Climate of India – NDA Geography Notes

Introduction

India has one of the most fascinating climates in the world. A single country experiences everything — the freezing cold of Ladakh, the scorching heat of Rajasthan, the heavy rains of Cherrapunji, and the pleasant weather of Kashmir. All of this is governed by a complex set of factors — latitude, altitude, distance from the sea, and most importantly, the monsoon.

The monsoon is the backbone of India’s climate and economy. About 75% of India’s annual rainfall comes from the Southwest Monsoon between June and September. When the monsoon is good, crops are good and the economy grows. When it fails, droughts cause great suffering.

NDA tests this chapter through questions on monsoon mechanisms, El Niño effects, winter rainfall, the ITCZ, local winds, regional climate types, and specific rainfall data. These questions test both concepts and facts.

Understand the Topic

Factors Affecting India’s Climate

Several factors work together to shape India’s climate.

1. Latitude:
The Tropic of Cancer (23.5°N) passes through the middle of India. The south is tropical — hot throughout the year. The north is subtropical — with cooler winters and hotter summers.

2. Altitude:
Higher places are cooler. The Himalayas protect northern India from bitterly cold Central Asian winds in winter. Hill stations like Shimla and Darjeeling are much cooler than nearby plains.

3. Pressure and winds:
In winter, a high pressure belt forms over Central Asia. Cold, dry winds blow outward from this belt. The Himalayas block these winds from entering most of India.

In summer, intense heating of the Indian subcontinent creates a low pressure area. This draws in the moisture-laden Southwest Monsoon winds from the Indian Ocean.

4. Distance from the sea:
Coastal areas have moderate temperatures — neither very hot nor very cold. Places far from the sea (like Rajasthan) have extreme temperatures.

5. Ocean currents:
Warm waters of the Indian Ocean and the Bay of Bengal supply the moisture that the monsoon winds carry to India.

6. The Western Ghats:
These mountains act as a barrier to the Southwest Monsoon. The windward (western) side gets very heavy rain. The leeward (eastern) side is much drier — the rain shadow region.

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Why Does the Summer Monsoon Blow from the Southwest?

The summer monsoon winds blow from the southwest in the Northern Hemisphere because of the Coriolis force combined with the general direction of wind from the Indian Ocean. [NDA 2011-I]

The actual mechanism:

• In summer, the Indian landmass heats up strongly
• This creates a powerful low pressure area over northwest India
• Air from the high pressure zone over the southern Indian Ocean rushes toward this low pressure
• The Coriolis force deflects these winds to the right (northeastward) in the Northern Hemisphere
• So they arrive in India from the southwest direction

The primary driving factor is low pressure conditions in northwest India that draw in the moisture-laden winds. [NDA 2011-I]

The Monsoon

The word monsoon comes from the Arabic word “Mausim” meaning season. It refers to the seasonal reversal of winds. [NDA tested via CDS]

India has two monsoons:

Southwest Monsoon (June to September) — Summer Monsoon:
This is the main rainy season. It brings about 75% of India’s annual rainfall.

Northeast Monsoon (October to December) — Retreating Monsoon:
Affects mainly Tamil Nadu and the southeastern coast. Tamil Nadu gets most of its rain from the Northeast Monsoon, unlike the rest of India which depends on the Southwest Monsoon.

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Mechanism of the Southwest Monsoon

Step 1 — Heating of landmass:
From March onwards, the Indian subcontinent heats up rapidly. By June, an intense low pressure area develops over the Thar Desert in Rajasthan and the northwestern plains.

Step 2 — Shift of ITCZ:
The Inter-Tropical Convergence Zone (ITCZ) is a belt of low pressure near the equator where the trade winds from the two hemispheres meet. In summer, the ITCZ shifts northward over the Indian subcontinent — to roughly 20°–25°N. This shift is crucial for pulling the monsoon winds into India.

The ITCZ invites inflow of winds from different directions. [NDA 2012-II]

The statement that ITCZ forms “an important zone of contact over Northern India and Pakistan” is correct. [NDA 2012-II]

Step 3 — Monsoon winds arrive:
Moisture-laden winds from the Indian Ocean and the Bay of Bengal rush northward to fill the low pressure zone. These are the Southwest Monsoon winds.

Step 4 — Two branches of Southwest Monsoon:

The Southwest Monsoon splits into two branches when it hits the Indian subcontinent:

Branch	Entry Point	Areas Covered
Arabian Sea branch	Kerala coast	Kerala, Karnataka, Goa, Maharashtra, Gujarat, MP, Rajasthan
Bay of Bengal branch	Myanmar/Bangladesh coast	Northeast India, Bihar, UP, Delhi

Onset of Southwest Monsoon:

The monsoon first arrives on the Kerala coast around June 1. This is the official onset of the monsoon in India. [NDA tested via CDS]

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Rainfall Distribution in India

Rainfall in India is very uneven. Some places get too much; others get too little.

