PUNE: Not just El Nino, but air pollution may also be worsening droughts in the country, a new study has revealed.
An Indian Institute of Tropical Meteorology (IITM) study has revealed that during El Nino years, pollutants from south Asian countries can amplify the effect of the climate cycle on the monsoon, worsening an ongoing drought situation.
The study said severity of droughts during El Nino years was amplified by 17% due to changes in aerosol pollution (a cloud of solid or liquid particles). It said pollutant loading in the Asian Tropopause Aerosol Layer — a high altitude layer of pollutants — reduced the amount of solar radiation in the monsoon region, thereby aggravating the severity of drought by further weakening the monsoon circulation.
It said future increases in industrial emissions from both east and south Asia would lead to a wider and thicker pollutant aerosol layer in the upper troposphere, potentially amplifying the severity of droughts over India.
Suvarna Fadnavis, a chief researcher and IITM scientist, told TOI that the increase in industrial emissions from India and China added millions of metric tonnes of aerosols into the atmosphere. “In a global warming environment, the tropical Pacific is predicted to witness more frequent extreme El Nino events. Aerosol pollution loading over South Asia is still expected to remain large at least until the end of the 2040s. Thus, more extreme El Nino events, in the backdrop of the rising aerosol emission, will have an adverse impact on the severity of droughts over the monsoon region,” she said.
IITM researcher T P Sanin, also the co-author of this study, said El Nino itself led to a decrease in rain over India, with a monsoon rainfall suppressed by 2mm to 6mm per day. “Add to this the effect of aerosols, and the decrease in rainfall is around 17% over central India,” the study showed.
“We estimate that aerosol loading in 2009 and 2015 has induced a rainfall deficit of 1-7mm per day (14%) over central India. The combined effect of El Nino and the increased aerosol loading can led to a rainfall deficit of approximately 4-12 mm per day over India,” Fadnavis said.
“The abnormal cooling over north India and Tibetan plateau during monsoon is a consequence of the enhanced aerosol loading over the south Asian upper troposphere,” she said.
Other researchers involved in the study include Chaitri Roy from IITM; Matthew Rowlinson, Alexandru Rap from School of Earth and Environment, University of Leeds, Leeds, UK; Jean-Paul Vernier from National Institute of Aerospace, Hampton, Virginia, United States and Christopher E Sioris from the Air Quality Research Division, Environment and Climate Change, Toronto, Canada.