The Climate of India

The climate of India is described as the "Tropical Monsoon" type. This type of climate is found mainly in South and Southeast Asia.

1. Factors Influencing India's Climate

• Latitude: The Tropic of Cancer passes through the middle of India. The area to the north is in the subtropical zone, while the area to the south is in the tropical zone.
• Himalayas: Act as a climatic divide. They block the cold winds from Central Asia from entering India and trap the monsoon winds, causing heavy rainfall.
• Distance from the Sea: Coastal areas have a moderate climate (maritime), while interior areas have extreme climate (continental).
• Altitude: Temperature decreases with height. Hill stations like Shimla and Ooty are cooler than the plains.
• Upper Air Circulation (Jet Streams): The Subtropical Westerly Jet Stream (winter) and Tropical Easterly Jet Stream (summer) play a crucial role in the onset and withdrawal of monsoons.
• El Nino and La Nina: Periodic warming (El Nino) and cooling (La Nina) of the Pacific Ocean waters that influence monsoon patterns in India.
• Indian Ocean Dipole (IOD): The difference in sea surface temperature between the western and eastern Indian Ocean.

2. Mechanism of Indian Monsoon

Monsoon is a seasonal reversal of winds.

• Summer (SW Monsoon): High temperature over the land creates low pressure (Tibetan Plateau and NW India). The SE trade winds from the Southern Hemisphere cross the equator, get deflected to the right (Coriolis force), and enter India as South-West Monsoons.
• Onset: Usually occurs in early June on the Malabar coast.
• Branches:
  • Arabian Sea Branch: Causes heavy rain on the Western Ghats (windward side).
  • Bay of Bengal Branch: Heads towards the North-East and Northern Plains.
• Break in Monsoon: Periods of dry spells during the peak monsoon season.

3. The Seasons in India

1. Cold Weather Season (Winter - Dec to Feb): Clear skies, low temperatures. Western Disturbances from the Mediterranean cause light rain in North India (benefit for Rabi crops/Wheat).
2. Hot Weather Season (Summer - March to May): Rising temperatures. Pre-monsoon showers like Mango Showers (Kerala/Karnataka), Kal-Baisakhi (Bengal), Loo (hot dry winds in North).
3. South-West Monsoon Season (Rainy - June to Sept): General rainfall across India.
4. Retreating Monsoon/Transition (Oct to Nov): Monsoon winds retreat towards the Bay of Bengal. Causes cyclones on the eastern coast (Andhra/Tamil Nadu). October Heat is common.

4. Climatic Regions of India (Koppen's Classification)

• Amw: Monsoon type with short dry season (Western Coast).
• As: Monsoon with dry summer (Coromandel Coast - receives winter rain).
• Aw: Tropical Savanna (Peninsular Plateau).
• BShw: Semi-arid steppe (NW India).
• BWhw: Hot desert (Rajasthan).
• Cwg: Monsoon type with dry winters (Ganga Plain).
• Dfc: Cold humid winter with short summer (Arunachal Pradesh).
• E: Polar type (Himalayas).

5. Floods and Droughts

• India is prone to both due to the erratic nature of monsoons.
• Droughts: Occur when rainfall is deficient (El Nino years).
• Floods: Common in Ganga and Brahmaputra basins.