and the visibility is reduced to a few
 South India: The Peninsular situation of south India with metres.
moderating effect of the oceans keeps the temperatures  Such dust-storms are common in Rajasthan, Haryana,
lower than that prevailing in north India. So, Punjab, Jammu region, Delhi, Uttar Pradesh, Bihar and
temperatures remain between 26oC and 32oC Madhya Pradesh.
 Western Ghats: Due to altitude, the temperatures in the  They are short-lived. The squall and showers which follow
hills of Western Ghats remain below 25oC. these storms bring down the temperature sharply
 The temperature increases from the coast towards the temporarily (Squall-a sudden, violent gusty wind).
interior. Pre-Monsoonal Showers
 Occasionally, the moisture-laden winds are attracted
Heat Wave towards the periphery of the trough. A sudden contact
 Northern and central parts of India experience heat between dry & moist air masses gives rise to local storms
waves in this season. A heat wave is an abnormally high of great intensity. These local storms are associated with
temperature experienced by a region. Temperature violent winds, torrential rains and even hailstorms.
increase of the order of 5oC to 6oC above normal is  The thunderstorms which originate over Chhotanagpur
termed as 'moderate' and 7oC and more 'severe heat Plateau are carried eastwards by westerly winds. The
wave. areas with the highest incidence of thunderstorms are
 Most of the heat waves develop over Rajasthan, Punjab the NE States, West Bengal and the adjoining areas of
and Haryana (location far away from the sea). From here, Odisha and Jharkhand. These squalls are called
they spread over Uttar Pradesh and Bihar. Norwesters. Useful for tea, jute and rice cultivation.
 The strong north-westerly winds (caused due to strong  The period of maximum occurrence of these storms is the
divergence in N.W. India) with a long land journey over month of Vaishakh (mid-March to mid-April). These are
hot regions check the onward march of the sea breeze thus locally called Kal Baisakhi.
over eastern coastal belt and create heat wave conditions  In Assam, these storms are known as Bardoli Chheerha or
over Odisha and Andhra Pradesh. Bordoichila.
 The heat waves strike by the end of April and their  In the south, thunderstorms occur in Kerala and adjoining
maximum occurrence is in May. They last till the onset of parts of Karnataka and Tamil Nadu particularly in the
S.W. monsoon. evenings and nights. These pre-monsoonal showers are
Pressure in Summer Season called by various names:
 The atmospheric pressure is low all over the country due  Mango showers in Kerala and coastal areas of Karnataka
to high temperature. But strong dynamically induced as they help in the early ripening of mangoes.
divergence over N.W. India prevents the onset of S.W.  Cherry Blossoms in Karnataka and Kerala and nearby
monsoons. areas (good for coffee plantations).

