Climate refers to the average weather conditions of a region over a long period (usually 30+ years), including temperature, rainfall, humidity, and wind. India has a monsoon type of climate — dominated by seasonal reversal of winds and concentrated summer rainfall.
Factors Controlling India's Climate
Six key factors shape India's climate:
- 1.Latitude: The Tropic of Cancer divides India into tropical (south) and subtropical (north) zones. The south has higher temperatures year-round.
- 2.Altitude: Temperature decreases with altitude (approximately 6.5°C per 1000 m). Himalayas are cold; peninsular coasts are hot.
- 3.Pressure and winds: Seasonal changes in pressure create the monsoon.
- 4.Distance from the sea: Coastal areas have moderate temperatures (maritime effect); interiors have extreme temperatures (continental effect).
- 5.Ocean currents: Warm currents along coasts increase temperature and rainfall.
- 6.Relief (topography): Mountains force air to rise (causing orographic rainfall), block cold winds (Himalayas shield India from Central Asian cold).
The Indian Monsoon
- Example 1: Southwest Monsoon (June–September)
- As the Asian landmass heats up in summer, a low-pressure area develops over Rajasthan/Punjab. The moisture-laden southwest trade winds are drawn northward across the Indian Ocean. The monsoon arrives in two branches:
- Arabian Sea branch: Hits the Western Ghats, deposits heavy rain on the windward (western) side, then crosses to the Deccan Plateau as a dry, rain-shadow wind.
- Bay of Bengal branch: Moves up the Bay, enters northeast India (extremely heavy rain in Assam and Meghalaya), then turns west along the Gangetic plain.
Example 2: Orographic Rainfall on Western Ghats
The Arabian Sea monsoon hits the steep Western Ghats. Moist air rises, cools, and condenses — heavy rainfall on the western (windward) slope (Mumbai: 2200 mm/year). The eastern (leeward/rain shadow) side receives far less rain (e.g., Pune: 700 mm/year).
Example 3: Cherrapunji — World's Highest Rainfall
The Khasi Hills in Meghalaya (Mawsynram/Cherrapunji) funnel and lift the Bay of Bengal monsoon winds, causing annual rainfall of over 11,000 mm — among the world's highest. The geographic "bowl" shape concentrates moisture.
Example 4: Retreating Monsoon / Northeast Monsoon (October–December)
In October, the low-pressure system over northwest India weakens. The southwest monsoon retreats. Winds reverse direction (northeast monsoon). These winds pick up moisture over the Bay of Bengal and bring winter rains to Tamil Nadu and Andhra Pradesh's Coromandel Coast (when most of India is dry).
Example 5: Winter Season (December–February)
Winds blow from the continental interior (northwest and north) — cold and dry. Western disturbances (extra-tropical cyclones) from the Mediterranean bring winter rain to northwest India (Punjab, Haryana, Uttarakhand) and snowfall to the Himalayas. This is important for wheat cultivation.
Example 6: Pre-Monsoon / Summer Season (March–May)
Extreme heat builds over the interior. Loo — a hot, dry wind — blows in north-central India. Nor'westers (Kalbaisakhi) bring pre-monsoon showers to West Bengal and Assam — important for jute and tea. Mango showers in Kerala and Karnataka hasten mango ripening.
Example 7: Variability of Monsoon and Its Consequences
The monsoon is highly variable. A delayed or below-average monsoon causes drought; excessive rainfall causes floods. Both severely impact agriculture. India's vulnerability to monsoon variability is one reason why irrigation infrastructure is critical.
Seasons of India
| Season | Months | Key Features |
|---|---|---|
| Cold weather | Dec–Feb | Cold, dry, western disturbances |
| Hot weather | Mar–May | Loo, Nor'westers, mango showers |
| Southwest Monsoon | Jun–Sep | Main rainy season, 75% of annual rainfall |
| Retreating Monsoon | Oct–Nov | NE monsoon, rains in Tamil Nadu |
Key Concepts
- Monsoon: Seasonal reversal of wind direction causing wet/dry seasons.
- Western Disturbances: Extra-tropical cyclones from the Mediterranean bringing winter rain to NW India.
- Rain shadow: Leeward side of a mountain receiving little rain.
- Continentality: Wide temperature range due to distance from moderating ocean influence.
Common mistakes
Students often think India has just two seasons (summer and winter). India officially has four seasons: cold weather, hot weather, southwest monsoon, and retreating monsoon. Also, the northeast monsoon does NOT bring rain across all of India — it specifically brings winter rains to the Coromandel Coast (Tamil Nadu).
Summary
India's monsoon climate is controlled by latitude, altitude, relief, distance from the sea, and wind patterns. The southwest monsoon (June–September) brings 75% of India's annual rainfall. The northeast monsoon brings winter rain to Tamil Nadu. Temperature extremes are greatest in the interior (Thar Desert, north India) and most moderate along coasts. Understanding monsoon variability is key to understanding India's agriculture, water resources, and economy.