Why this matters now
The monsoon is central to Indian geography and the economy — its mechanism, onset/withdrawal, the two branches, and links to El Niño are all examined, and forecasts feature constantly in current affairs.
What drives the monsoon
The classical explanation is differential heating of land and sea: in summer the landmass heats faster, creating a low-pressure trough over north-west India that draws in moist sea winds. Modern explanations add the role of the shifting ITCZ (Inter-Tropical Convergence Zone), the Tibetan Plateau heating, the tropical easterly jet and the subtropical westerly jet, and ocean phenomena.
The south-west monsoon
The south-west (summer) monsoon (June-September) brings the bulk of India’s rainfall through two branches: the Arabian Sea branch and the Bay of Bengal branch. Rainfall distribution depends on relief — the windward Western Ghats and the north-east (Mawsynram/Cherrapunji) are very wet, while leeward and interior areas get less.
The north-east (retreating) monsoon
From October the monsoon retreats; winds reverse to blow from land to sea. The north-east monsoon picks up moisture over the Bay of Bengal and brings rain to the south-east coast (Tamil Nadu) in October-December — the main rainy season there.
Variability — El Niño and IOD
The monsoon is variable. El Niño (warming of the central/eastern Pacific) is often associated with weaker monsoons and drought risk, while La Niña tends to favour good rains. The Indian Ocean Dipole (IOD) also modulates the monsoon. This variability drives droughts, floods and agricultural risk.
UPSC angle
Know the differential-heating + ITCZ mechanism, the two SW branches (Arabian Sea/Bay of Bengal), the NE monsoon over Tamil Nadu, and the El Niño/La Niña/IOD links.
Frequently asked questions
What causes the Indian monsoon?
Seasonal differential heating of land and sea and the shifting ITCZ create pressure differences that reverse the winds, supplemented by jet streams and the Tibetan Plateau.
What is the difference between the south-west and north-east monsoon?
The south-west monsoon (June-Sept) brings most of India’s rain; the north-east (retreating) monsoon (Oct-Dec) brings rain mainly to Tamil Nadu’s south-east coast.
How does El Niño affect the monsoon?
El Niño is often associated with a weaker monsoon and a higher risk of drought, whereas La Niña tends to favour good rainfall.
Which areas receive the highest monsoon rainfall?
The windward Western Ghats and the north-east (e.g. Mawsynram/Cherrapunji) receive very high rainfall.