The climate of India is described as a monsoon type, which is found mainly in South and Southeast Asia. The word 'monsoon' is derived from the Arabic word 'mausim', which literally means seasons. The monsoon climate is characterised by the seasonal reversal of winds and the alternation of wet summers and dry winters. India's climate has a very important influence on its agriculture, economy, and the daily lives of its people.
Although India's overall climate is the monsoon type, there is great diversity within the country. From the freezing winters of Ladakh and the warm summers of Rajasthan to the heavy rainfall of the northeast and the dry climate of the interior, India's climate is a combination of many different regional climates. This chapter explains the factors that affect India's climate, the mechanism of the monsoon, the seasons of India, and the phenomenon of global warming.
The Tropic of Cancer passes through the middle of India, roughly dividing the country into the tropical zone in the south and the subtropical/temperate zone in the north. The areas south of the Tropic of Cancer are closer to the Equator and have higher average temperatures throughout the year, while the northern parts experience a wider variation in temperature between summer and winter.
The temperature in India decreases with altitude. The Himalayas in the north protect India from the cold winds coming from Central Asia and Siberia in winter, keeping northern India warmer than other areas at the same latitude. The high mountains also cause the summer monsoon winds to deposit their moisture as rainfall in the northern plains.
The pressure and wind systems of the earth, together with the jet streams, affect the climate of India. The western disturbances, which originate over the Mediterranean Sea and are brought into India by the westerly jet stream, cause the winter rainfall in northern India. The easterly jet stream affects the monsoon over the eastern parts of India.
The coastal areas of India, being near the sea, have a moderate climate, with lower temperature ranges between day and night and between summer and winter. This is called a maritime or oceanic influence. The interior regions, being far from the sea, experience a continental climate with higher temperature ranges.
Relief features such as mountains and plateaus affect the distribution of rainfall. For example, the Western Ghats cause heavy rainfall on their windward side (the western coast), while the leeward side (the eastern side) receives much less rainfall, leading to the rain shadow region.
The monsoon is caused by the differential heating of land and sea. During the summer, the land heats up faster than the sea, creating a low-pressure area over the interior of Asia and India. The air above the sea, which is at a higher pressure, moves towards the land as the southwest monsoon winds. These winds bring abundant moisture from the Indian Ocean and the Arabian Sea.
The Himalayas act as a barrier, forcing the moist monsoon winds to rise, cool, and shed their moisture as rain. The presence of the high-pressure area to the south of the Indian Ocean and the low-pressure area over the interior of Asia are important for the onset of the monsoon. The westerly and easterly jet streams also play a role in the shifting of the monsoon winds.
The Inter-Tropical Convergence Zone is a low-pressure belt that shifts northwards in the summer and southwards in the winter. In summer, the ITCZ shifts northwards and is responsible for the withdrawal and onset of the monsoon. The monsoon winds are attracted towards the low-pressure area created by the shifting of the ITCZ.
During winter, the weather is generally dry in most parts of India. The temperature decreases from south to north. The northern parts of India experience the coldest weather, with frost and snowfall in the Himalayas. The low-pressure conditions over the north are replaced by high pressure. Rainfall is mainly caused by the western disturbances, which originate over the Mediterranean Sea, bringing winter rain to northern India and the northeast.
During the hot weather season, the sun shines vertically over the northern hemisphere, and the temperature rises rapidly. The summer season is characterised by high temperatures, low humidity, and a hot, dry wind called the 'loo' in the northern plains. The highest temperature is recorded in the north-western parts of India. Localised thunderstorms called 'Kaal Baisakhi' occur in West Bengal and Assam, and 'Mango showers' occur on the west coast.
The southwest monsoon winds blow from sea to land and bring abundant rainfall. The monsoon winds divide into two branches — the Arabian Sea branch and the Bay of Bengal branch. The Arabian Sea branch strikes the western coast and is forced to rise over the Western Ghats, causing heavy rainfall on the windward side. The Bay of Bengal branch passes over the Bay of Bengal, strikes the eastern coast, and causes rainfall over the northeastern states. The monsoon rainfall provides water for agriculture and is crucial for the Indian economy.
During the retreating monsoon, the monsoon winds begin to withdraw from northern India, and the temperature rises. The weather is hot and humid in October and November, and this period is known as the 'October Heat'. The retreating monsoon winds pick up moisture from the Bay of Bengal and cause rainfall over the eastern coast, especially Tamil Nadu. The cyclone activity in the Bay of Bengal and the Arabian Sea also increases during this period.
The amount of rainfall varies greatly across India. The western coast and the northeastern India receive very heavy rainfall, exceeding 400 cm in some places. The interior of the country, especially Rajasthan and parts of the Deccan, receives very low rainfall. Some places in Rajasthan receive less than 20 cm of rainfall. The rain shadow region of the Deccan, on the leeward side of the Western Ghats, receives less rainfall.
In spite of the regional differences, the monsoon is a unifying bond for the people of India. The whole country — the farmers, the traders, the planners, and the common people — waits for the monsoon, and its success or failure determines the fortunes of the nation. The rivers, which are fed by the monsoon, are the lifelines of agriculture, and the cycle of seasons brings a rhythm to the life of the people. The monsoon, therefore, is the pulse of India.
| Factor | Effect |
|---|---|
| Latitude | Tropical south, subtropical north |
| Altitude | Temperature decreases with altitude; Himalayas block cold winds |
| Pressure and winds | Western disturbances cause winter rain |
| Distance from sea | Coastal areas moderate; interior continental |
| Relief features | Western Ghats cause rain shadow |
| Season | Period | Main Features |
|---|---|---|
| Cold Weather | Dec to Feb | Dry weather, low temperatures, western disturbances |
| Hot Weather | Mar to May | High temperatures, 'loo', local thunderstorms |
| Advancing Monsoon | Jun to Sep | Southwest monsoon, heavy rainfall |
| Retreating Monsoon | Oct to Nov | October heat, rainfall in Tamil Nadu |
| Name | Region | Description |
|---|---|---|
| Loo | Northern plains | Hot, dry summer wind |
| Kaal Baisakhi | West Bengal, Assam | Local thunderstorms in summer |
| Mango showers | West coast | Pre-monsoon showers for mangoes |
| October Heat | Northern India | Hot, humid weather in October |
The climate of India is a monsoon type, shaped by a combination of latitude, altitude, pressure and wind systems, distance from the sea, and relief features. The differential heating of land and sea, reinforced by the Himalayas and the jet streams, gives rise to the southwest monsoon, which brings most of India's rainfall. India experiences four distinct seasons — the cold weather, the hot weather, the advancing monsoon, and the retreating monsoon — each with its own characteristics. The distribution of rainfall is highly uneven, creating regions of abundance and scarcity. Above all, the monsoon acts as a unifying bond for the people of India, linking the farmer, the trader, the planner, and the citizen in a common dependence on the rhythm of the seasons. The study of climate is essential not only for geography but for understanding the very pulse of Indian life.