Climatic regions of India
India has a large variation in climate from region to region, due to its vast size. India experiences climate from four major climate groups. These can be further subdivided into seven climatic types. For ecological regions, see Ecoregions of India, for Regions see List of regions of India.
Tropical wet (humid) climate group
The regions belonging to this group experience persistent high temperatures which normally do not go below 18°C even in the coolest month.
- Tropical wet (dry,humid)
The west coastal lowlands, the Western Ghats, and southern parts of Assam have this climate type. It is characterised by high temperatures throughout the year, even in the hills. The rainfall here is seasonal, but heavy and is above 78 cm in a year. Most of the rain is received in the period from May to November, and is adequate for the growth of vegetation during the entire year. December to March are the dry months with very little rainfall. The heavy rain is responsible for the tropical wet forests in these regions, which consists of a large number of species of animals.Evergreen forests are the typical feature of the region.
- Tropical wet and dry or savannah climate
Most of the plateau of peninsular India enjoys this climate, except a semi-arid tract to the east of the Western Ghats. Winter and early summer are long dry periods with temperature above 18°C. Summer is very hot and the temperatures in the interior low level areas can go above 45°C during May. The rainy season is from June to September and the annual rainfall is between 75 and 150 cm. Only central eastern Tamil Nadu falls under this tract and receives rainfall during the winter months of late November to January.
Dry climate group
- Tropical semi-arid (steppe) climate
A long stretch of land situated to the south of Tropic of Cancer and east of the western ghats and the Cardamom Hills experiences this climate. It includes Karnataka, interior and western Tamil Nadu, western Andhra Pradesh and central Maharashtra.This area receives minimal rainfall due to being situated in the rainshadow area. This region is a famine prone zone with very unreliable rainfall which varies between 40 to 75 cm annually. Towards the north of Krishna River the summer monsoon is responsible for most of the rainfall, while to the south of the river rainfall also occurs in the months of October and November. The coldest month is December but even in this month the temperature remains between 20°C and 24°C. The months of March to May are hot and dry with mean monthly temperatures of around 32°C. The vegetation mostly comprises grasses with a few scattered trees due to the rainfall. Hence this area is not very well suited for permanent agriculture.
- Sub-tropical arid (desert) climate
Most of western Rajasthan falls under this climate type characterised by scanty rainfall. Cloud bursts are largely responsible for the all the rainfall seen in this region which is less than 30 cm. These happen when the monsoon winds penetrate this region in the months of July, August and September. The rainfall is very erratic and a few regions might not see rainfall for a couple of years. The summer months of May and June are very hot with mean monthly temperatures in the region of 35°C and highs which can sometimes reach 50°C. During winters the temperatures can drop below freezing in some areas due to cold wave. There is a large diurnal range of about 14°C during summer which becomes higher by a few more degrees during winter. This extreme climate makes this a sparsely populated region of India.
- Sub-tropical semi-arid (steppe) climate
The region towards the east of the tropical desert running from Punjab and Haryana to Kathiawar experiences this climate type. This climate is a transitional climate falling between tropical desert and humid sub-tropical, with temperatures which are less extreme than the desert climate. The annual rainfall is between 30 to 65 cm but is very unreliable and happens mostly during the summer monsoon season. Maximum temperatures during summer can rise to 40°C. The vegetation mostly comprises short coarse grass. Some crops like jowar and bajra are also cultivated.
Sub-tropical humid climate group
The temperature during the coldest months in regions experiencing this climate falls between 18 and 0°C.
- Sub-tropical humid (wet) with dry winters
The foothills of the Himalayas, Punjab-Haryana plain adjacent to the Himalayas, Rajasthan east of the Aravalli range, Uttar Pradesh, Bihar and northern part of West Bengal and Assam experience this climate. The rainfall is received mostly in the summer and is about 65 cm in the west and increases to 250 cm annually to the east and near the Himalayas. The winters are mainly dry due to the land derived winter winds which blow down the lowlands of north India towards the Bay of Bengal. The summers are hot and temperatures can reach 46°C in the lowlands. May and June are the hottest months. Winter months are mostly dry with feeble winds. Frost occurs for a few weeks in winter. The difference in rainfall between the east and the west gives rise to a wide difference in the natural vegetation.
- Mountain climate or highland climate or alpine climate
In the Himalayan mountains the temperature falls by 0.6°C for every 100 m rise in altitude and this gives rise to a variety of climates from nearly tropical in the foothills to tundra type above the snow line. One can also observe sharp contrast between temperatures of the sunny and shady slopes, high diurnal range of temperature, inversion of temperature, and variability of rainfall based on altitude.
The northern side of the western Himalayas also known as the trans-Himalayan belt is arid, cold and generally wind swept. The vegetation is sparse and stunted as rainfall is scanty and the winters are severely cold. Most of the snowfall is in the form of snow during late winter and spring months. The area to the south of the Himalayan range is protected from cold winds coming from interior of Asia during winter. The leeward side of the mountains receive less rain while the well exposed slopes get heavy rainfall. The places situated between 1070 and 2290 m altitudes receive the heaviest rainfall and the rainfall decreases rapidly above 2290m. The great Himalayan range witnesses heavy snowfall during winter months of December to February at altitudes above 1500m. The diurnal range of temperature is also high.