India’s climate, a complex system shaped by its vast geographical extent, is broadly classified as a Tropical Monsoon type. This classification masks profound diversity, ranging from arid deserts to cold alpine regions. While the seasonal wind reversal governs the rhythm of life for most of the country, regional variations in temperature and precipitation are significant.
Geographical and Atmospheric Controls
The Himalayas are the most significant physical feature influencing India’s climate. This colossal mountain range acts as a barrier, shielding the subcontinent from intensely cold, dry winds originating in Central Asia during winter. This sheltering effect keeps the northern plains warmer than other locations at similar latitudes.
The mountains also direct moisture-laden summer winds. As monsoon winds move inland, the Himalayan barrier forces them to rise, leading to cooling and copious rainfall across the northern plains and northeastern states. Without this orographic lifting mechanism, much of the subcontinent would experience a far drier climate.
India’s location astride the Tropic of Cancer introduces a fundamental climatic division. South of this line is the tropical zone, characterized by consistently high temperatures and a small annual range. The northern half, extending into the subtropical zone, experiences a continental climate with greater variation between summer heat and winter cold.
The surrounding water bodies—the Arabian Sea, the Bay of Bengal, and the Indian Ocean—provide the moisture reservoir for the monsoon system. Differential heating between the landmass and these oceans drives the seasonal wind reversal. This phenomenon creates the alternating low and high-pressure centers essential for the monsoons.
The Mechanism of the Monsoon Cycle
The annual monsoon cycle is a dynamic reversal of wind direction driven by shifting pressure systems over the subcontinent and the ocean. During summer, intense solar radiation causes the landmass, especially the vast Tibetan Plateau, to heat significantly. This heating creates a powerful, large-scale low-pressure system over the land, acting like a vacuum for the surrounding air.
The relatively cooler Indian Ocean retains higher atmospheric pressure, driving moisture-saturated air toward the low-pressure zone over the land. This influx of winds from the southwest is the Southwest or Summer Monsoon, typically beginning in June. This primary monsoon system is responsible for the vast majority of the total annual rainfall across India.
The Southwest Monsoon splits into two main branches as it approaches the peninsular tip: the Arabian Sea branch and the Bay of Bengal branch. The Arabian Sea branch moves north, providing heavy rainfall to the Western Ghats before moving across the central and western parts of the country. The Bay of Bengal branch brings rain to the northeastern states before turning westward across the Indo-Gangetic plains.
The contrasting phase is the Northeast or Winter Monsoon, occurring as the land cools rapidly from October onward. A high-pressure system develops over the cold Eurasian landmass, causing winds to reverse direction and blow from the northeast toward the warmer ocean. These continental winds are largely dry and do not bring widespread precipitation. However, as they pass over the Bay of Bengal, they pick up moisture, which is deposited as rain along the southeastern coast, particularly in Tamil Nadu and Andhra Pradesh, during the months of October to December.
Major Regional Climate Zones
The interaction of physical controls and the monsoon results in several distinct climate zones across the country. The Tropical Wet climate, characterized by high temperatures and abundant year-round rainfall, is found along the Konkan Coast and the Western Ghats. These regions support lush, dense evergreen forests.
The Deccan Plateau and eastern coastal plains fall under the Tropical Wet and Dry Savanna climate. This zone features a pronounced dry season followed by a wet summer monsoon, leading to vegetation adapted to seasonal water stress. Temperatures remain high, but annual rainfall is concentrated during the monsoon period.
The northwestern part of the country, particularly western Rajasthan, experiences an Arid climate, commonly known as the Thar Desert. Precipitation is extremely low, often less than 250 millimeters annually. Temperatures show a dramatic diurnal and annual range, with scorching summers exceeding 50 degrees Celsius in some areas. Bordering areas, including parts of Gujarat and the rain-shadow regions of the central plateau, are Semi-Arid, receiving slightly more but still insufficient rainfall.
The Indo-Gangetic plains are dominated by a Humid Subtropical climate. This region has hot, humid summers and cool, dry winters, with most precipitation arriving during the summer monsoon. The Himalayan states experience a Mountain or Alpine climate, where temperatures decrease significantly with altitude. These high-altitude regions are characterized by heavy winter snowfall and short, mild summers.
India’s Seasonal Progression
India’s climate is experienced through four distinct seasons recognized by the India Meteorological Department.
Cold Weather Season (December to February)
The year begins with the Cold Weather Season. Temperatures are lowest during this period, especially in northern India, where the mean daily temperature can drop below 15 degrees Celsius. In the northern plains, the weather is generally pleasant, with clear skies and low humidity. The extreme northwest experiences cold waves and occasional light winter rain from western disturbances. The peninsular region, being closer to the equator and surrounded by water, does not experience a true cold season, with temperatures remaining relatively high, often around 25 to 30 degrees Celsius.
Hot Weather Season (March to May)
The climate shifts into the Hot Weather Season as the sun moves northward, causing temperatures to rise rapidly across the country. Daytime temperatures in the northern and central plains frequently exceed 40 degrees Celsius, with areas in the northwest occasionally touching 45 to 50 degrees Celsius in May. This period is characterized by intense heat, low relative humidity, and the development of local hot, dry winds.
Rainy Season (June to September)
The arrival of the Southwest Monsoon in June heralds the Rainy Season. This season is marked by a sudden temperature drop and a dramatic increase in humidity as moisture-laden winds sweep across the land. The intensity of the rainfall varies significantly, with the Western Ghats and northeastern hills receiving over 2,500 millimeters, while regions like Rajasthan remain relatively dry.
Season of Retreating Monsoon (October to November)
This season marks the transition from wet to dry conditions. The low-pressure trough over the northern plains weakens and is replaced by a high-pressure system. This shift leads to clear skies and a rise in daytime temperatures, often called “October heat,” due to residual high humidity. The moisture from the Bay of Bengal during this period is responsible for the secondary rainfall maximum experienced by the southeastern coastal areas before the onset of the cool, dry winter.