https://strgk.on-app.in/app/oc/466231/strgk?utm_source%3Dwhatsapp%26

Prepared by ARGHYA SIR 7

 The Indian Climate

3. RAINY SEASON-S.W. MONSOON SEASON Entry & Progress of Monsoon into India
 Also known as hot-wet season.  Three-fourths of the total annual rainfall is received
 Sudden onset is the important feature of S.W. during this season.
Monsoons.  Normal date of the arrival of the monsoon is May 20 in
Temperature Conditions Andaman and Nicobar Islands.
 As the sun shifts northwards, the temperature rapidly  The advance of the monsoon is much faster in the Bay
increases, esp. in N. India. But with the onset of of Bengal than in the Arabian Sea.
monsoons, temperature falls drastically (5oC to 8oC  The normal date of onset of SW monsoon over Kerala,
between mid-June and mid-July) and humidity levels i.e. the first place of entry in mainland India, is June 1,
rise. At the same time, there is rise in temperature with a coefficient of variation of a week. The monsoons
whenever there is break in the monsoons. advance quickly accompanied with a lot of thunder,
 The diurnal range of temperature is small due to clouds lightning and heavy downpour. This sudden onset of
and rains. rain is termed as monsoon burst.
 The highest temperatures are experienced at places  Sometimes, monsoons are delayed or they come much
west of the Aravallis 38o to 40oC ) . This is due to lack of earlier than normal. Monsoon reaches the interior parts
clouds and hot continental air masses. The of the country by the first week of July. By mid-July, SW
temperatures are quite low over the Western Ghats due monsoon engulfs the entire subcontinent.
to heavy rainfall.  Monsoon winds beyond south Kerala progress in the
form of two branches:
A. THE ARABIAN SEA BRANCH
 The monsoon winds originating over the Arabian Sea
further split into three branches:
 First branch: It is obstructed by the Western Ghats,
causing very heavy rainfall (Orographic Rainfall) ranging
between 250 cm and 400 cm. These winds cause little
rainfall (30-50 cm) east of the Western Ghats. This is a
region of narrow belt of marked aridity and is known as
the rain-shadow area. But once it is passed, the air
starts rising again and the amount of rainfall increases
further east.
 Second branch: It strikes the north coast of Mumbai (by
June 10). Moving along the Narmada and Tapi river
valleys, these winds cause rainfall in extensive areas of
Distribution of Pressure and Winds
central India. The Chhotanagpur plateau gets 15 cm
 As a result of rapid increase in temperature in May over
rainfall from this part of the
the N.W. plains, the low-pressure conditions over there
 Third branch: It strikes the Saurashtra Peninsula and the
get further intensified.
Kutch. It then passes over W. Rajasthan and along the
 Because of the heating of the subcontinent, by the
Aravallis, causing only a scanty rainfall. In Punjab and
middle of July, the low-pressure belt near the surface
Haryana, it too joins the Bay of Bengal branch. These
(ITCZ) shifts northwards, roughly parallel to the
two branches, reinforced by each other, cause rains in
Himalayas between 20o N and 25o N. The ITCZ in this
the Western Himalayas.
position is sometimes called the monsoon trough.
 Though this branch passes through Rajasthan, it does
Roughly, this elongated low-pressure monsoon trough
not cause rainfall there. This is because:
extends over the Thar desert in the N.W. to Patna and
 The direction of Aravallis is parallel to these monsoon
Chhotanagpur plateau in the east-S.E.
winds.