Highest rainfall areas:

• Cherrapunji (Sohra) and Mawsynram in Meghalaya — among the highest rainfall in the world (~11,000–12,000 mm per year). Both are in the Khasi Hills of Meghalaya.
• Mawsynram holds the record for the highest average annual rainfall in the world. [NDA tested via CDS]
• Agumbe in Karnataka — very high rainfall; called the “Cherrapunji of South India”
• Western coast, Western Ghats windward side, Northeast India

Lowest rainfall areas:

• Jaisalmer in Rajasthan — among the driest places in India
• Ladakh and western Rajasthan receive less than 100 mm per year
• Leh in Ladakh gets very little rain because it lies in the rain shadow of the Himalayas

Rainfall isohyets (lines joining places of equal rainfall):
The 50 cm isohyet (isohyetal line) roughly separates well-watered eastern India from the drier western India.

El Niño and Indian Monsoon

El Niño is a periodic warming of the central and eastern Pacific Ocean near Peru. When El Niño occurs:

• The surface temperature rises in the southern Pacific Ocean
• This disrupts the Walker Circulation (the normal east-west atmospheric circulation over the Pacific)
• The Walker Circulation shifts eastward from its normal position
• This reduces moisture supply to the Indian monsoon
• Result: Deficient rainfall in India — droughts or weak monsoon

Both of these effects of El Niño are correct: [NDA 2012-II]

1. Surface temperature goes up in the southern Pacific Ocean and there is deficient rainfall in India — TRUE
2. The Walker Circulation shifts eastward from its normal position and reduces monsoon rainfall — TRUE

So El Niño is associated with weak monsoon and drought conditions in India. [NDA 2012-II]

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Winter in India

Western Disturbances:

In winter (December to February), India’s northwest receives rainfall from a completely different source — Western Disturbances.

Western disturbances are cyclonic weather systems that originate in the Mediterranean Sea and travel eastward across Iran, Afghanistan, Pakistan, and into northwestern India. They bring winter rain and snowfall to:

• Jammu & Kashmir
• Himachal Pradesh
• Uttarakhand
• Punjab and Haryana (light winter rain)

This winter rainfall is very important for the Rabi crops (wheat, mustard, barley) grown in northern India in winter.

Tamil Nadu receives rainfall mainly in winter from the Northeast Monsoon — not the Southwest Monsoon. Most of Tamil Nadu is in the rain shadow of the Western Ghats, so it gets little rain from the Southwest Monsoon. But when the monsoon retreats, the winds become northeasterly and pick up moisture from the Bay of Bengal — bringing rain to Tamil Nadu between October and December.

Climate Seasons in India

India has four distinct seasons:

Season	Months	Key Feature
Winter	December to February	Cold, dry in north; Western Disturbances bring rain to NW India
Hot Weather (Summer)	March to May	Very hot; loo winds in north; dust storms
Advancing Monsoon	June to September	Heavy rainfall; SW Monsoon; 75% of annual rain
Retreating Monsoon	October to November	NE Monsoon; rain over Tamil Nadu

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Local Winds of India

Loo:
A hot, dry, and very strong wind that blows across the Indo-Gangetic Plain (northern India and Pakistan) in May and June. It blows from the west or northwest. Temperatures during Loo can exceed 45°C. Prolonged exposure causes heatstroke and death.

Kaal Baisakhi (Nor’wester):
Violent local thunderstorms that occur in West Bengal and Bangladesh during the late afternoon and evening in April and May (pre-monsoon season). They are associated with intense lightning, strong winds, and heavy rainfall. They are beneficial for Jute, Tea, and pre-Kharif crops in the region.

Mango Showers:
Pre-monsoon showers in Kerala and Karnataka that help in the ripening of mangoes. They occur just before the onset of the Southwest Monsoon.

Cherry Blossom / Coffee Showers:
Pre-monsoon showers in Karnataka that help flowering of coffee plants.

Blossom Showers:
Pre-monsoon rains in Kerala.

Monsoon Rainfall and Crops

India’s agriculture follows the monsoon. When monsoon fails, droughts hit and food production falls.

Kharif crops (sown in summer, harvested in autumn):

• Rice, maize, jowar, bajra, cotton, sugarcane, groundnut
• Depend heavily on the Southwest Monsoon

Rabi crops (sown in winter, harvested in spring):

• Wheat, mustard, barley, peas
• Depend on winter rain (Western Disturbances) and stored moisture

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South-West Monsoon — Key Facts for NDA

• The Southwest Monsoon blows from south-west to north-east in India
• It is caused primarily by low pressure conditions in northwest India [NDA 2011-I]
• The Coriolis force deflects the Indian Ocean winds to make them arrive from the southwest direction [NDA 2011-I]
• The ITCZ shifts north in summer — this is essential for the monsoon to penetrate deep into India [NDA 2012-II]
• El Niño shifts Walker Circulation eastward → less moisture for Indian monsoon → deficient rainfall [NDA 2012-II]
• Northeast Monsoon = retreating monsoon → mainly affects Tamil Nadu [NDA tested via CDS]