The natural environment is the primary determinant of different species of plants and animals that are present in a particular surrounding. Climate, for example, influences site location, subsistence and settlement patterns. Moreover, it influences crop patterns of a region. The environment mainly comprises various elements such as climate, weather, landscape, rivers, animals, plants, etc. However, of these, climate is instrumental in influencing the other characteristics of a region. With regard to the subcontinent, the term ‘monsoon’ (“the rains”), which implies the seasonal wind reversal, is the dominant feature of the climate. In fact, from the equatorial Maldives to the Mediterranean latitude regions of northern Kashmir, the climate of South Asia is dominated by the monsoon. The countries of South Asia include some of the wettest regions on earth as well as both hot and cold deserts.
For understanding the history, it is important to have a brief look at the climatic features of India. India’s regional climates vary from the desert of Rajasthan to the maximum rainy area on earth, the Shillong Plateau. Despite its tropical latitude (Tropic of Cancer), India experiences huge contrasts of both rainfall and temperature from region to region. Though, the terms –winter, spring, summer and autumn- are often used to describe climatic transition in India, but the seasons do not correspond to this progression of seasons in all regions. Factors such as humidity, aridity, etc. are also to be seen in relation to the hotness or coldness of the seasons. These vary from region to region and affect temperature. However, the climatic transition very much depends on the arrival of the monsoon, although regional climates are very strongly affected by altitude and physiographical factors, both natural and man made.
The seasonal and regional contrasts in rainfall are more striking than contrasts in temperature. Southwards from Mumbai, the coastal fringe of the Western Ghats intercepts the southwest monsoon winds from May to October, resulting in excess rainfall of 4,000 mm near the coast. The Western Ghats running parallel to the west coast produce a marked rain shadow effect. As a result, the total rainfall in the interior peninsula measures to rarely exceeding 800 mm until the east coast is reached. The rainfall increases towards the northeast producing over 1600 mm in West Bengal. Assam has recorded some of the highest rainfall totals in the world. The Shillong Plateau on an average receives over 20,000 mm of rainfall annually. Delhi in the 21 north records 600 mm annual rainfall whereas the rainfall decreases southwards in Rajasthan measuring a total of less than 100 mm.
Tamilnadu in southeastern India forms a rain-shadow area of the Western Ghats when the southwest monsoon brings rain to the west coast. This region receives most of its rain between October and December, when the northeast monsoon reasserts itself. On the contrary, a narrow strip of the Punjab, which lies on the foothills or lower slopes of the mountainous region, receives winter rain through depressions in the westerlies which prevail across northern India throughout the winter. Similarly, the climate of the entire Himalayan region is modified dramatically by altitude.