Igp csat-paper-1-geography-gist-of-ncert-climate-

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Geography

GIST OF N.C.E.R.T

CLIMATE

Climate refers to the sum total of weather west direction. This, northern part of the India lies
conditions and variations over a large area for a in sub-tropical and temperate zone and the part
long period of time (more than thirty years). lying south of the Tropic of Cancer falls in the
Weather refers to the state of the atmosphere over tropical zone. The tropical zone being nearer to the
an area at any point of time. The elements of equ ator, ex peri ence s hi gh tempe ratu res
weather and cli mate are the same, i .e. throughout the year with small daily and annual
temperatu re, atmosph eric pressu re, wi nd, range. Area north of the Tropic of Cancer being
humidity and precipitation. You may have observed away from the equator, experiences extreme
that the weather conditions fluctuate very often climate with high daily and annual range of
even within a day. But there is some common temperature.
pattern over a few weeks or months, i.e. days are
Th e Himalayan Mou ntains: The to wering
cool or hot, windy or calm, cloudy or bright, and wet
mountain chain provides an invincible shield to
or dry. On the basis of the generalized monthly
protect the subcontinent from the cold northern
atmospheric conditions, the year is divided into
winds. The Himalayas also trap the monsoon
seasons such as winter, summer or rainy seasons.
winds, forcing them to shed their moisture within
During the summer season the desert area of the subcontinent.
Rajasthan witnesses 50º temperature whereas
Distribution of Land and Water: India is flanked
Pahalgam sector of Jammu and Kashmir has 20ºC
by the India Ocean on three sides in the south
temperature. During winter nights Dras sector of
and girdled by a high and continuous mountain-
Jammu and Kashmir witnesses– 45ºC temperature
wall in the north. As compared to the landmass,
where as Thiruvananth puram has 20ºC.
water heats up or cools down slowly. This
Rainfall also varies in terms of quantity and differential heating of land and sea creates
distribution in the regions of Himalaya rainfall is different air pressure zones in different seasons
in the from of snowy balls where as in the rest of in and around the Indian subcontinent. Difference
part of India it is a general rain. Again annual in air pressure causes reversal in the direction of
rainfall varies from 400ºC in the Meghalya to 10ºc monsoon winds.
in Ladakh and West Rajasthan. In the coastal area
Distance from the Sea: With a long coastline, large
the variation of rainfall is less. Whereas in the
coastal areas have an equable climate. Areas in
inner part of country the seasonal variation is
the interior of India are far away from the
more. Accordingly the Indians show their unity in
moderating influence of the sea. Such areas have
diversity in terms of food, clothing, housing and
extremes of climate. That is why, the people of
culture.
Mumbai and the Konkan coast have hardly any
Factors determining the climate of India idea of extremes of temperature and the seasonal
rhythm of weather. On the other hand, the
India’s climate is controlled by a number of factors
seasonal contrasts in weather at places in the
which can be broadly divided into two groups- (a)
interior of the country such as Delhi, Kanpur and
factors related to location and relief, and (b) factors
Amritsar affect the entire sphere of life.
related to air pressure and winds.
Altitude : Temperature decreases with height. Due
(a) Factors related to Location and Relief
to thin air, places in the mountains are cooler
Latitude: You know that the Tropic of Cancer than places on the plains. For example, Agra and
passes through the central part of India in east- Darjeeling are located on the same latitude, but

