India - Climate

CLIMATE - INDIA Page 1

CLIMATE – INDIA

1. UNITY AND DIVERSITY IN THE MONSOON CLIMATES

Indian climate → many regional variations; pattern of winds, temp. & rainfall, rhythm of

seasons, ° of wetness and dryness.

Summer* Rajasthan (55°C)

Winter* Leh, J&K (-45°C)

June day* Churu (RJ) [50°C<] / Tawang (AR) [<19°C]

December night* Drass (JK) [-45°C] / Trivandrum or Chennai [25°C]

KL and AN – difference of not more than 7-8°C

Thar desert – day (50°C); night (15°C - 20°C)

1.1 Regional Variations in precipitation

Cherrapunji & Mawsynram (ML) → 1080 cm yr⁄

Jaisalmer (RJ) → 9 cm yr⁄ (both of the same time period)

2. FACTORS DETERMINING THE CLIMATE OF INDIA

2.1 Location and Relief

2.2 Air pressure and Winds

2.1 Location and Relief

2.1.1 Latitude


Temperate / Sub – tropical zone (extreme climate)

Tropical zone (High temp. throughout the year)

2.1.2 The Himalayan Mountains

Protects the subcontinent from the cold northern winds.

Traps monsoon winds, forcing them to rain within the subcontinent.

2.1.3 Distribution of land and water

Differential heating of land & sea creates different air pressure zones in different

seasons.

Diff. in air pressure → reversal in direction of monsoon winds.

2.1.4 Altitude

Temp. decreases with height

Eg: Agra & Darjeeling located on the same latitude

Jan temp. Agra (16°C); Darjeeling (4°C)

2.1.5 Distance from the sea

Moderating influence of sea near the coastal areas.

Interior parts away from sea, so extreme climate in these areas.

2.1.6 Relief

Relief of an area affects the temp., air pressure, wind direction & speed, amt. &

distribution of rainfall.

Eg: Western Ghats


2.2 Air pressure and winds

Condition & pressure of winds → lower atmosphere

Upper air currents

Western disturbances & Tropical cyclones

2.2.1 Mechanism of Weather in Winter Season

2.2.1.1 Surface pressure & winds

High pressure in the N & Cen. Asia. Wind flows from N into India.

Come into contact with trade winds in NW India.

N India till mid – Ganga remains dry during winter.

2.2.1.2 Upper air circulation

Westerlies bifurcate in 2 by the Tibetan highland.

One flows over Tibet & another along S of Himalayas & plays role in winter.

2.2.1.3 Western disturbances & Tropical cyclones

Western cyclonic disturbances brought to India by Westerlies.

Tropical cyclone originates in the Bay of Bengal.

2.2.2 Mechanism of Weather in Summer Season

2.2.2.1 Surface pressure and winds

ITCZ shifts northwards.

Creates low pressure, air mass from the SH rush in from the SW direction.

2.2.2.2 Jet streams & upper air circulation

Westerlies withdraws, easterly sets in.

Up to 30°C.

2.2.2.3 Tropical cyclone

Easterly jet steers the tropical depression into India.

Easterly responsible for burst of monsoon in India.

3. THE NATURE OF INDIAN MONSOON

3.1 The onset of monsoon


3.2 Rain – bearing systems

3.6 Break in the monsoon

3.1 Onset of Monsoon

Differential heating of land & water; shifting of ITCZ in N; setting of easterly

& withdrawal of easterlies.

SW monsoon is continuation of SE trade winds deflected in Indian sub –

continent.

SE trade winds are attracted due to low pressure cause by the shifting of ITCZ,

cross equator, caught in circulation follow SW direction.

Easterlies responsible for burst of monsoon in India.

3.2 Rain – bearing systems & rainfall distribution

Intensity of rainfall over west coast due to:

a) Offshore meteorological conditions

b) Position of equatorial jet stream along the eastern coast of Africa

Movements of ITCZ cause fluctuations & intensity of these depressions.

3.3 Break in the Monsoon

SW monsoon after heavy spell of rain fails to occur. This is termed break in

the monsoon.

Quite common during rainy seasons. Occurs due to:

a) Storms not frequent along ITCZ over N India.

b) Wind blows parallel to the coast (W Coast)

4. THE RHYTHM OF SEASONS

4.1 Cold weather season

4.2 Hot weather season

4.3 SW monsoon season

4.4 Retreating monsoon season

Branches of SW monsoon

Bay of Bengal Arabian Sea


4.1 The Cold Weather season

4.1.1 Temperature

Sets by mid – Nov. in N India.

𝑥 daily temp. <21°C

Excessive cold caused due to

a) Away from the moderating influence of the seas.

b) Snowfall in the nearby Himalayas.

c) Cold winds from Cent. Asia.

4.1.2 Pressure & Winds

Feeble high pressure → N Plain.

Slightly low pressure – S Plains → leads to blowing of winds.

Weather is pleasant.

this is sometimes disturbed by cyclonic depressions from Mediterranean.

4.1.3 Rainfall

Does not cause much rainfall → have little humidity, anti – cyclonic

circulation on land.