https://strgk.on-app.in/app/oc/466231/strgk?utm_source%3Dwhatsapp%26

Prepared by ARGHYA SIR 8

 The Indian Climate

 The dry and hot winds from the Sindh region of proceeding to Myanmar, Thailand and
Pakistan lessen the Relative Humidity of these Malaysia.
monsoon winds and do not allow them to get  65% of the humidity brought by the monsoon
saturated. comes from the Arabian Sea whereas the
monsoon coming from the Bay of Bengal
 However, some orographic effect is evident on the
contributes only 35% to the humidity.
south-eastern edge of the Aravalli Range. Mt. Abu  The Tamil Nadu coast remains dry during this
gets about 160 cm rainfall while the surrounding season. It is because this coast lies in the rain-
plains have only 60 to 80 cm rainfall. shadow area of the Arabian Sea branch of the S.W.
B. BAY OF BENGAL BRANCH monsoon.
 It strikes the coast of Myanmar and parts of S.E.  In the Ganga Plains, the two branches merge into one.
Bangladesh. But the Arakan Yoma, along the coast of By the end of June, the monsoon is usually established
Myanmar, deflects a big portion of this branch towards over most parts of the country. By mid-July, the
the Indian subcontinent. monsoon extends into Kashmir and the remaining parts
 The monsoon, therefore, enters West Bengal and of the country. But, by the time it reaches Kashmir, it
Bangladesh from the south and S.E. instead of from the has shed most of its moisture.
S.W. direction. From here, this branch splits into two  The gradual reduction in the amount of rainfall towards
under the influence of the Himalayas and the thermal the west is evidenced by the decline from 160 cm at
low in N.W. India. Kolkata to 80 cm at Delhi and to desert conditions still
 One branch moves westward along the Ganga plains farther west.
reaching as far as the Punjab plains. The other branch  Over the N.E. portion of peninsular India, the two
moves up the Brahmaputra valley in the north and the branches also intermittently collide, creating weak
northeast, causing widespread rains. Its sub-branch weather fronts with sufficient rainfall to produce
strikes the Garo and Khasi hills of Meghalaya. patches of fairly high precipitation (more than 152 cm)
 The hills of Garo, Khasi and Jaintia are expanded in a in the Chhotanagpur plateau.
funnel shape with an opening towards the sea. So, the
moist winds coming from the Bay of Bengal undergo a 4. RETREATING MONSOON OR N.E. MONSOON SEASON
sudden rise here and cause excessive rainfall.  The S.W. monsoons start retreating in the first
Mawsynram (altitude 1,400 m), located on the southern week of September from Pakistan's border in
slopes of Khasi hills, receives the highest average annual North-West India. Thus, these winds withdraw
rainfall in the world (1,187 cm). earlier from the regions they reached the last.
 There is relatively less rainfall on the leeward slope of  The monsoon retreats from the W. Rajasthan by
the Meghalaya Plateau, e.g. 363 cm in Shillong and 303 the first week of September. It withdraws from
cm in Guwahati. The Brahmaputra valley to the north Rajasthan, Gujarat, Western Ganga plain and the
also experiences a rain-shadow; the problem is Central Highlands by the end of the month.
mitigated, however, by the adjacent Himalayas, which  By the beginning of October, the low pressure
cause the winds to rise again, thereby establishing a covers northern parts of the Bay of Bengal and by
parallel belt of heavy precipitation. early November, it moves over Karnataka and
Note Tamil Nadu. By the middle of December, the
 The Arabian Sea branch is stronger than the Bay of centre of low pressure is completely removed from
Bengal branch. Reasons: the Peninsula.
 The Arabian Sea is larger than the Bay of  As discussed earlier, unlike the sudden burst of the
Bengal. advancing monsoons, the withdrawal is rather
 The entire Arabian Sea current advances
gradual and takes about three months.
towards India, whereas only a part of the Bay
of Bengal current enters India, the remainder

https://strgk.on-app.in/app/oc/466231/strgk?utm_source%3Dwhatsapp%26

Prepared by ARGHYA SIR 9

 The Indian Climate

 The breaks are believed to be brought about by the

northward shifting of the monsoon trough (minimum low
pressure cell in ITCZ). The axis of the trough lies at the
foothills of the Himalayas during the break period. During
the break period, heavy rainfall occurs over the sub-
Himalayan regions and the southern slopes of the
Himalayas.
 These breaks in rainfall are also related to the cyclonic
depressions mainly formed at the head of the Bay of
Bengal, and their crossing into the mainland.
The Withdrawal of the S.W. Monsoon
 October-November form a period of transition from the
hot rainy season to the dry winter conditions.
 The withdrawal of the S.W. monsoon and the onset of
the N.E. Monsoon in the end of September are a gradual
phenomenon. They take place almost at the same time
and tend to merge. This is called Retreating Monsoon.
 It happens due to the weakening of the low-pressure
Temperature Conditions area over N.W. parts of India (and thus a gradual
 This season is marked by clear skies and a rise in transition of ITCZ towards the south). This happens due
temperature. The land is still moist. Owing to the to:
conditions of high temperatures (around 25°C) and  The apparent shift of sun towards the equator.
humidity, the weather becomes rather oppressive and  Reduction in temperature due to widespread rains.
unbearable. This is commonly known as the 'October
heat' or 'Kwarki Umas'. CLIMATIC REGIONS OF INDIA
 In the second half of October, the mercury begins to fall
rapidly, particularly in N. India. This continuous decrease
in temperature after mid-October helps winter to set in
by November or Early December.
However, October-November is the main rainy season in
Tamil Nadu and adjoining areas of Andhra Pradesh to the
south of the Krishna delta as well as a secondary rainy
period for Kerala. The retreating monsoons absorb
moisture while passing over the Bay of Bengal and cause
this rainfall.
IMPORTANCE OF MONSOON FOR INDIA
 Indian monsoon plays vital role in India's attempt to
achieve food security. More than 50% Indian population
depend on agriculture for their livelihood, which is based
on S.W. monsoon.
 Nearly 55% of the country's farms lack irrigation facilities,
leaving millions of farmers dependent on the rains.
 Monsoon is critical to replenish reservoirs necessary for
power generation, irrigation and drinking.
 Monsoon regime emphasizes the unity of India with the
rest of S.E. Asian region.
Break in the Monsoon
 During the S.W. monsoon period, if rain fails to occur for
one or more weeks, it is known as 'break' in the
monsoon. These dry spells are quite common during the
rainy season.

