The Indian monsoon
The word monsoon comes from the Arabic "mausim", meaning season. It is a seasonal reversal of winds. In summer the land heats more than the sea, low pressure forms over north-west India, and moist winds blow from the Indian Ocean towards the land.
- South-west monsoon (June–September): gives roughly three-quarters of India's annual rainfall. It normally sets in over Kerala around 1 June and covers the whole country by early to mid July. It has two branches: the Arabian Sea branch (heavy rain on the Western Ghats) and the Bay of Bengal branch (north-east India and the Ganga plains). Withdrawal starts from north-west India in September.
- North-east monsoon / retreating monsoon (October–December): gives much of the rain of Tamil Nadu and nearby coastal areas.
- Break in monsoon: a dry spell of days or weeks within the rainy season; long breaks harm standing crops.
- Western disturbances: winter rain in north-west India that helps rabi crops such as wheat.
Role in agriculture
Kharif crops (rice, maize, cotton, pulses, groundnut, millets) are sown with the onset of the south-west monsoon. Monsoon rain also recharges groundwater, fills reservoirs and tanks, and supplies moisture for rabi crops. A late onset, long breaks or early withdrawal cause drought; very heavy rain causes floods. El Niño (warming of the central and eastern Pacific) is often linked with weaker Indian monsoons. Because so much farming is rainfed, the monsoon has been called the real finance minister of India.
Key points
- SW monsoon: June–September; about 75% of annual rain; onset at Kerala around 1 June.
- NE monsoon: October–December; important for Tamil Nadu.
- Withdrawal begins from north-west India.
- El Niño years are often weak-monsoon years.
Exam tips
Questions test months, the state that benefits from the NE monsoon, the onset state, and the link between monsoon and kharif crops.
Common mistakes
- Saying the NE monsoon brings most of India's rain; the SW monsoon does.
- Linking western disturbances with kharif; they help rabi crops.