Some parts are an exception:

a) In NW India, weak temperate cyclones cause rains.

b) Cent. parts of India & N parts of S peninsula.

c) AR & AS also get rains.

d) NW in TN, coastal AP

4.2 The Hot Weather Season

4.2.1 Temperature

April, May, June → Summer in N India

Extreme temp. due to temperate zones.

S India experiences mild temp. between 26°C - 35°C.

Ocean regulates the temp. here

4.2.2 Pressure and Winds


ITCZ moves N wards.

Due to this, it attracts a surface circulation of the winds.

These are equatorial Westerlies.

Dust storms common in NW regions.

Sudden local storms of great intensity – Loo

4.3 The South – West Monsoon Season

LP attracts trade winds of SH from the Indian Ocean.

These enter the Bay of Bengal & Arabian Sea.

Have moisture in abundance; move in a SW direction.

Begins rather abruptly → brings down the temp.

This sudden onset is called a ‘break’/’burst’.

Direction modified by relief & thermal low pressure over NW India.

Branches into 2.

Characteristics of Monsoon Rainfall

Seasonal in character → (June – Sept.)

Governed by relief & topography.

Has a declining trend with increasing distance.

Arabian Sea system

• Western Ghats

• Along Narmada & Tapivalleys, N mumbai

• Strike SaurashtraPeninsula, Kachchh, WRJ, PB along withAravalli

Bay of Bengal system

• Along the GangaValley

• Along theBrahmaputra valley


Kolkata (119 cm), Patna (105 cm), Allahabad (76 cm), Delhi (56 cm)

– SW monsoon

Occurs in wet spells & interspersed with rainless intervals know as

‘intervals’.

Summer rainfall is heavy leading to run off & soil erosion.

Plays a pivotal role in agriculture – ¾th of total rain received

during the SW monsoon.

Spatial distribution is uneven; Ranging from 12 – 250 cm.

Beginning of rain is delayed sometimes.

Sometimes ends considerably earlier than usual → causes damage

to crops.

4.4 Season of Retreating Monsoon

By the end of Sept. the SW monsoon becomes weak.

Retreats from W RJ followed by RJ, GJ, W Ganga plain & Central

Highlands.

By the beginning of Oct., the LP covers N parts of Bengal & by

early Nov. it moves over KA & TN.

By Dec. the center of LP is completely removed from the

Peninsula.

Marked by clear skies & rise in temp.

High temp. & humidity, known as October heat.

Heavy rain in the eastern part of Peninsula.

5. Distribution of Rainfall

The avg. annual rainfall in India is about 125 cm, but it has great

spatial variation.

a) Areas of high rainfall

Occurs along the W coast, on W Ghats, Sub – Himalayan areas in the NE & the

hills of Meghalaya.

Exceeds 200 cm.

In some parts i.e. Khasi & Jaintia, it exceeds >1000 cm.

Brahmaputra & adjoining valleys = <200 cm.

b) Areas of medium rainfall

S parts of GJ, E TN, NE peninsula covering OD, JK, BH, E MP, and N Ganga plains.

100 – 200 cm.


c) Areas of low rainfall

W UP, DL, HY, PB, JK, E RJ, GJ & Deccan Plateau.

50 – 100 cm

d) Areas of inadequate rainfall

Parts of the Peninsula (AP, KA, MH) Ladakh & W RJ.

<50 cm.

6. Climatic regions of India

i. Tropical climates → 𝑥 mth. temp. throughout the year is over 18°C.

ii. Dry climates → prec. is low compared to temp.

iii. Warm temperate climate → 𝑥 temp. of coldest mth. is between 18°C

– (- 3°C).

iv. Cool temperate climate → 𝑥 temp. of warmest mth. over 10°C &

coldest mth. under -3°C.

v. Ice climate → 𝑥 temp. of warmest mth. under 10°C.

7. Monsoon & the Economic Life in India

a. Entire agricultural cycle depends upon it. 64% of the population depends on

agriculture.

b. Regional variation helps in growth of a variety of crops.

c. Variability of rainfall → droughts / floods in parts of country.

d. Crops depend upon the timely arrival of monsoon.

e. Monsoon bursts creates prob. of soil erosion.

f. Winter rainfall (temperate cyclones) → benefits Rabi crops (N India).

g. Regional climatic variation reflects the variety in food, clothing, house types

etc.

ABBREVIATIONS

NE – North – East(ern) N – North

SE – South – East(ern) S – South

NW – North – West(ern) E – East

SW – South West(ern) W – West


KL – Kerala GJ – Gujrat

TN – Tamil Nadu RJ – Rajasthan

AP – Andhra Pradesh KA – Karnataka

OD – Odisha JK – Jammu & Kashmir

PB – Punjab JH – Jharkhand

BH – Bihar ML – Meghalaya

AR – Arunachal Pradesh AS – Assam

MP – Madhya Pradesh DL – Delhi

UP – Uttar Pradesh MH - Maharashtra

Cent. – Central 𝑥 = Mean

ITCZ – Inter – Tropical Convergence Zone

LP – Low pressure

Avg. – Average

Temp. – Temperature

Mth. – Month

* - Approximate values

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India - Climate