Climate & Indian Monsoon
Climate & Indian Monsoon
India has a tropical monsoon climate characterised by seasonal reversal of winds. The monsoon system is the dominant feature of Indian climate, bringing about 75% of annual rainfall during June-September. India experiences diverse climatic conditions — from alpine cold in Ladakh to tropical heat in Kerala.
Key Dates
South-West Monsoon typically arrives at Kerala coast (onset of monsoon)
Monsoon normally covers the entire country by mid-July
Monsoon begins retreating from north-western India
Retreating monsoon/North-East Monsoon — brings rain to Tamil Nadu coast
Receives highest average annual rainfall in the world (~11,871 mm), Meghalaya
Second highest average rainfall; holds record for highest rainfall in a single year (26,471 mm in 1860-61)
One of the driest places in India — receives less than 100 mm annual rainfall
India Meteorological Department (est. 1875) monitors and forecasts monsoon; HQ in New Delhi
Factors Influencing Indian Climate
Several factors shape India's climate: (1) Latitude — the Tropic of Cancer divides India into tropical and subtropical zones; (2) Altitude — temperature decreases with altitude at a lapse rate of about 6.5°C per 1,000 m; (3) Pressure and Winds — the monsoon system is driven by differential heating of land and sea creating pressure differences; (4) Distance from the Sea — coastal areas have equable/maritime climate, interior areas have continental/extreme climate; (5) Ocean Currents — the warm Indian Ocean current adds moisture to monsoon winds; (6) Relief/Topography — the Himalayas act as a barrier preventing cold Central Asian winds from entering India and trapping monsoon winds, forcing them to rise and cause orographic rainfall; Western Ghats cause heavy rainfall on the windward (western) side and rain shadow on the leeward (eastern) side.
The Monsoon Mechanism
The Indian monsoon is primarily driven by: (1) Differential heating between the Indian subcontinent and the Indian Ocean — in summer, the land heats faster, creating a low-pressure area (over the Thar Desert and Rajasthan), while high pressure persists over the Indian Ocean, causing moisture-laden winds to blow from sea to land (South-West Monsoon); (2) Shifting of the Inter-Tropical Convergence Zone (ITCZ) — the ITCZ shifts northward over the Ganga Plain in summer, attracting trade winds from the Southern Hemisphere, which get deflected to become the South-West Monsoon due to the Coriolis effect; (3) El Nino-Southern Oscillation (ENSO) — El Nino (warming of Pacific waters) generally causes weak monsoon/drought in India, while La Nina causes stronger monsoons; (4) Indian Ocean Dipole (IOD) — positive IOD increases monsoon rainfall; (5) Somali Jet and Tropical Easterly Jet also influence the monsoon. The monsoon has two branches: the Arabian Sea branch (brings more rainfall) and the Bay of Bengal branch.
Seasons of India
India experiences four seasons: (1) Cold Weather Season (Winter, December-February) — temperatures drop; NW India receives rainfall from Western Disturbances (temperate cyclones originating over the Mediterranean Sea); coldest month is January; Dras (Ladakh) is the coldest inhabited place in India; (2) Hot Weather Season (Summer, March-May) — temperatures rise rapidly; a low-pressure trough develops over the Thar Desert; "Loo" (hot, dry winds) blow over NW India; Nor'westers/Kalbaisakhi (thunderstorms) bring pre-monsoon showers to Assam, West Bengal; "Mango Showers" pre-monsoon showers in Kerala and Karnataka aid mango ripening; "Cherry Blossoms" in Karnataka aid coffee flowering; (3) South-West Monsoon/Advancing Monsoon (June-September) — brings about 75% of India's annual rainfall; onset over Kerala around June 1; the monsoon "bursts" suddenly; Arabian Sea branch hits Western Ghats first, Bay of Bengal branch moves up the Ganga valley; (4) Season of Retreating Monsoon (October-November) — NE Monsoon; cyclonic storms from Bay of Bengal hit Tamil Nadu and Andhra coast; Tamil Nadu receives bulk of its rainfall during this season.
Rainfall Distribution in India
India's average annual rainfall is about 118 cm. Distribution is highly uneven: (1) Areas of heavy rainfall (above 200 cm) — Western Ghats windward side, NE India (Meghalaya, Assam), Andaman & Nicobar Islands; Mawsynram (Meghalaya) receives the highest average annual rainfall in the world; (2) Moderate rainfall (100-200 cm) — most of the eastern plains, Western Ghats leeward side, eastern Madhya Pradesh; (3) Low rainfall (50-100 cm) — interior Deccan Plateau, Punjab, Haryana, upper Ganga plain; (4) Scanty rainfall (below 50 cm) — western Rajasthan (Thar Desert), Ladakh, parts of Gujarat and Tamil Nadu (rain shadow). About 11% of India is arid (less than 25 cm), 21% semi-arid. Tamil Nadu is unique — it receives rainfall mainly from the NE Monsoon (October-December), not the SW Monsoon. Koeppen classified India's climate into zones: Am (monsoon), Aw (tropical savanna), BSh (semi-arid), BWh (hot desert), Cwg (subtropical humid), and others.
Tropical Cyclones in India
India is vulnerable to tropical cyclones that originate over the Bay of Bengal and the Arabian Sea. Bay of Bengal cyclones are more frequent (about 5-6 per year) and more intense than Arabian Sea cyclones (about 1-2 per year). Peak cyclone seasons are: October-November (post-monsoon, primarily affecting east coast) and May-June (pre-monsoon). Major cyclone-prone states: Odisha, Andhra Pradesh, Tamil Nadu, West Bengal, and Gujarat. IMD classifies cyclones by wind speed: Deep Depression (49-61 km/h), Cyclonic Storm (62-87 km/h), Severe Cyclonic Storm (88-117 km/h), Very Severe Cyclonic Storm (118-167 km/h), Extremely Severe Cyclonic Storm (168-221 km/h), Super Cyclonic Storm (>221 km/h). Notable cyclones: Super Cyclone Odisha 1999 (deadliest in recent history), Cyclone Fani 2019 (Odisha), Cyclone Amphan 2020 (West Bengal), Cyclone Tauktae 2021 (Gujarat). Cyclone names are decided by WMO/ESCAP panel — India, Bangladesh, Pakistan, Sri Lanka, and other regional countries contribute names.
Relevant Exams
Climate and monsoon is a high-weight topic in UPSC Prelims (1-3 questions yearly). Questions on monsoon mechanism (ITCZ, ENSO, IOD), rainfall distribution, Western Disturbances, and Koeppen classification are common. SSC/RRB exams test factual recall — wettest/driest places, cyclone names, and seasonal phenomena. Current affairs questions often link monsoon variability, El Nino/La Nina events, and cyclone preparedness.