Aerosols increase drought severity over the Indian subcontinent

A study has found that the El Nino effect further weakens the monsoon by transporting aerosols from the lower altitudes in East Asian region up and into the higher altitudes forming an aerosol layer over the South Asian region. This remains hanging over there during monsoon

Aerosols increase drought severity over the Indian subcontinent

Abhay SD Rajput (India Science Wire)

A team of atmospheric scientists from India, USA and Canada have found that aerosols in the atmosphere can increase the severity of droughts over the Indian subcontinent by as much as 17% during El Nino years.

The team led by Dr Suvarna Fadnavis of the Indian Institute of Tropical Meteorology (IITM), Pune has reported this in a new study published in Scientific Reports.

The El Nino phenomenon -- which occurs when there is abnormal warming over the Pacific Ocean – is already considered as a deterrent for the Indian monsoon on the ground that it blocks the flow of moisture-bearing winds from the oceans to the Indian landmass.

The new study has found that it further weakens the monsoon by transporting aerosols from the lower altitudes in East Asian region up and into the higher altitudes (12-18 km) forming an aerosol layer called Asian Tropopause Aerosol Layer (ATAL) over South Asian region. It remains hanging over there during monsoon. The thickening of this aerosol layer results in the reduction in the amount of solar energy reaching the earth thus weakening the monsoon circulation and increasing the severity of drought conditions.

"The El Niño itself leads to a decrease in rainfall over India and the inclusion of aerosols further amplifies this decrease. Our study reveals that the combined effect of El Nino and aerosols produce aggravated subsidence in rainfall over the Indian region compared to the individual effect of El Niño. By using satellite observations and a series of model simulations, we found that the severity of droughts during El Niño years over the Indian subcontinent is amplified by 17%," said Dr Fadnavis.

Noting that in recent decades there has been an increase in the frequency of El Niño events and the frequency of droughts over India, the researchers warned against any further increase in industrial emissions and thus aerosols from both East and South Asia. It can lead to a wider and thicker aerosol layer in the upper troposphere and potentially further, amplify the severity of droughts.

"When India is already vulnerable to hydrological and weather extremes, the combined effect of El Niño and aerosols in increasing drought severity will only subject India to more hydrological stress, while affecting agriculture and the livelihood of millions of people. Reducing aerosol emissions is not only essential for improving air quality, but also for reducing drought conditions and avoiding negative consequences for millions of people living in the Indian subcontinent," Dr Fadvanis added.

Besides Dr Fadnavis, the study team included TP Sabin and Chaitri Roy of Indian Institute of Tropical Meteorology, Mathew Rowlinson and Alexandru Rap of School of Earth and Environment, University of Leeds, UK, Jean-Paul Vernier of National Institute of Aerospace, and NASA Langley Research Center, Virginia, USA, and Christopher E Sioris of Air Quality Research Division, Environment and Climate Change, Toronto, Canada.

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