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Geography
temperature of January in Agra is 16ºC whereas Jet Stream and Upper Air Circulation: The pattern
it is only 4ºC in Darjeeling. of air circulation discussed above is witnessed only
at the lower level of the atmosphere near the
Relief: The physiography or relief of India also
surface of the earth. Higher up in the lower
affects the temperature, air pressure, direction and
troposphere, about three km above the surface of
speed of wind and the amount and distribution of
the earth, a different pattern of air circulation is
rainfall. The windward sides of Western Ghats and
observed. The variations in the atmospheric
Assam rece ive high rai nfal l du ring Jun e-
pressure closer to the surface of the earth have no
September whereas the southern plateau remains
role to play in the making of upper air circulation.
dry to its leeward situation along the Western Ghats.
All of Western and Central Asia remains under the
(b) Factors Related to Air Pressure and Wind influence of westerly winds along the altitude of 9-
To understand the differences in local climates of 13 km from west to east. These winds blow across
India, we need to understand the mechanism of the Asian continent at latitudes north of the
the following three factors: Himal ayas rou ghly parallel to the Tibetan
highlands. These are known as jet streams.
(i) Distribution of air pressure and winds on the Tibetan highlands act as a barrier in the path of
surface of the earth. these jet streams. As a result, jet streams get
(ii) Upper air circulation caused by factors bifurcated. On of its branches blows to the north of
controlling global weather and the inflow of the Tibetan highlands, while the southern branch
different air masses and jet streams. blows in an eastward direction, south of the
(iii)Inflow of western cyclones generally known as Himalayas. It has its mean position at 25ºN in
disturbances during the winter season and February at 200-300 mb level. It is believed that
tropical depressions during the south-west this southern branch of the jet stream exercise
monsoon period into India, creating weather an important influence on the winter weather in
conditions favourable to rainfall. India.
The mechanism of these three factors can be Western Cyclonic Disturbance and Tropical
understood with reference to winter and summer Cyclones: The western cyclone disturbances which
seasons of the year separately. enter the Indian subcontinent from the west and
the northwest during the winter months originate
Mechanism of Weather in the Winter
over the Mediterranean Sea and are brought into
Season
India by the westerly jet stream. An increase in
Surface pressure and winds: In winter months, the prevailing night temperature generally
the weather conditions over India are generally indicates an advance in the arrival of these
influenced by the distribution of pressure in cyclones disturbances.
Central and Western Asia. A high pressure centre
Tropical cyclones originate over the Bay of Bengal
in the region lying to the north of the Himalayas
and the Indian Ocean. These tropical cyclones
during winter. This centre of high pressure gives
have very high wind velocity and heavy rainfall
rise to the flow of air at the low level from the north
and hit the Tamil Nadu, Andhra Pradesh and Orissa
towards the Indian subcontinent, south of the
coast. Most of these cyclones are very destructive
mountain range. The surface winds blowing out of
due to high wind velocity and torrential rain that
the high pressure centre over Central Asia reach
accompanies it.
India in the form of a dry continental air mass.
These continental winds come in contact with Inter Tropical Convergence Zone (ITCZ)
trade winds over northwestern India. The position
of this contact zone is not, however, stable. The Inter Tropical Convergence Zone (ITCZ)
Occasionally, it may shift its position as far east is a low pressure zone located at the
as the middle Ganga valley with the result that equator where trade winds converge, and
whole of northwestern and northern India up to so, it is a zone where air tends to ascend.
the middle Ganga valley comes under the influence In July, the ITCZ is located around 20ºN
of dry northwestern winds. latitu des (ove r th e Gangetic plain ),


