and
Is there a connection? A study finds that high levels of aerosols in the atmosphere further worsen the impacts of El Nino on the rainfall leading to increased frequency of droughts in India.
I
ndia has a long history of droughts. There were 26 major droughts from 1870 to 2018, when the All India Summer Monsoon Rainfall (AISMR) was found to be lesser than the mean rainfall for the country. Even the most recent drought was disastrous for India, affecting agriculture and water resources across the country. Evidence shows that there has been a gradual increase in the frequency of droughts in the second half of the twentieth century as compared to the first half. A number of studies have attributed droughts in India to El Niño effects, which occur when there is abnormal warming over the Pacific Ocean, which has a negative impact on the monsoon, as it blocks the flow of
Environment & people
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March 2020
moisture-bearing winds from the oceans to the Indian landmass. However, a new study titled ‘Elevated aerosol layer over south Asia worsens the Indian droughts’ published in Nature Scientific Reports finds that presence of high levels of aerosols in the atmosphere further worsen the El Niño effect and have a role to play in declining rainfall patterns and increasing incidence of droughts in the country. What are aerosols? Aerosols are minute particles suspended in the atmosphere. Sufficiently large particles scatter and absorb sunlight, and reduce visibility (haze) and redden sunrises and sunsets. Aerosols interact both directly and indirectly with the Earth's radiation budget, which includes the balance between incoming solar radiation and outgoing radiation (that includes partly reflected solar radiation and partly radiation emitted from the Earth, including the atmosphere). A change in balance can cause the temperature of the atmosphere to increase or decrease and
affect the climate. The impact of aerosols on the Indian monsoon Aerosols lead to enhancement or suppression of the Indian summer monsoon rainfall depending on their duration and scale along with their tendency to scatter sunlight directly back into space, or by changing the size of cloud particles, thus negatively affecting their capacity to absorb sunlight. This leads to reduced temperatures over land, resulting in weaker land-sea temperature gradient, which is an essential force required to pull the monsoon circulation from ocean to land. Recent evidence shows that aerosols levels increase during the El Niño period. For example, this study found that an elevated layer of aerosol was present over South Asia during the months of JulyAugust of 2015 and 2016. However, this aerosol layer appeared thicker and was centered over the entire North Indian monsoon region during the El Niño period of
