At a glance
PaperPaper ISubjectGeographyImportanceHigh
Book DigestGeographyNCERTIndia ClimateMonsoonJet StreamEl Nino
India has a tropical monsoon climate, dominated by the seasonal reversal of winds. The monsoon is the single most important feature of Indian geography and a perennial CAPF topic, because it governs agriculture, water and the economy.
- Differential heating of land and sea: in summer the landmass heats faster than the sea, creating a low-pressure trough over north-west India that draws in moist sea winds; in winter the reverse occurs.
- The apparent northward migration of the Sun shifts the Inter-Tropical Convergence Zone (ITCZ) north over India in summer, drawing the south-east trades across the equator, which (deflected right by the Coriolis force) become the south-west monsoon.
- The Tibetan Plateau heats intensely in summer, helping create an upper-air high that strengthens the circulation.
- Jet streams: the subtropical westerly jet lies south of the Himalayas in winter; its northward shift and break-up in early summer, and the establishment of the tropical easterly jet over peninsular India, are linked to the onset (the "burst") of the monsoon.
- El Nino and the Southern Oscillation (ENSO): warming of the central and eastern Pacific (El Nino) is associated with weak monsoons and drought in India; the La Nina phase tends to favour good rainfall. The Indian Ocean Dipole (IOD) also modulates the monsoon. (For year-specific monsoon outcomes, verify the latest from the IMD.)
| Season |
Months |
Features |
| Cold weather (winter) |
December to February |
Clear skies, low temperatures in the north; western disturbances (from the Mediterranean) bring rain to the north-west, useful for the rabi crop; the north-east monsoon gives the Tamil Nadu (Coromandel) coast its main rains. |
| Hot weather (summer) |
March to May |
Rising temperatures; the hot, dry Loo in the north; local storms such as the Kalbaisakhi (Nor'westers) in Bengal and mango showers in Kerala and Karnataka. |
| Advancing south-west monsoon (rainy) |
June to September |
The monsoon "bursts" around 1 June over Kerala, advancing in two branches; most of India's rain falls now. |
| Retreating monsoon (post-monsoon) |
October to November |
The monsoon withdraws; clear, humid weather ("October heat"); tropical cyclones form in the Bay of Bengal, hitting the east coast. |
- The Arabian Sea branch strikes the Western Ghats, giving very heavy rain on the windward (western) side and leaving a rain shadow on the Deccan interior; it also moves up to the plains.
- The Bay of Bengal branch moves up the Ganga plain and is deflected by the Himalayas westward; where it is forced up against the Khasi Hills, it produces the world's highest rainfall at Mawsynram and Cherrapunji (Sohra), Meghalaya.
- The two branches meet over the north-western plains.
- Highest: the windward Western Ghats and the north-east hills (Mawsynram, Cherrapunji).
- Lowest: western Rajasthan (Thar), Ladakh (a cold desert in the Himalayan rain shadow), and the interior Deccan rain shadow.
- The monsoon is marked by uncertainty, uneven distribution and breaks, which is why it is often called a gamble; drought and flood frequently occur in the same year in different regions.
The monsoon is central to food security and rural livelihoods: a failed monsoon raises food prices, rural distress and migration, with knock-on effects on internal stability. Monsoon floods (Assam, Bihar, Kerala) and post-monsoon cyclones (Odisha, Andhra) are recurring disaster-management challenges that mobilise the NDRF and the CAPFs. Climate change is altering monsoon intensity and variability, a live theme for the geography-environment essay.
- Onset over Kerala around 1 June; the two branches; why the windward Ghats are wet and the Deccan dry (rain shadow). Why Cherrapunji/Mawsynram is wettest.
- Western disturbances (winter rain in the north-west) and the north-east monsoon (Tamil Nadu's rain). El Nino and weak monsoon.
- The Loo, mango showers, Kalbaisakhi (Nor'westers) and which season each belongs to.
- The south-west monsoon normally sets in over which part of India first? (a) Mumbai (b) Kerala coast (c) West Bengal (d) Punjab. Answer: (b) Kerala coast, around 1 June. Authored practice, not a verbatim PYQ.
- Tamil Nadu receives most of its rainfall from which source? (Answer: the retreating / north-east monsoon, October to December.) Authored practice, not a verbatim PYQ.