Geography

sometimes called the monsoon trough. This easterly jet stream steers the tropical depressions
mon soon tro ugh enco urag es the into India. These depressions play a significant
development of thermal low over north and role in the distribution of monsoon rainfall over
northwest India. Due to the shift of ITCZ, the Indian subcontinent. The tracks of these
the trade winds of the southern hemisphere depressions are the areas of highest rainfall in
cross the equator between 40ºE and 60ºE India. The frequency at which these depressions
longitudes and start blowing from southwest visit India, their direction and intensity, all go a
to northeast due to the Coriolis force. It long way in determining the rainfall pattern during
becomes southwest monsoon. In winter, the southwest monsoon period.
the ITCZ moves southward, and so the The Nature of Indian Monsoon
reversal of winds from northeast to south
Monsoon is a familiar, though a little known
and southwest, takes place. They are called
climatic phenomenon. Despite the observations
northeast monsoons.
spread over centuries, the monsoon continues to
Mechanism of Weather in the Summer puzzle the scientists. Many attempts have been
Season made to discover the exact nature and causation
of monsoon, but so far, no single theory has been
Surface Pressure and Winds: As the summer sets abl e to explain the mon soon ful ly. A re al
in and the sun shifts northwards, the wind breakthrough has come recently when it was
circulation over the subcontinent undergoes a studied at the global rather than at regional level.
complete reversal at both, the lower as well as the
upper levels. By the middle of July, the low pressure Systematic studies of the causes of rainfall in the
belt nearer the surface (termed as Inter Tropical South Asian region help to understand the causes
Convergence Zone (ITCZ) shifts northwards, and salient features of the monsoon, particularly
roughly parallel to the Himalayas between 20ºN some of its important aspects, such as:
and 25ºN. By this time, the westerly jet stream
(i) The onset of the monsoon.
withdraws from the Indian region. In fact,
meteorologists have found an interrelationship (ii) Rain-bearing systems (e.g. tropical cyclones)
between the northward shift of the equatorial and the relationship between their frequency
trough (ITCZ) and the withdrawal of the westerly and distribution of monsoon rainfall.
jet stream from over the North Indian Plain. It is
(iii) Break in the monsoon.
generally believed that there is a cause and effect
relationship between the two. The ITCZ being a Onset of the Monsoon
zone of low pressure attracts inflow of winds from Towards the end of the nineteenth century, it was
different directions. The maritime tropical air believed that the differential heating of land and
mass (mT) from the southern hemisphere, after sea during the summer months is the mechanism
crossing the equator, rushes to the low pressure
which sets the stage for the monsoon winds of drift
area in the general southwesterly direction. It is
towards the subcontinent. During April and May
this moist air current which is popularly known
when the sun shines vertically over the Tropic of
as the southwest monsoon.
Cancer, the large landmass in the north of Indian
Jet Streams and Upper Air Circulation: The Ocean gets intensely heated. This causes the
pattern of pressure and winds as mentioned above formation of an intense low pressure in the
is formed only at the level of the troposphere. An northwestern part of the subcontinent. Since the
easterly jet stream flows over the southern part of pressure in the Indian Ocean in the south of the
the Peninsula in June, and has a maximum speed landmass is high as water gets heated slowly, the
of 90 km per hour. In August, it is confined to 15ºN low attracts the southeast trades across the
latitude, and in September up to 22ºN latitudes. Equator. These conditions help in the northward
shift in the position of the ITCZ. The southwest
The easterlies normally do not extend to the north
monsoon may thus, be seen as a continuation of
of 30ºN latitude in the upper atmosphere.
the southeast trades deflected towards the Indian
Easterly Jet Stream and Tropical Cyclones: The subcontinent after crossing the Equator. These


Geography
winds cross the Equator between 40ºE and 60ºE EI-Nino and the Indian Monsoon
longitudes.
EI-Nino is a complex weather system that
The shift in the position of the ITCZ is also related appears once every three to seven years
to the phenomenon of the withdrawal of the bringing drought, floods and other weather
westerly jet stream from its position over the north extremes to different parts of the world.
Indian plain, south of the Himalayas. The easterly
Th e sy stem involves o cean ic and
jet stream sets in along 15ºN latitude only after
atmosph eric phe nome na w ith the
the western jet stream has withdrawn itself from appearance of warm currents off the coast of
the region. This easterly jet stream is held peru in the Eastern Pacific and affects
responsible for the burst of the monsoon in India. weather in many places including India. EI-
Entry of Monsoon into India: The southwest Nino is merely an extension of the warm
monsoon sets in over the Kerala coast by 1st June equatorial current which gets replaced
temporarily by cold Peruvian current or
and moves swiftly to reach Mumbai and Kolkata
Humbolt current (locate these currents in
between 10th and 13th June. By mid- July,
your atlas). This current increases the
so uthw e st monsoon engu lfs the enti re
temperature of water on the Peruvian coast
subcontinent.
by 10ºC. This results in:
Rain-bearing Systems and Rainfall (i) The distortion of equatorial atmospheric
Distribution circulation;
There seem to be two rain-bearing systems in (ii) Irregularities in the evaporation of sea
India. First originate in the Bay of Bengal causing water;
rainfall over the plains of north India. Second is
(iii) Reduction in the amount of planktons
the Arabian Sea current of the southwest monsoon
which further reduces the number of
which brings rain to the west coast of India. Much
fish in the sea.
of the rainfall along the Western Ghats is
orographic as the moist air is obstructed and forced The word EI-Nino means ‘Child Christ’
to rise along the Ghats. The intensity of rainfall because this cu rrent appears aro und
over the west coast of India is, however, related to Christmas in December. December is a
summer month in Peru (S outh ern
two factors:
Hemisphere).
(i) The offshore meteorological conditions.
EI-Nino is used in India for forecasting long
(ii) The position of the equatorial jet stream along range monsoon rainfall. In 1990-91, there
the eastern coast of Africa. was a wild EI-Nino even and the onset of
southwest monsoon was delayed over most
The fre quency of the tropical depressi ons
parts of the country ranging from five to
originating from the Bay of Bengal varies from year twelve days.
to year. Their paths over India are mainly
determined by the position of ITCZ which is Break in the Monsoon
generally termed as the monsoon trough. As the
During the south-west, monsoon period after
axis of the monsoon trough oscillates, there are having rains for a few days, it rain fails to occur for
fluctuations in the track and direction of these one or more weeks, it is known as break in the
depressions, and the intensity and the amount of monsoon. These dry spells are quite common
rainfall vary from year to year. The rain which during the rainy season. These breaks in the
comes in spells, displays a declining trend from different regions are due to different reasons:
west to east over the west coast, and from the
(i) In northern India rains are likely to fail if the
southeast towards the northwest over the North rain-bearing storms are not very frequent
Indian Plai n and the northern part of the along the monsoon trough or the ITCZ over this
Peninsula. region.


