Climate of India — Core Concepts
Core Concepts
India's climate is predominantly tropical monsoon, a unique system driven by seasonal wind reversals. The most defining feature is the Southwest Monsoon (June-September), which brings over 75% of the country's annual rainfall, crucial for agriculture.
This occurs due to the intense heating of the Indian landmass in summer, creating a low-pressure zone that attracts moisture-laden winds from the Indian Ocean. The Himalayas act as a formidable barrier, trapping these winds and causing heavy orographic rainfall, especially in the Western Ghats and Northeast India.
The retreating monsoon (October-November), also known as the Northeast Monsoon, brings winter rainfall to the southeastern coast, particularly Tamil Nadu, as winds pick up moisture from the Bay of Bengal.
Beyond the monsoon, India experiences distinct seasons: a hot summer (March-May) with local phenomena like 'loo' and pre-monsoon showers ('Mango showers'), a cold winter (December-February) influenced by Western Disturbances bringing rain/snow to the north, and the two monsoon periods.
Key factors influencing this climate include India's latitudinal extent, altitude (Himalayas), pressure and wind systems, upper air circulation (jet streams), and oceanic phenomena like El Niño-La Niña and the Indian Ocean Dipole (IOD).
These global teleconnections can significantly impact the monsoon's strength and variability. Regional variations are stark, from the arid Thar Desert to the humid Northeast and the cold Himalayas. Climate change is exacerbating these variations, leading to more frequent extreme weather events like heatwaves, floods, and droughts, posing significant challenges to India's environment, economy, and society.
Important Differences
vs Northeast Monsoon
| Aspect | This Topic | Northeast Monsoon |
|---|---|---|
| Period | June to September | October to December |
| Origin of Winds | Moisture-laden winds from the Indian Ocean (Arabian Sea & Bay of Bengal) | Retreating winds from landmass, picking up moisture from Bay of Bengal |
| Direction of Winds | Southwest to Northeast (sea to land) | Northeast to Southwest (land to sea, then sea to land over Bay of Bengal) |
| Affected Regions | Most of India, especially Western Ghats, Northeast India, Northern Plains | Southeastern Peninsular India (Tamil Nadu, Andhra Pradesh, parts of Kerala) |
| Rainfall Contribution | 75-80% of India's annual rainfall | Significant rainfall for specific regions, especially Tamil Nadu's annual quota |
| Driving Mechanism | Intense low-pressure over land (monsoon trough) and high-pressure over ocean; northward shift of ITCZ | High-pressure over land (cooling), southward shift of ITCZ; cyclonic depressions in Bay of Bengal |
| Associated Phenomena | Monsoon burst, orographic rainfall, breaks in monsoon | October Heat, tropical cyclones in Bay of Bengal |
vs Bay of Bengal Cyclones
| Aspect | This Topic | Bay of Bengal Cyclones |
|---|---|---|
| Frequency | More frequent (about 5-6 times a year) | Less frequent (about 1-2 times a year) |
| Intensity | Generally more intense and devastating | Generally less intense, but intensity is increasing due to climate change |
| Affected Coasts | East Coast (Odisha, West Bengal, Andhra Pradesh, Tamil Nadu) | West Coast (Gujarat, Maharashtra, Goa, Karnataka, Kerala) |
| Season of Formation | Pre-monsoon (April-May) and Post-monsoon (October-November) | Pre-monsoon (May-June) and Post-monsoon (October-December) |
| Causes of Higher Frequency/Intensity | Warmer sea surface temperatures, funnel shape of the Bay, higher freshwater influx, longer fetch for winds | Relatively cooler waters, smaller basin, less frequent favorable atmospheric conditions |
| Associated Phenomena | Heavy rainfall, storm surges, coastal flooding, wind damage | Similar impacts, but often less widespread initially |