SYLLABUS

GS-1: Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc., geographical features and their location- changes in critical geographical features (including waterbodies and ice-caps) and in flora and fauna and the effects of such changes.

Context: India’s 2026 Southwest Monsoon ended with 759.4 mm of rainfall, 12.6% below the normal 868.6 mm, making it the country’s driest monsoon since 2015, while East and Northeast India recorded their driest monsoon since 1901.

About the Monsoon 

• The term monsoon originates from the Arabic word Mausim, meaning “season”. It refers to the seasonal reversal of winds, primarily caused by differential heating of land and sea and associated changes in atmospheric pressure.

• India experiences two major monsoon systems:

• Southwest Monsoon: June–September; the main rainy season.
• Northeast Monsoon: October–December; particularly important for southeastern and southern India.

Types of Monsoon

• Southwest Monsoon: Moisture-bearing southwesterly winds enter India through two major branches—the Arabian Sea branch and the Bay of Bengal branch. 

• The Arabian Sea branch produces heavy rainfall along the Western Ghats, while the Bay of Bengal branch moves towards eastern, northeastern and northern India. 
• The Southwest Monsoon normally reaches Kerala around 1 June and advances northwards in stages, generally covering the country by early July.

• Northeast Monsoon: During October–December, the Southwest Monsoon withdraws and winds reverse direction. 

• The northeast winds pick up moisture from the Bay of Bengal and bring significant rainfall to Tamil Nadu, coastal Andhra Pradesh and parts of the southern peninsula.

Major Factors Affecting the Indian Monsoon

• Inter-Tropical Convergence Zone (ITCZ): The ITCZ is a belt of low pressure and rising air where trade winds converge. 

• Its northward movement during summer helps establish the monsoon circulation, while its southward movement contributes to monsoon withdrawal.

• El Niño–Southern Oscillation (ENSO): El Niño, involving abnormal warming of the central and eastern tropical Pacific, is generally associated with a weaker Indian summer monsoon, while La Niña often supports stronger rainfall. 

• ENSO is one of the major controls of year-to-year monsoon variability.

• Indian Ocean Dipole (IOD): IOD refers to differences in sea-surface temperatures between the western and eastern Indian Ocean. 

• Along with ENSO, it is a major factor influencing interannual variations in Southwest Monsoon rainfall.

• Madden–Julian Oscillation (MJO): MJO is a tropical atmosphere–ocean phenomenon with a typical 30–60-day cycle. 

• Its eastward-moving convection influences the active and break phases of the Indian monsoon and is important for extended-range forecasting.

• Somali Jet: The Somali Jet is a strong cross-equatorial low-level flow that enters the Arabian Sea and reaches India during summer. 

• Its strengthening supports stronger monsoon conditions, particularly over peninsular India.

• Mascarene High: The Mascarene High is a high-pressure system over the southern Indian Ocean. 

• It facilitates cross-equatorial flow towards India, while variations in its intensity can produce monsoon surges and influence heavy rainfall along the west coast.

• Tropical Easterly Jet (TEJ): The Tropical Easterly Jet develops during the summer monsoon in the upper troposphere. 

• Its location and movement influence the pattern of monsoon rainfall over India.

• Monsoon Trough: It is an elongated low-pressure zone extending from the heat low over Pakistan towards the Bay of Bengal. 

• A southward shift generally produces active monsoon conditions, whereas a northward shift towards the Himalayan foothills can create a break phase over much of India.

Significance of Monsoon for India

• Agricultural Dependence: Nearly 64% of Indians depend on agriculture, while only about 55% of India’s net sown area is irrigated, making a large part of farming dependent on the Southwest Monsoon.

• Economic Growth: A good monsoon increases agricultural production, GDP growth, rural incomes and consumption, thereby supporting the broader economy.

• Crop Diversity: Regional variations in monsoon rainfall and generally favourable temperatures enable the cultivation of a wide variety of crops across India.

• Floods, Droughts and Soil Degradation: Uneven, delayed or intense rainfall can cause floods, droughts and soil erosion, affecting crop production, rural incomes and land fertility.

• Regional Life and Rabi Crops: Winter rainfall from Western Disturbances supports wheat and other rabi crops in northern India, while monsoon-shaped climatic conditions influence food habits, clothing and housing patterns across regions.