Geography
(ii) Over the west coast the dry spells are associated (i) States like Punjab, Haryana and Rajasthan
with days when winds blow parallel to the coast. bei ng far away from the moderating
influenced of sea experience continental
The Rhythm of Seasons
climate.
The climatic conditions of India can best be (ii) The snowfall in the nearby Himalayan ranges
described in terms of an annual cycle of seasons. creates cold wave situation; and
The meteorologists recognize the following four
seasons: (iii) Around February, the cold winds coming from
the Caspian Sea and Turkmenistan bring
(i) The cold weather season cold wave along with frost and fog over the
(ii) The hot weather season northwestern parts of India.

(iii) The southwest monsoon season The Peninsular region of India, however, does not
have any well-defined cold weather season. There
(iv) The retreating monsoon season.
is hardly any seasonal change in the distribution
pattern of the temperature in coastal areas
Some Famous Local Storms of Hot
because of moderating influence of the sea and
Weather Season
the proximity to equator. For example, the mean
(i) Mango Shower: Towards the end of max imum temperature for Jan uary at
summer. There are pre-monsoon showers Thiruvanantapuram is as high as 31ºC, and for
which are a common phenomena in Kerala June, it is 29.5ºC. Temperatures at the hills of
and coastal areas of Karnataka. Locally, they Western Ghats remain comparatively low.
are known as mango showers since they help
Pressure and Winds: By the end of December (22nd
in the early ripening of mangoes.
December), the sun shines vertically over the
(ii) Blossom Shower: With this shower, coffee Tropic of Capricorn in the southern hemisphere.
flowers blossom in Kerala and nearby areas. The weather in this season is characterized by
(iii) Nor Westers: These are dreaded evening feeble high pressure conditions over the northern
thunderstorms in Bengal and Assam. Their plain. In south India, the air pressure is slightly
notorious nature can be understood from the lower. The isobars of 1019 mb and 1013 mb pass
local nomenclature of ‘Kalbaisakhi’, a through northwe st I ndia and far sou th,
calamity of the month of Baisakh. These respectively.
showers are useful for tea, Jute and rice As a result, winds start blowing from northwestern
cultivation. In Assam, these storms are high pressure zone to the low air pressure zone
known as “Bordoiseela”. over the Indian Ocean in the south.
(iv) Loo: Hot, dry and oppressing winds Due to low pressure gradient, the light winds with
blowing in the Northern plains from Punjab a low velocity of about 3-5 km per hour begin to
to Bihar with higher intensity between Delhi blow outwards. By and large, the topography of the
and Patna. region influences the wind direction. They are
westerly or northwesterly down the Ganga Valley.
The Cold Weather Season They become northerly in the Ganga-Brahamputra
Temperature: Usually, the cold weather season delta. Free from the influence of topography, they
sets in by mid-November in northern India. are clearly northeasterly over the Bay of Bengal.
December and January are the coldest months in During the winters, the weather in India is
the northern plain. The mean daily temperature pleasant. The pleasant weather conditions,
remains below 21ºC over most parts of northern however, at intervals, get disturbed by shallow
India. The night temperature may be quite low, cyclonic depressions originating over the east
sometimes going below freezing point in Punjab Medirranean Sea and travelling eastwards across
and Rajasthan. West Asia, Iran, Afghanistan and Pakistan before
There are three main reasons for the excessive the reach the northwestern parts of India. On their
cold in north India during this season: way, the moisture content gets augmented from


