Aerosols increase drought severity over the Indian subcontinent

Education, Engineering, Science, Research,

Pune, September 10 2019: 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 per cent during El Nino years.

The team led by Dr.Suvarna S.
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 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 produces an 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 Nino 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 Nino 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 T.P.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.

By Abhay S.D. Rajput

(India Science Wire)

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