Indian climatic regions experience large variation in climate varying from region to region, due to its vast size. India experiences climate variation from four major climate groups. These can be further subdivided into seven climatic types.
Tropical rainy climatic group is one kind of climatic region that experience persistent high temperatures, which normally do not go below 18°C even in the coolest month. There are two climatic types, which fall under this group, namely tropical monsoon rain forest and tropical wet and dry climate. The Western Ghats, west coastal lowlands, and southern parts of Assam have this climate type. It is characterised by high temperatures throughout the year, even in the hilly regions. The rainfall in these regions is seasonal, but heavy and is above 200 cm a year. Most of the rain is received in the tenure from May to November, and is adequate for the growth of vegetation during the entire year. December to March is the dry months with very scanty rainfall. The heavy rain is responsible for the tropical wet forests in these regions that consist of a large number of species of animals. Most of the plateau of peninsular India enjoys tropical wet and dry climate, except a semi-arid tract to the east of the Western Ghats. Winter and early summer are extensive 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 Tamil Nadu receives rainfall during the winter months of October to December.
Dry climate group is another Indian climatic region, consisting of regions where the rate of evaporation of water is higher than the rate of moisture received through precipitation. It is subdivided into two climate types, namely tropical semi-arid steppe climate and tropical and sub-tropical steppe. A long stretch of land situated to the south of Tropic of Cancer and east of the Western Ghats and the Cardamom Hills experiences tropical semi-arid steppe climate. It includes the states of Karnataka, interior Tamil Nadu, western Andhra Pradesh and central Maharashtra. 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 in this region 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 enduring agriculture.
The region of tropical and sub-tropical steppe lies towards the east of the tropical desert running from Punjab and Haryana to Kathiawar. They experience the climate as transitional climate falling between tropical desert and humid sub-tropical, with temperatures, which are comparatively less extreme than the desert climate. The annual rainfall is between 30cm to 65 cm but is very unreliable and happens mostly during the summer monsoon season. Maximum temperatures in this region during summer can rise to 40°C. The vegetation mostly comprises short coarse grass. Some crops like jowar and bajra are also cultivated.
Humid sub-tropical climate group denotes the temperature during the coldest months to be between 18 and 0°C. It has one climatic subdivision in India, namely humid sub-tropical 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 250cm annually to the east and near the Himalayas. The winters are usually dry due to the land derived winter winds which blow descending 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 slow 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 and crops.
In the Himalayan Mountains the climate signifies a separate kind of regional climate in India. There, 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. The 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 is clearly noticeable in the region.
The northern side of the western Himalayas, also known as the trans-Himalayan belt, is dry, cold and generally wind swept. The vegetation is sparsely populated and stunted as rainfall is scanty and the winters are severely cold. Most of the rainfall is in the form of snow during late winter and spring months. The area to the south of the great Himalayan range is well protected from cold winds coming from interior of Asia during winter. The leeward side of the mountains receives less rain while the expanded slopes get heavy rainfall. The places situated between 1070 to 2290 m altitudes receive the heaviest rainfall.
However it decreases rapidly above 2290m. The great Himalayan range receives heavy snowfall during winter months of December to February at altitudes above 1500m. The diurnal range of temperature is also high in this region. The states of Jammu and Kashmir, Himachal Pradesh, Uttarakhand and Sikkim experience this kind of weather.
The Indian climatic regions bring about the variety in climatic conditions in different parts of India. Thus, each and every region of India has a diverse climatic condition to offer and this factor has been the most intense one in terms of developing tourism in Indian subcontinent.