Geography
the Caspian Sea in the north and the Persian Gulf moves further north, and in the north-western part
in the south. of India, temperatures around 48ºC are not
uncommon.
Role of Westerly Jet Stream
The hot weather season in south India is mild and
Rainfall: Winter monsoons do not cause rainfall
not so intense as found in north India. The
as they move from land to the sea. It is because
Pe ninsular situati on o f so uth Indi a wi th
firstly, they have little humidity; and secondly, due
moderating effect of the oceans keeps the
to anti cyclonic circulation on land, the possibility
temperatures lower than that prevailing in north
of rainfall from them reduces. So, most parts of
India. So, temperatures remain between 26ºC and
India do not have rainfall in the winter season.
32ºC. Due to altitude, the temperatures in the hills
However, there are some exceptions to it:
of Western Ghats remain below 25ºC. In the coastal
(i) In northwe stern In dia, some we ak regions, the north-south extent of isotherms
temperate cyclones from the Mediterranean parallel to the coast confirms that temperature
sea cause rainfall in Punjab, Haryana, Delhi does not decrease from north to south rather it
and western Uttar Pradesh. Although the increases from the coast to the interior. The mean
amount is meager, it is highly beneficial for daily minimum temperature during the summer
rabi crops. The precipitation is in the form of months also remains quite high and rarely goes
snowfall in the lower Himalayas. It is this below 26ºC.
snow that sustains the flow of water in the
Himalayan Rivers during the summer Pressure and Winds: The summer months are a
months. The precipitation goes on decreasing period of excessive heat and falling air pressure
from west to east in the plains and from north in the northern half of the country. Because of the
to south in the mountains. The average heating of the subcontinent, the ITCZ moves
winter rainfall in Delhi is around 53 mm. In northwards occupying a position centred at 25ºN
Punjab and Bihar, rainfall remains between in July. Roughly, this elongated low pressure
25 mm and 18 mm respectively. monsoon trough extends over the Thar desert in
(ii) Central parts of India and northern parts of the north-west to Patna and Chotanagpur plateau
southern Peninsula also get winter rainfall in the east-southeast. The location of the ITCZ
occasionally. attracts a surface circulation of the winds which
are southwesterly on the west coast as well as along
(iii) Arunachal Pradesh and Assam in the the coast of West Bengal and Bangladesh. They are
northeastern parts of India also have rains
easterly or southeasterly over north Bengal and
between 25 mm and 50 mm during these
Bihar. It has been discussed earlier that these
winter months.
currents of southwesterly monsoon are in reality
(iv) During October and November, northeast ‘displaced’ equatorial westerlies. The influx of these
monsoon while crossing over the Bay of winds by mid-June brings about a change in the
Bengal, pick up moisture and causes weather towards the rainy season.
torrential rainfall over the Tamil Nadu coast,
sou thern An dhra Pradesh , so uthe ast In the heart of the ITCZ in the northwest, the dry
Karnataka and southeast Kerala. and hot winds known as ‘Loo’, blow in the afternoon,
and very often, they continue to well into midnight.
The Hot Weather Season Dust storms in the evening are very common
Temperature: With the apparent northward during May in Punjab, Haryana, Eastern Rajasthan
movement of the sun towards the Tropic of Cancer and Uttar Pradesh. These temporary storms bring
in March, temperatures start rising in north India. a welcome respite from the oppressing heat since
April, May and June are the months of summer in they bring with them light rains and a pleasant
north India. In most parts of India, temperatures cool breeze. Occasionally, The moisture-laden
recorded are between 30º-32ºC. In March, the winds are attracted towards the periphery of the
highest day temperature of about 38ºC occurs in trough. A sudden contact between dry and moist
the Deccan Plateau while in April, temperature air masses gives rise to local storms of great
ranging between 38ºC and 43ºC are found in intensity. These local storms are associated with
Gujarat and Madhya Pradesh. In May, the heat belt violent winds, torrential rains and even hailstorms.