Prepared by ARGHYA SIR 10

https://strgk.on-app.in/app/oc/466231/strgk?utm_source%3Dwhatsapp%26
 The Indian Climate

 India is often referred to as a country with tropical type) Cwg Rajasthan

monsoon type of climate. However, the large latitudinal (Monsoon type Most parts of the 100-200 cm
extent, the presence of Himalayas in the north, the with dry Ganga Plain,
India Ocean in the south have resulted in great winters) eastern
Rajasthan, Assam
variations in the distribution of temperature and
and in Malwa
precipitation in the India. Plateau
 The climate of north is different from that of south and Dfc (Cold, Humid Sikkim, Arunachal ̴ 200cm
so is the climate of east from that of the west. To study winters type Pradesh and part
the variations of climate in various parts, India is divided with shorter of Assam
into a large number of climatic regions of small size. summer)
Et (Tundra Mountain areas of Rainfall varies
Type) Uttarakhand. The from year to
KOPPEN'S CLASSIFICATION average year.
 Koppen's Classification of Climatic Regions of India (by temperature Precipitation
the German-Russian climatologist WladimirKöppen in varies from 0o to occurs in the
1884) is based on mean annual and mean monthly 10oC form of snow.
temperature and precipitation data. Koppen divided
India into nine climatic regions making use of his GENERALISED CATEGORISATION
 India can be divided into a number of climatic regions:
scheme.
 Tropical Rain Forests: Found in the west coastal plains, the
 Koppen's Scheme - Climatic Regions of India Western Ghats and parts of Assam. Characterized by high
Climate type Region Annual Rainfall temperatures throughout the year. Rainfall, though
Amw Western coastal over 300 cm
seasonal, is heavy- about 200 cm annually during May-
(Monsoon region, south of
type with of Mumbai November.
Mumbai short  Tropical Savanna Climate: In most of the peninsula region
dry winter except the semi-arid zone in the leeward side of the
season) Western Ghats. It is characterized by long dry weather
throughout winter and early summer and high
As Coromandel coast = 75-100 cm[wet temperature (above 18.2°c); annual rainfall varies from 76
(Monsoon Coastal Tamil winters dry
cm in the west to 152 cm in the east.
type with dry Nadu and summers]
season in high adjoining areas of  Tropical Semi-Arid Steppe Climate: It prevails in the rain-
sun period) Andhra Pradesh shadow belt running southward from Central Maharashtra
Aw Most parts of the 75 cm to Tamil Nadu in the leeward side of the Western Ghats
(Tropical peninsular and the Cardamom Hills. It is characterized by low rainfall
Savannah type plateau barring which varies from 38 cm to 72 cm, high temperature
BShw (Semi- Coromandel and
between 20oand 28.8oc
arid Steppe Malabar coastal
type) strips  Tropical and Subtropical Steppes: Large areas in Punjab,
BShw(Semi-arid Some rain shadow 12 to 25 cm Haryana, Western U.P. and Kutch region.
Steppe type) areas of Western  Temperature varies from 12 – 35oc
Ghats, large part The maximum temperature reaches up to 49oc The annual
of Rajasthan and rainfall, varying from 30.5-63.5 cm, is also highly
contiguous areas erratic.
of Haryana and
Gujarat
BWhw (Hot desertMost of western less than 12 cm

