Indian Monsoon
Published on 02 Feb 2025
The Indian monsoon is a seasonal wind system that brings rainfall to India and Southeast Asia from June to September. There are two main types of Monsoons in India Southwest Monsoon and Northeast Monsoon.
Significance of Indian monsoons
Rain fed agriculture and food security: 51% of Indian agriculture is rain fed timely arrival and distribution of monsoon rains are crucial for sowing and cultivation of crops and ensuring food security.
Recharge of water bodies: Monsoon rains contribute to the filling of rivers, lakes, and groundwater reservoirs. Adequate rainfall is essential for maintaining water levels and sustaining water resources.
Hydropower generation: Increased water flow in rivers during the monsoon season is essential for hydropower generation, contributing to the country's energy needs.
Temperature regulation: Monsoons help regulate temperatures, providing relief from the intense heat of the summer season.
Ecological balance: Monsoon rains are vital for maintaining the ecological balance in various ecosystems. They support biodiversity, replenish soil nutrients, and sustain flora and fauna.
Mechanism and origin of south west monsoon
Shifting of ITCZ (Inter-Tropical Convergence Zone. Northward shift of the ITCZ triggers the onset of Indian monsoon creating a low pressure area.
Summer Heating: As the northern hemisphere tilts towards the sun in June, intense solar heating creates a low-pressure zone over the Indian subcontinent. This draws moisture-laden winds, primarily from the southwest Indian Ocean, towards the low-pressure system.
Coriolis Effect: Earth’s rotation deflects these winds to the right, giving rise to the characteristic southwest monsoon winds. These winds carry large amounts of moisture, promising rain and relief to the parched land.
Orographic uplift: As monsoon winds encounter mountain ranges, they are forced to rise, leading to adiabatic cooling and condensation. This results in heavy rainfall on the windward side and rain shadow effect in leeward side.
Tibetan plateau: Tibetan plateau’s vast elevated expanse acts as a heat sink, further intensifying the low pressure system of India.
Jet streams: Upper level atmospheric currents, like the westerly jet stream, influence the direction and intensity of the monsoon winds.
Mechanism of retreating monsoon
Movement of sun: As the sun shifts southward in the autumn months, the high-pressure belt over the Tropic of Capricorn strengthens. This creates a pressure gradient between the landmass of India, which cools down after the monsoon, and the warm Indian Ocean.
Weakening of monsoon trough: Weakening and shifting of monsoon trough. This reduces the pressure difference between the land and sea, further weakening the southwest monsoon winds.
Wind pattern reversal: In Sept-Oct sun shines over tropic of Capricorn which results in the withdrawal of ITCZ to south. This alters the wind pattern over the Indian Ocean. Instead of the south-westerly winds of the Southwest Monsoon, north-easterly winds from the Bay of Bengal prevail.
Rainfall patterns: The retreating monsoon brings rainfall to parts of the east coast of India, particularly Tamil Nadu and Andhra Pradesh. This is known as the northeast monsoon or the winter monsoon.
October heat: The retreat of the monsoon is marked by clear skies and a rise in temperature. While day temperatures are high, nights are cool and pleasant. Owing to the conditions of high temperature and humidity, the weather becomes rather oppressive during the day. This is commonly known as 'October heat'.
Cyclonic depressions: During this season, cyclones and depressions in the Bay of Bengal can cause heavy rainfall.
Characteristic features of Indian Monsoons
Seasonal: Indian monsoon is a seasonal phenomenon, occurring from June to September. The seasonality of the Indian monsoon is driven by the differential heating of land and sea.
Topography and relief: The topography and relief features of India play a significant role in influencing the Indian monsoon. The Himalayas, Western Ghats, and Aravalli Range mountains act as barriers to the wind systems, affecting the distribution and intensity of rainfall.
Example: Western Ghats acting as a barrier for Arabian Sea branch and Bay of Bengal branch influenced by Himalayas.
Monsoon breaks: Monsoon breaks, also known as 'monsoon depressions' or 'monsoon mid-season breaks,' are periods of reduced rainfall during the Indian monsoon season.
Unequal distribution: Rainfall decreases as the distance form sea increases.
Example: Rainfall distribution of Kolkata> Patna> Allahabad
Onset and withdrawal: The onset of the southwest monsoon typically occurs in early June over the Kerala coast and advances northward and westward thereafter. It withdraws from northwest India by the end of September and from the rest of the country by mid-October.
Changing patterns Indian monsoons
Reduced rainfall: Studies have shown a decline in average monsoon rainfall over India in recent decades with some regions experiencing up to a 20% reduction in rainfall.
Increased variability: The monsoon has become more erratic and unpredictable, with periods of intense rainfall interspersed with prolonged dry spells.
Shifted onset and retreat: The onset and withdrawal of the monsoon have also shifted in recent years. The monsoon tends to arrive later and retreat earlier, shortening the overall monsoon season.
Changes in intensity: Studies suggest an increase in the intensity of rainfall during the monsoon season. This intensification can lead to more instances of heavy rainfall and flooding in certain regions.
Changes in cyclone patterns: The frequency and intensity of tropical cyclones in the Indian Ocean have increased.