Geography
The Southwest Monsoon Season of low rainfall is known as the rain-shadow
area. Find out the rainfall at Kozhikode,
As a result of rapid increase of temperature in May Mangalore, Pune and Bangalore and note the
over the northwestern plains, the low pressure difference.
conditions over there get further intensified. By
early June, they are powerful enough to attract (ii) Another branch of the Arabian sea monsoon
the trade winds of Southern Hemisphere coming strikes the coast north of Mumbai. Moving
from the Indian Ocean/ These southeast trade along the Narmada and Tapi river valleys,
winds cross the equator and enter the Bay of Bengal these winds cause rainfall in extensive areas
and the Arabian Sea, only to be caught up in the of central India. The Chotanagpur plateau
air circulation over India. Passing over the gets 15 cm rainfall from this part of the
equatorial warm currents, they bring with them branch. Thereafter, they enter the Ganga
moisture in abundance. After crossing the equator, plains and mingle with the Bay of Bengal
they follow a southwesterly direction. That is why branch.
they are known as southwest monsoons. (iii) A third branch of this monsoon wind strikes
The rain in the southwest monsoon season begins the Saurashtra Peninsula and the Kachchh.
rather abruptly. One result of the first rain is that It then passes over west Rajasthan and along
it brings down the temperature substantially. This the Aravallis, causing only a scanty rainfall.
sudden onset of the moisture-laden winds In Punjab and Haryana, it too jokns the Bay
associated with violent thunder and lightening, is of Bengal branch. These two branches,
often termed as the “break” or “burst” of the reinforced by each other, cause rains in the
monsoons. The monsoon may burst in the first western Himalayas.
week of June in the coastal areas of Kerala, Monsoon Winds of the Bay of Bengal
Karnataka, Goa and Maharashtra while in the
interior parts of the country; it may be delayed to The Bay of Bengal branch strikes the coast of
the first week of July. The day temperature Myanmar and part of southeast Bangladesh. But
registers a decline of 5ºC to 8ºC between mid-June the Arakan Hills along the coast of Myanmar deflect
and mid-July. a big portion of this branch towards the Indian
subcontinent. The monsoon, therefore, enters
As the se w inds approach the l and, the ir West Bengal and Bangladesh from south and
southwesterly direction is modified by the relief southeast instead of from the south-westerly
and thermal low pressure over the northwest India. direction. From here, this branch splits into two
The monsoon approaches the landmass in two under the influence of the Himalayas and the
branches: thermal low is northwest India. Its one branch
(i) The Arabian Sea branch moves westward along the Ganga plains reaching
as far as the Punjab plains. The other branch moves
(ii) The Bay of Bengal branch.
up the Brahmaputra valley in the north and the
Monsoon Winds of the Arabian Sea northeast, causing widespread rains. Its sub-
branch strikes the Garo and Khasi hills of
The monsoon winds originating over the Arabian
Meghalya. Mawsynram, located on the crest of
Sea further split into three branches:
Khasi hills, receives the highest average annual
(i) Its one branch is obstructed by the Western rainfall in the world.
Ghats. These winds climb the slopes of the
Western Ghats from 900-1200 m. Soon, they Here it is important to know why the Tamil Nadu
become cool, and as a result, the windward coast remains dry during this season. There are
side of the Sahyadris and Western Coastal two factors responsible for it:
Plain receive very heavy rainfall ranging (i) The Tamil Nadu coast is situated parallel to
between 250 cm and 400 cm. After crossing
the Bay of Bengal branch of southwest
the Western Ghats, these winds descend and
monsoon.
get heated up. This reduces humidity in the
winds. As a result, these winds cause little (ii) It lies in the rain shadow area of the Arabian
rainfall east of the Western Ghats. This region Sea branch of the south-west monsoon.


