BSS . Dhaka | 5 april 2014:
South Asia A new study by US and Indian scientists say desert dust originating in West Asia increases or reduces the intensity of the South Asian monsoon.
The article published in Nature Geoscience, this week, tried to explain how aerosols — fine particles or liquid droplets in the air — influenced rainfall patterns in unanticipated ways, with minor changes in one location quickly affecting weather patterns thousands of miles away.
“A number of studies have focused on the role of humanly produced aerosols like soot, which absorbs sunlight leading to a warming and sulphate, which reflects sunlight back to space leading to a cooling, on the monsoon. These aerosols are products of pollution from fossil fuel use, cooking and agricultural burning,” said Philip J Rasch, chief scientist for the Climate Science at the Pacific Northwest National Laboratory and a co-author of the new paper.
Their analysis is that by increasing the heat in the atmosphere, dust particles cause winds over North Africa and the Arabian Peninsula to blow eastwards towards South Asia that results in rain or drought within a week.
Monsoon is the lifeline for South Asia. “Even slight changes — plus or minus 10% — in the rainfall from the average long term pattern can mean either flood or drought, spelling disaster for the whole of South Asia. Therefore it is very important that all factors that influence the strength of monsoon or drought be understood,” another author V Vinoj, assistant professor at the Indian Institute of Technology (IIT), Bhubaneswar said.
There is little understanding of how aerosols influence the monsoon on a global scale. “This uncertainty is due to its several complicated pathways through which it affects climate,” Vinoj explained.
“On a regional scale such uncertainties become even more critical,” he added.
Dust plays a more important role than aerosols produced by humans, such as soot, because there is far more of it according to Professor J Srinivasan, chairperson of the Divecha Centre for Climate Change at IISc.
If soot particles get deposited on dust then it will enhance the influence of dust, he said. Previous studies have also largely focused on local impacts of aerosols over a longer period of time.
“For example, most studies have explored how aerosols emissions that started in the spring might influence rainfall in the summertime,” Rasch said.
“The new study, instead, probed rapid effects of natural aerosol changes on climate quite far away”, he added.
Most weather forecast models have not taken the influence of dust into account until recently, Srinivasan said. “If weather forecast models include dust their short term forecast of rainfall will improve.”
Scientists from the Indian Institute of Technology (IIT) Bhubaneswar, and the Pacific Northwest National Laboratory in the US, used satellite data and analyzed global climate model simulations for this study.