Monsoon rainfall Current Affairs - 2020

IMD: El Nino to be neutral; Normal Monsoon rains for India

On March 19, 2020, the Indian Meteorological Department announced that the El Nino Weather Phenomenon is to remain neutral this year between May and July. This will bring in normal rains to India during South West Monsoon.

The Indian Monsoon is greatly affected by the El Nino and La Nina Weather Phenomenon. The neutral event of the weather phenomenon is addressed as ENSO Oscillation.

ENSO Neutral: The Usual Weather System in the Pacific

The trade winds that flows from the east to west (from South America to Australia) pushes warm water from the off coast of South America towards Eastern Australia and Asia. The waters are warmed up as they are in the tropical zone of the earth receiving direct sun rays. The warm water rises the air and gives plentiful rainfall in the region of Australia and Asia.

Also, the piling up of warm water in the western Pacific in turn pushes the cold under ocean waters towards eastern side of the Pacific (towards South America). This is called upwelling. This makes the climate in the western coast of South America cool.

Monsoon and ENSO

The ENSO phenomenon strengthens the trade winds that give good rains to India during Monsoon. It is the trade winds that get deflected due to Corolis force and blow as south west monsoon.

The heating up of Himalayas during summer creates a low pressure in the region. This low pressure attracts the moist high-pressure winds in the equator. They are moist due to the ENSO phenomenon.

Therefore, India receives good rainfall when ENSO is neutral

What is El Nino?

During El Nino, the ocean waters in the western Pacific (near Australia) warms up. This breaks the warm waters from reaching the Australian coast. This is because, the oceanic temperature in the middle of the Pacific is greater than its coastal. Hence, water starts moving from Australian coast and South American Coast towards the centre of the ocean. Rainfall now occurs in this part of the ocean, making both the coasts dry. Hence, the trade winds reaching near Indian waters are dry as well. This weakens Indian Monsoon.

Western Ghats’ forests vital for monsoon rainfall in Tamil Nadu: Study

Researchers have found that dense vegetation in Western Ghats determines amount of rainfall that Tamil Nadu gets during the summer monsoon. The study highlights importance of urgent need to stop deforestation in the Western Ghats.

Key Highlights of Study

Researchers had used models to compare contribution of Western Ghats with and without forest cover to study role of vegetation cover in Western Ghats in supplying moisture to southwest monsoon rainfall. They had selected three years (1993, 1999 and 2002) for their study when Tamil Nadu had experienced extreme deficit in summer monsoon rainfall.

The study found that dense forests of Western Ghats contribute as much as 40% of moisture to southwest monsoon rainfall over Tamil Nadu during normal monsoon years. The average contribution is 25-30%, but during monsoon deficit years, contribution increases to as high as 50%.

The forests of Western Ghats contribute as much as 3 mm per day of rainfall during August and September over majority of locations in Tamil Nadu and 1 mm per day during June and July. But when vegetation cover is removed from Western Ghats, there is significant drop in rainfall in range of 1-2.5 mm per day. This translates to average of 25% of total monsoon rainfall over Tamil Nadu.

The deforestation of forests in Western Ghats has led to 0.25 degree C increase in surface temperature across state. It has reduced rainfall over the State by 40-50% during all three years. If there is no vegetation in Ghats then Tamil Nadu will be severely impacted especially during the monsoon-deficit years. The study shows that Western Ghats acts as capacitor and forest land and vegetation gets recharged with water during wet spell and during break periods moisture is released and which contributes to rainfall to state.