https://strgk.on-app.in/app/oc/466231/strgk?utm_source%3Dwhatsapp%26

Prepared by ARGHYA SIR 11

 The Indian Climate

 Tropical desert: This climate extends over the western annual mean temperature will reduce agricultural
parts of Barmer, Jaisalmer and Bikaner districts of productivity by 15-20%.
Rajasthan and parts of Kutch. It is characterized by scanty  Some reasons identified behind this shift in microclimatic
rainfall (30.5 cm), which is highly erratic. Rains are mostly zones is change in land-use patterns, deforestation,
in the form of cloud-burst. Mean monthly temperature is encroachments upon mangroves, disappearing wetlands
uniformly high (about 35oc ) . & natural ecosystems by encroachment, and urban heat
 Humid Subtropical Climate with Dry Winters: This area islands.
includes south of the Himalayas, east of the tropical and
subtropical steppes and north of tropical savannah. Why Is The Bay of Bengal So Prone To Cyclones?
Winters are mild to severe while summers are extremely  Though both BoB and Arabian Sea are located in the same
hot. The annual rainfall varies from 63.5 cm to more than latitude band and receive same amount of solar radiation,
125 cm, most of it received during the south west the BoB is much warmer than the Arabian Sea and many
monsoon season. more storms brew over the Bay.
 Mountain Climate: Such type of climate is seen in  When the two are compared, the BoB sees approx. five
mountainous regions which rise above 6,000 m or more times as many cyclones as its Western counterpart. In
such as the Himalayas and the Karakoram Range. addition, cyclones in the Bay are stronger and deadlier.
 And what's more, nearly 58% of cyclones formed in the
Bay of Bengal reach the coast as compared to only 25% of
MICROCLIMATIC ZONES
 The microclimate represents the climate conditions that those formed in the Arabian Sea.
prevail at a local scale, or in areas of limited size, such as
the immediate surroundings of plants and animals. It But Why is That?
generally differs from the prevailing regional climatic  Tropical cyclones are intense water-rotating systems
conditions. formed by strong winds (of speeds at least 62 km/hour)
around low-pressure areas. They have a spiral,
 For example, in a forest, dense foliage reduces the
amount of light reaching the ground. This also results in a anticlockwise movement. Additional weather conditions
changed air temperature profile. The day-time air like high Sea Surface Temperature (SST), small variations
in vertical wind speed, and high relative humidity help
temperature inside the forest is lower than outside. Also,
the interior of a forest may be more humid than a nearby cyclones form and intensify.
non-forested area.  Since SST and humidity both directly correlate with
chances of cyclone formation, BoB is a more likely target
 The microclimates of a region are defined by the moisture,
temperature & winds of the atmosphere near the ground, because it gets higher rainfall, and because the sluggish
the vegetation, soil, latitude, elevation and season. winds around it keep temperatures relatively high: about
28 degrees C around the year. Warm air currents enhance
 Another contributing factor of microclimate is the slope or
this surface temperature and aid in the formation of
aspect of an area. South-facing slopes in the NH and
cyclones.
north-facing slopes in the SH are exposed to more direct
sunlight than opposite slopes and are therefore warmer  In addition, BoB receives constant inflow of fresh water
for longer periods of time, giving the slope a warmer from the Ganga - Brahmaputra and major peninsular
microclimate than the areas around the slope. rivers. This means that the Bay's surface water keeps
SHIFTING OF MICROCLIMATIC ZONES getting refreshed, making it impossible for the warm
 These zones are shifting across various districts of India. A water to mix with the cooler water below, making it ideal
shift in microclimate zones may lead to severe disruptions for a depression (in the Arabian Sea, there is no such
across sectors. For example, every 2 degrees C rise in stabilizing effect).

https://strgk.on-app.in/app/oc/466231/strgk?utm_source%3Dwhatsapp%26

Prepared by ARGHYA SIR 12

 The Indian Climate

 Since a sea surface temperature of about 27°C is necessary

for convection to take place in the atmosphere; this
condition is satisfied in BoB, but not in much of the Arabian
Sea.
 On the other hand, the Arabian Sea receives stronger winds
that help dissipate the heat, and the lack of constant fresh
water supply helps the warm water mix with the cool
water, reducing the temperature.
 BoB basin is also host to cyclones that are formed
elsewhere but move towards the water body, esp. those
formed in the Pacific Ocean.

https://strgk.on-app.in/app/oc/466231/strgk?utm_source%3Dwhatsapp%26

Prepared by ARGHYA SIR 13