India's Climate

Chapter summary

India's climate is called "tropical monsoon" — combining the fundamental tropical character (heat and humidity at low latitudes) with the seasonal reversal of winds that defines the monsoon system. The monsoon is so central to Indian life that the Indian Meteorological Department's annual monsoon forecast affects stock markets, government spending decisions, agricultural planning, and even foreign policy debates.

The chapter explains: (1) The six factors affecting Indian climate — latitude, altitude, pressure and wind systems, distance from the sea, ocean currents, relief. (2) The monsoon mechanism — differential heating creating pressure differences that reverse seasonally. (3) The four-season pattern — Cold weather (Dec-Feb), Hot weather (Mar-May), Southwest monsoon (Jun-Sep), Retreating monsoon (Oct-Nov). (4) External influences — El Niño/La Niña, Indian Ocean Dipole, Western Disturbances. (5) Climatic regions — from tropical wet to cold arid. (6) Climate change impacts already visible — more variable monsoons, extreme rainfall events, heatwaves, Himalayan glacier retreat.

The chapter's central insight: India's climate is uniform in monsoon dependence but diverse in regional manifestation. A single climatic system serves the most populated and agriculturally important country in the world — and that system is becoming more unpredictable due to climate change.

Six factors of Indian climate

1. Latitude: Tropic of Cancer (23.5°N) divides India into nearly equal halves. Areas south are tropical; areas north are subtropical to temperate.
2. Altitude: Temperature decreases with altitude. Himalayan slopes can be cold/snowy even at low latitudes. Hill stations like Shimla, Darjeeling exist because of altitude.
3. Pressure and wind systems: Trade winds, westerlies, monsoon winds. Pressure systems (high pressure over Tibet in summer, low pressure over India in summer) drive the monsoon.
4. Distance from the sea: Coastal areas have moderate climate (oceans buffer temperature extremes). Inland areas have continental climate (hot summers, cold winters).
5. Ocean currents: Warm currents bring moisture (e.g., Bay of Bengal currents). Cold currents reduce rainfall.
6. Relief features: Himalayas block cold Central Asian winds in winter and force monsoon winds to rise (orographic rainfall). Western Ghats cause heavy rain on windward side, rain-shadow on leeward.

The monsoon mechanism

The monsoon is essentially a seasonal reversal of wind direction. It works through differential heating of land and ocean:

Summer (Southwest monsoon)

• The Indian landmass heats up much faster than the surrounding Indian Ocean (March-May);
• By June, a thermal low pressure develops over Northwestern India (Rajasthan, Gujarat) and adjacent Pakistan;
• The Indian Ocean remains relatively cooler, with high pressure over it;
• Air flows from high to low pressure — winds blow from the Indian Ocean toward the land;
• These winds, having traveled over the Indian Ocean, are laden with moisture;
• As they hit the Western Ghats, Himalayas, and other relief features, they rise and cool, condensing into rain;
• This is the Southwest Monsoon (June-September) — brings ~75% of India's annual rainfall.

The southwest monsoon's two branches

• Arabian Sea branch: Strikes Kerala coast (~1 June), moves north hitting Western Ghats, then proceeds northeast to cover Maharashtra, Gujarat, Madhya Pradesh, Rajasthan, North India. Heavy rain on Western Ghats; rain-shadow on Deccan plateau (Pune sees only ~700 mm vs Mumbai ~2,500 mm).
• Bay of Bengal branch: Strikes Northeast India and Bengal coast (early June). Moves up the Ganga Plains. Provides heavy rain to Northeast (Mawsynram, Cherrapunji), Bengal, Bihar, Eastern UP. Some moisture also reaches NWFP-Punjab.
• The two branches converge over Punjab and meet to give heavy rain to the entire Ganga Plains.

Winter (Northeast monsoon / Retreating monsoon)

• By September-October, the Indian landmass starts to cool down;
• The thermal low pressure weakens; pressure pattern reverses;
• Cool, dry air begins to flow out from the land toward the ocean;
• This is the Northeast Monsoon (or Retreating Monsoon), bringing dry weather to most of India;
• Exception: Tamil Nadu coast gets significant rain because these winds, while traveling over the Bay of Bengal, pick up moisture and shed it on the eastern coast. Tamil Nadu's wet season is October-December, opposite to the rest of India.

India's four seasons

External influences — ENSO, IOD, Western Disturbances

El Niño-Southern Oscillation (ENSO)

El Niño (warm phase) and La Niña (cool phase) of equatorial Pacific waters significantly affect Indian monsoon:

• El Niño typically WEAKENS the Indian monsoon — fewer rains, drought-like conditions. Major El Niño years: 1972, 1982-83, 1987, 1997-98, 2002, 2009, 2015 — most below-normal monsoons;
• La Niña typically STRENGTHENS the Indian monsoon — more rains, sometimes floods.

Indian Ocean Dipole (IOD)

Temperature difference between western Indian Ocean (Arabian Sea area) and eastern Indian Ocean (off Indonesia):

• Positive IOD — warmer western, cooler eastern — STRENGTHENS Indian monsoon;
• Negative IOD — opposite pattern — WEAKENS monsoon.

Western Disturbances

Extratropical storms originating in Mediterranean and moving eastward bring winter rain to North India (December-April). Crucial for rabi crops, especially wheat. ~4-6 strong WDs per winter on average.

Climatic regions of India

Using Koeppen's classification, India can be divided into climatic regions:

Extreme records:

• Wettest: Mawsynram (Meghalaya) — ~12,000 mm/year. Cherrapunji nearby holds the record for highest annual rainfall ever (26,461 mm in 1860-61);
• Driest: Jaisalmer (Thar Desert) — <150 mm/year;
• Hottest recorded: Phalodi, Rajasthan — 51°C (May 2016);
• Coldest recorded: Dras, Kashmir — minus 60°C (1995).

Climate change impacts on India

Climate change is already affecting India's climate:

• More variable monsoons — both within-season and across years;
• Increase in extreme rainfall events — heavy downpours leading to floods (Kerala 2018, Maharashtra 2021, Himachal 2023);
• Decrease in moderate rainfall days;
• More heat waves in duration and intensity (Phalodi 2016; multiple recent years);
• Himalayan glacier retreat — affecting river systems;
• Sea level rise — threatens coastal cities (Mumbai, Chennai, Kolkata);
• Shifts in agricultural zones;
• Vector-borne disease range changes.

India's response includes the National Action Plan on Climate Change (NAPCC), eight National Missions, the Panchamrit goals announced at COP26 (2030 targets), and the Net Zero by 2070 commitment.

NCERT exercise Q&A (with explanations)

UPSC / MPSC previous year questions on this chapter