The climate of India is described as a monsoon type of climate, although it shows great diversity within this broad description. India's climate is influenced by its location, physiography and the seasonal reversal of the winds. The monsoon, with its seasonal reversal of wind direction, dominates the climate of India and determines its agriculture, economy and the lives of its people. The word "monsoon" is derived from the Arabic word "mausim", meaning season.
India's climate varies from the hot and dry deserts of Rajasthan to the cold and snowy highlands of the Himalayas, and from the very wet regions of Meghalaya to the dry interiors of the Deccan. Factors such as latitude, altitude, distance from the sea, relief, and the pressure and wind systems together determine this diversity. In this chapter we study the unity and diversity of Indian climate, the mechanism of the monsoon, the seasonal rhythm of the climate, and the distribution of rainfall in India.
The unity of Indian climate lies in the dominance of the monsoon. From the northern plains to the southern peninsula, the monsoon winds bring rain in summer and the seasons follow a similar rhythm across the country. The seasonal reversal of winds, with the southwest monsoon in summer and the northeast monsoon in winter, unifies the climatic experience of India.
Despite this unity, India shows great diversity in climate: - Temperature: The temperature varies from below freezing in the Himalayas in winter to over 45-48 degrees Celsius in the Thar desert in summer. - Rainfall: The annual rainfall ranges from less than 15 cm in western Rajasthan to over 1,100 cm at Mawsynram in Meghalaya, one of the wettest places on Earth. - Seasonal variation: Some areas have heavy monsoon rain, others are drought-prone, and some experience snowfall in winter.
The Tropic of Cancer divides India into two parts: the tropical zone in the south and the subtropical zone in the north. The southern part is closer to the equator and has a tropical climate, while the northern part experiences subtropical climate with greater seasonal variation.
The Himalayas in the north act as a climatic barrier. They protect India from the cold winds of Central Asia in winter and cause the monsoon winds to give heavy rainfall in the plains. Altitude also causes cooler temperatures at higher elevations, such as in the Himalayan region and hill stations.
India lies in the region of the north-easterly trade winds in winter and the south-west monsoon winds in summer. The seasonal shifting of pressure belts and the position of the Inter-Tropical Convergence Zone (ITCZ) influence the monsoon.
Coastal areas like Mumbai and Chennai have equable (maritime) climates, while interior areas like Delhi and Rajasthan have extreme (continental) climates.
Warm and cold currents affect the coastal climate, and relief features like the Western Ghats cause orographic rainfall on their windward slopes.
The monsoon is a seasonal wind system with a complete reversal of direction. Several theories explain its mechanism: 1. Differential heating of land and sea: In summer, the land heats up faster than the ocean, creating a low pressure area over the interior of Asia and India. The moist winds from the Indian Ocean blow towards this low pressure, bringing the southwest monsoon. 2. Shift of the ITCZ: In summer, the ITCZ shifts northwards, drawing the equatorial westerlies and monsoon winds towards India. 3. The Himalayas: The high Himalayas block the cold winds of Central Asia and force the moisture-laden monsoon winds to rise and give rainfall. 4. Jet streams: The easterly jet stream and the shifting of the sub-tropical westerly jet stream influence the onset and progression of the monsoon. 5. El Nino and La Nina: El Nino (warming of the eastern Pacific Ocean) is associated with weaker monsoons in India, while La Nina is associated with better monsoons.
The year in India is divided into four main seasons: 1. The Cold Weather Season (Winter): From December to February. The sun is over the Tropic of Capricorn, and the days are short and nights are long. The north-east trade winds prevail, and the weather is dry and cool. The northern parts of India experience cold spells, with temperatures falling below freezing in the Himalayas. The northeast monsoon brings rainfall to the Tamil Nadu coast. 2. The Hot Weather Season (Summer): From March to May. The sun moves northwards, temperatures rise sharply, and a low pressure area develops over north-western India. Hot, dry, dusty winds called the Loo blow over the northern plains. Dust storms and thunderstorms (kalbaisakhi in Bengal) occur. 3. The Southwest Monsoon Season (Advancing Monsoon): From June to September. The moisture-laden southwest monsoon winds blow from the sea towards the land, bringing the main rainy season of India. The monsoon arrives in Kerala around 1 June and progressively moves northwards. The Mawsynram-Cherrapunji area receives the heaviest rainfall. 4. The Retreating Monsoon Season (Autumn): From October to November. The monsoon winds begin to withdraw, the weather becomes hot and humid, and the sky is clear. In early November, cyclonic depressions in the Bay of Bengal bring heavy rainfall to the Tamil Nadu coast (the "October heat" and northeast monsoon).
The average annual rainfall of India is about 125 cm, but it is unevenly distributed: - Very heavy rainfall (over 200 cm): The western coast and the north-eastern states, including Meghalaya. - Heavy rainfall (100-200 cm): Parts of the Ganga plain, the western coastal plain and the sub-Himalayan regions. - Moderate rainfall (50-100 cm): The central parts of the country. - Low rainfall (25-50 cm): The interiors of the Deccan plateau. - Very low rainfall (under 25 cm): The Thar desert of Rajasthan and parts of Gujarat.
| Season | Months | Characteristics |
|---|---|---|
| Cold weather (winter) | Dec-Feb | Dry, cool, north-east trade winds |
| Hot weather (summer) | Mar-May | High temperature, Loo, dust storms |
| Southwest monsoon | Jun-Sep | Main rainy season, SW monsoon winds |
| Retreating monsoon | Oct-Nov | Withdrawing winds, October heat, cyclones |
| Factor | Effect |
|---|---|
| Latitude | Tropical south, subtropical north |
| Altitude | Himalayas block cold winds, cause rainfall |
| Pressure and winds | Monsoon reversal, ITCZ shift |
| Distance from sea | Coastal equable, interior extreme |
| Relief | Western Ghats cause orographic rain |
The climate of India is essentially a monsoon climate, unified by the seasonal reversal of winds but diverse in its temperature and rainfall regimes. The climate is controlled by latitude, altitude, the pressure and wind systems, distance from the sea and relief. The monsoon mechanism, driven by differential heating of land and sea, the shifting ITCZ, the Himalayan barrier, jet streams and phenomena like El Nino and La Nina, brings the southwest monsoon that delivers most of India's rainfall. The year is divided into four distinct seasons: winter, summer, the southwest monsoon and the retreating monsoon. The uneven distribution of rainfall, from the wettest place on Earth in Meghalaya to the arid Thar desert, shapes India's agriculture, vegetation and economy.
Keywords: Monsoon, mausim, ITCZ, southwest monsoon, retreating monsoon, Loo, El Nino, La Nina, Mawsynram, seasonal reversal.