60-second revision
- India has a tropical monsoon climate; the Himalayas block cold Central Asian winds.
- Monsoon onset over Kerala: around 1 June; covers the country by about early July.
- Western disturbances (from the Mediterranean region) bring winter rain to north-west India — good for rabi.
- Mango showers: Kerala/Karnataka; Kal Baisakhi: West Bengal and Assam; Loo: northern plains.
- Tamil Nadu coast gets much of its rain in October–December from north-east winds.
- Leeward side of the Western Ghats (e.g. Pune) is a rain-shadow area.
- El Nino often weakens the Indian monsoon; a positive Indian Ocean Dipole can help it.
What controls India's climate
- Latitude: the Tropic of Cancer divides India into a tropical south and a subtropical north.
- The Himalayas: block cold winds from Central Asia in winter and trap monsoon winds, forcing them to shed rain in the north.
- Distance from the sea: coastal areas have a moderate (maritime) climate; interiors are extreme (continental).
- Altitude: hill stations are cooler than plains at the same latitude.
- Pressure and winds, including the jet streams in the upper air and the reversal of winds between seasons — the very meaning of 'monsoon'.
The four seasons
| Season | Months (approx.) | Main features |
|---|---|---|
| Cold weather | December to February | North-east trade winds blow from land; clear skies; western disturbances bring rain and snow to the north-west; Tamil Nadu coast gets rain |
| Hot weather | March to May | Heat shifts north; Loo in the plains; pre-monsoon storms: mango showers, blossom showers, Kal Baisakhi |
| South-west monsoon (advancing) | June to September | Moist winds from the Indian Ocean bring most of India's annual rain; breaks in monsoon occur |
| Retreating monsoon (post-monsoon) | October to November | Winds withdraw; 'October heat'; cyclones in the Bay of Bengal hit the east coast |
How the monsoon works
In summer, intense heating creates a strong low-pressure area over north-west India, and the Inter Tropical Convergence Zone (ITCZ) shifts north over the Ganga plain. The south-east trade winds of the Southern Hemisphere cross the equator, are deflected to the right by the Coriolis force and arrive as south-west winds laden with moisture. A high-pressure area east of Madagascar, the Tibetan plateau's heating and the tropical easterly jet stream over peninsular India are also linked to the strength of the monsoon.
| Branch | Path and effect |
|---|---|
| Arabian Sea branch | Strikes the Western Ghats first, giving heavy rain on the windward side; the leeward Deccan interior gets far less. Part moves up to Gujarat and Rajasthan, where the Aravallis lie parallel to the winds and give little obstruction, so Rajasthan stays dry |
| Bay of Bengal branch | Strikes Myanmar and north-east India; the funnel-shaped Khasi hills give Mawsynram and Cherrapunji (Sohra) extremely heavy rain. Deflected by the Himalayas, it moves west up the Ganga plain, rainfall decreasing westwards |
Local storms of the hot season
| Name | Region | Usefulness |
|---|---|---|
| Mango showers | Kerala and coastal Karnataka | Help ripen mangoes |
| Blossom showers | Kerala and nearby coffee areas | Coffee flowers blossom |
| Kal Baisakhi (Nor'westers) | West Bengal and Assam | Useful for tea, jute and rice |
| Loo | Northern plains | Hot, dry, harmful winds |
Retreat and the winter rain of Tamil Nadu
From September the monsoon begins withdrawing from the north-west. Clear skies and moist ground cause the oppressive 'October heat'. As winds turn north-east, they cross the Bay of Bengal and bring rain to the Coromandel coast in October to December — the north-east (winter) monsoon. During the south-west monsoon this coast is relatively dry because it lies in the rain shadow of the Western Ghats and the winds blow parallel to it.
Variability of the monsoon
- El Nino: periodic warming of the central and eastern equatorial Pacific. Many Indian drought years have coincided with El Nino, though not every El Nino year is a drought.
- La Nina: the cooler phase, often linked with good monsoon rains.
- Indian Ocean Dipole (IOD): a positive IOD (warmer western Indian Ocean) generally supports the monsoon and can offset El Nino.
- Breaks: dry spells within the monsoon when the monsoon trough shifts towards the Himalayan foothills.
Test yourself: 10 questions, 35 s each
Every answer is explained. Free, no sign-up.
Start the quiz