Geography
Characteristics of Monsoonal Rainfall southward in response to the southward march of
the sun. The monsoon retreats from the western
(i) Rainfall recei ved from the sou thwe st
Rajasthan by the first week of September. It
monsoons is seasonal in character, which
withdraws from Rajasthan, Gujarat, Western
occurs between June and September.
Ganga plain and the Central Highlands by the end
(ii) Monsoonal rainfall is largely governed by relief of the month. By the beginning of October, the low
or topography. For instance the windward side pressures covers northern parts of the Bay of
of the Western Ghats register a rainfall of Bengal and by early November, it moves over
over 250 cm. Again, the heavy rainfall in the Karnataka and Tamil Nadu. By the middle of
northeastern states can be attributed to their December, the centre of low pressure is completely
hill ranges and the Eastern Himalayas. removed from the Peninsula.
(iii) The monsoon rainfall has a declining trend The retreating southwest monsoon season is
with increasing distance from the sea. marked by clear skies and rise in temperature.
Kol kata receive s 119 cm during the The land is still moist. Owing to the conditions of
southwest monsoon period, Patna 105 cm, high temperature and humidity, the weather
Allahabad 76 cm and Delhi 56 cm. becomes rather oppressive. This is commonly
(iv) The monsoon rains occur in wet spells of few known as the ‘October heat’. In the second half of
days, duration at a time. The wet spells are October, the mercury begins to fall rapidly,
interspersed with rainless interval known as particularly in northern India. The weather in the
‘breaks’. These breaks in rainfall are related retreating monsoon is dry in north India but it is
to the cyclonic depressions mainly formed at associated with rain in the eastern part of the
the head of the Bay of Bengal, and their Peninsula. Here, October and November are the
crossing into the mainland. Besides the rainiest months of the year.
frequency and intensity of these depressions, The widespread rain in this season is associated
the passage followed by them determines the with the passage of cyclonic depressions which
spatial distribution of rainfall. originate over the Andaman Sea and manage to
(v) The summer rainfall comes in a heavy cross the eastern coast of the southern Peninsula.
downpour leading to considerable run off and These tropical cyclones are very destructive. The
soil erosion. thickly populated deltas of the Godavari, Krishna
and Kaveri are their preferred targets. Every year
(vi) Monsoons play a pivotal role in the agrarian cyclones bring disaster here. A few cyclonic storms
economy of India because over three-fourths also strike the coast of West Bengal, Bangladesh
of the total rain in the country is received and Myanmar. A bulk of the rainfall of the
during the southwest monsoon season. Coromon dal coast is derived fro m th ese
(vii) Its spatial distribution is also uneven which depressions and cyclones. Such cyclonic storms
ranges from 12 cm to more than 250 cm. are less frequent in the Arabian Sea.

(viii) The beginning of the rains sometimes is Distribution of Rainfall
considerably delayed over the whole or a part The average annual rainfall in India is about 125
of the country. cm, but it has great spatial variations.
(ix) The rains sometimes end considerably Areas of High Rainfall: The highest rainfall occurs
earlier than usual, causing great damage to along the west coast, on the Western Ghats, as
standing crops and making the sowing of well as in the sub-Himalayan areas is the
winter crops difficult. northeast and the hills of Meghalaya. Here the
Season of Retreating Monsoon rainfall exceeds 200 cm. In some parts of Khasi
and Jaintia hills, the rainfall exceeds 1,000 cm.
The months of October and November are known In the Brahmaputra valley and the adjoining hills.
for retreating monsoons. By the end of September, The rainfall is less then 200 cm.
the southwest monsoon becomes weak as the low
pressure trough of the Ganga plain starts moving Areas of Medium Rainfall: Rainfall between 100-


Geography
200 cm is received in the southern parts of Gujarat,
east Tamil Nadu, northeastern Peninsula covering
Orissa, Jharkhand, Bihar, eastern Madhya
Pradesh, northern Ganga plain along the sub-
Himalayas and the Cachar Valley and Manipur.

Seasons Months Months
(According to the (According to the
India Calendar) Indian Calendar)

Vasanta Chaitra-Vaisakha March-April

Grishma Jyaistha-Asadha May-June

Varsha Sravana-Bhadra July-August

Sharada Asvina-Kartika September-October

Hemanta Margashirsa-Pausa November-December

Shishira Magha-Phalguna January-February

Areas of Low Rainfall: Western Uttar Pradesh,
Delhi, Haryana. Punjab, Jammu and Kashmir,
eastern Rajasthan, Gujarat and Deccan Plateau
receive rainfall between 50-100 cm.
Areas of Inadequate Rainfall: Parts of the
Pe ninsula, especially in A ndhra Pradesh,
Karnataka and Maharashtra, Ladakh and most of
western Rajasthan receive rainfall below 50 cm.
Snowfall is restricted to the Himalayan region.


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