The climate of India is one of immense complexity and contrast, defined by its sheer geographical scale. India’s climate, categorized broadly as a tropical monsoon type, is a composite of diverse regional variations that create a unique environmental profile. This continental-scale diversity is influenced by powerful atmospheric forces and massive physical barriers.
The Monsoon Mechanism
The defining feature of India’s climate is the monsoon, a dynamic system characterized by a complete seasonal reversal of wind direction. This atmospheric shift is primarily driven by the differential heating between the vast Indian landmass and the surrounding oceans. During the summer, the land heats up much faster than the Arabian Sea and the Bay of Bengal, creating an area of intense low pressure over the North Indian Plains and the Tibetan Plateau.
Cooler, high-pressure air over the Indian Ocean draws moisture-laden winds inward toward the continental low-pressure zone. These winds, deflected by the Coriolis effect, arrive from the southwest, marking the onset of the Southwest or Advancing Monsoon, typically starting in the first week of June in Kerala. As this humid air is forced upward by topography, it releases up to 80% of India’s annual rainfall between June and September.
The system reverses in the autumn as the sun shifts southward, causing the landmass to cool rapidly and replacing the low-pressure system with a high-pressure zone. Winds begin to blow from the land toward the sea, resulting in the Northeast or Retreating Monsoon, which is generally dry over most of the country. This retreating flow is only significant for the southeastern coast, particularly Tamil Nadu, where the winds pick up moisture from the Bay of Bengal before making landfall, providing the region with its main rainfall between October and December.
Primary Climatic Controls
India’s climatic patterns are fundamentally shaped by permanent geographical controls that determine temperature and precipitation distribution. The most significant control is the Himalayan mountain range, which acts as a massive barrier to frigid, dry winds sweeping south from Central Asia, keeping the northern plains considerably warmer in winter than other regions at similar latitudes. The Himalayas also force the incoming Southwest Monsoon winds to rise, condense, and precipitate.
The Tropic of Cancer, running nearly halfway through the country, divides India into a tropical zone in the south and a subtropical zone in the north. Regions south of this line experience more stable, consistently high temperatures throughout the year. North of the Tropic, areas exhibit a greater annual temperature range, with hotter summers and cooler winters.
Altitude and relief play an important role, as temperature decreases approximately \(6.5^{\circ}\text{C}\) for every 1,000 meters of ascent, creating temperate and alpine climates in the mountains. This orographic effect is evidenced by the stark contrast between the windward side of the Western Ghats, which receives heavy monsoon rainfall, and the leeward side, which lies in a drier rain-shadow zone. Distance from the sea dictates the degree of continentality; coastal cities like Mumbai experience a moderate climate, while inland cities like Delhi face climatic extremes of scorching summers and cold winters.
Major Seasonal Cycle
The India Meteorological Department (IMD) recognizes four distinct seasons. The Cold Weather Season, running from December to February, is defined by clear skies and low humidity across the northern plains, where mean temperatures can dip below \(10^{\circ}\text{C}\). This period is occasionally interrupted by Western Disturbances, low-pressure systems originating in the Mediterranean that bring light rainfall and snowfall to the Northwest.
The Hot Weather Season, spanning from March to May, sees temperatures rapidly rising as the thermal low-pressure area develops over the northwestern regions. Temperatures frequently exceed \(45^{\circ}\text{C}\) in the plains, accompanied by the localized, hot, and dry wind known as the Loo. This heat is sometimes relieved by pre-monsoon showers, such as the Mango Showers in the south, which aid in the ripening of local crops.
The Southwest Monsoon Season, from June to September, begins with the characteristic “burst” of monsoon rains, which lowers the ambient temperature by \(3^{\circ}\text{C}\) to \(6^{\circ}\text{C}\). This is the primary rainy season, characterized by high humidity and continuous cloud cover that significantly reduces the diurnal temperature range. The season is marked by “breaks” in rainfall, where dry spells alternate with wet periods.
The Season of Retreating Monsoon, covering October and November, is a transition phase marked by the gradual withdrawal of the monsoon winds. The clear skies following the retreat lead to a temporary rise in daytime temperatures combined with high residual humidity. This period also experiences the highest frequency of tropical cyclones forming in the Bay of Bengal, which often bring destructive rainfall to the eastern coastal states before the onset of winter.
Regional Climate Diversity
The immense size and varied physiography of India result in a mosaic of climatic regions that defy a single description. The extremes of temperature are vast, with the highest recorded temperature reaching \(51^{\circ}\text{C}\) in Phalodi, Rajasthan, contrasting with winter lows dropping to \(-40^{\circ}\text{C}\) in Dras, Ladakh.
In terms of precipitation, the Tropical Wet climate of the Northeast and the Western Ghats receives enormous annual rainfall. Mawsynram, Meghalaya, averages close to 11,871 mm, making it one of the wettest places on Earth. This contrasts sharply with the Arid and Semi-Arid regions of Western Rajasthan, such as Jaisalmer, which records less than 200 mm of rain per year.
The Alpine climate of the Himalayan regions, especially the trans-Himalayan belt of Ladakh, exists in a rain shadow, receiving minimal precipitation, primarily in the form of snow. Meanwhile, the interior Deccan Plateau experiences a Tropical Savanna or semi-arid climate, receiving moderate and highly variable rainfall, making it prone to drought.