FAVOURABLE CONDITIONS FOR SOUTHWEST MONSOON

Focus: GS-I Geography

Why in news?

Conditions are becoming favourable for further advancement of Southwest Monsoon into some more parts of Central Arabian Sea.

Monsoon

• Monsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea.
• Usually, the term monsoon is used to refer to the rainy phase of a seasonally changing pattern, although technically there is also a dry phase.
• The term is sometimes incorrectly used for locally heavy but short-term rains.
• India’s geography and geology are climatically pivotal: the Thar Desert in the northwest and the Himalayas in the north work in tandem to create a culturally and economically important monsoonal regime.
• As in much of the tropics, monsoonal and other weather patterns in India can be wildly unstable: epochal droughts, floods, cyclones, and other natural disasters are sporadic, but have displaced or ended millions of human lives.

Formation of Southwest monsoon rains

1. The Thar Desert and adjoining areas of the northern and central Indian subcontinent heat up considerably during the hot summers.
2. This causes a low-pressure area over the northern and central Indian subcontinent.
3. To fill this void, the moisture-laden winds from the Indian Ocean rush into the subcontinent.
4. These winds, rich in moisture, are drawn towards the Himalayas.
5. The Himalayas act like a high wall, blocking the winds from passing into Central Asia, and forcing them to rise.
6. As the clouds rise, their temperature drops, and precipitation occurs.

Branches of Southwest monsoon winds

The moisture-laden winds on reaching the southernmost point of the Indian Peninsula, due to its topography, become divided into two parts: the Arabian Sea Branch and the Bay of Bengal Branch.

1. The Arabian Sea Branch of the Southwest Monsoon first hits the Western Ghats of the coastal state of Kerala.

This makes Kerala the first state in India to receive rain from the Southwest Monsoon.

2. The Bay of Bengal Branch of Southwest Monsoon flows over the Bay of Bengal heading towards North-East India and Bengal, picking up more moisture from the Bay of Bengal.

The winds arrive at the Eastern Himalayas with large amounts of rain.

This makes Meghalaya one of the wettest places on Earth.

Southwest Monsoon season

• The period June to September is referred to as the ‘Southwest Monsoon’ period which is the principal rainy season for the Indian subcontinent.
• The whole country receives nearly 75% of its rainfall during this period. 
• The total annual rainfall is maximum over the southernmost part of the state.

Note: Tamil Nadu is considered as a rain shadow region as it lies on the eastern (leaward side) side of western ghats.