Climate & Indian Monsoon
Climate & Indian Monsoon
The monsoon system dominates Indian climate, delivering about 75% of annual rainfall during June-September through seasonal wind reversal. India spans climatic extremes from alpine cold in Ladakh to tropical conditions in Kerala, shaped by latitude, the Himalayan barrier, and ocean-atmosphere interactions. UPSC tests monsoon mechanism (ITCZ, ENSO, IOD), rainfall distribution, and Western Disturbances, while SSC/RRB asks about wettest/driest places, cyclone names, and seasonal phenomena.
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
Six factors shape India's climate. Latitude places the Tropic of Cancer across the middle, dividing tropical from subtropical zones. Altitude drops temperature at 6.5°C per 1,000 m, creating cool highlands alongside hot plains. Pressure and wind systems drive the monsoon through differential heating between the Indian landmass and ocean. Distance from the sea gives coastal areas equable/maritime conditions while interior regions experience continental extremes. Warm Indian Ocean currents load monsoon winds with moisture. Relief plays a decisive role: the Himalayas block cold Central Asian winds and trap moisture-laden monsoon air, forcing it upward to produce orographic rainfall, while the Western Ghats drench the windward (western) coast and cast a rain shadow over the leeward (eastern) Deccan.
The Monsoon Mechanism
Five mechanisms power the Indian monsoon. Differential heating between the subcontinent and Indian Ocean creates summer low pressure over the Thar Desert/Rajasthan while high pressure persists over the ocean, pulling moisture-laden winds landward as the South-West Monsoon. The ITCZ shifts northward over the Ganga Plain in summer, drawing Southern Hemisphere trade winds that the Coriolis effect deflects into SW Monsoon flow. El Nino (Pacific warming) typically weakens the monsoon and brings drought, while La Nina (Pacific cooling) strengthens it. A positive Indian Ocean Dipole (IOD) amplifies monsoon rainfall independently of ENSO. The Somali Jet and Tropical Easterly Jet add upper-level atmospheric controls. Two branches carry monsoon moisture: the Arabian Sea branch delivers heavier rainfall overall, while the Bay of Bengal branch advances up the Ganga valley.
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.