India: Air pollution and Assam floods
By Farhana Ahmed
The North-eastern Indian state of Assam is naturally the most flood-prone state of the country as the monsoon winds blowing from Bay of Bengal hits the sub-Himalayan hills of Arunachal Pradesh to its north lashing the plains with heavy precipitation during the summer. According to the Rastriya Barh Ayog (RBA)—the National Flood Commission, 31.05 lakh hectares of the total 78.523 lakh hectares area of the state is prone to frequent floods. Secondly, the Brahmaputra—the lifeline of the state originates from a glacier at Tibet that carry additional amount of water due to snow-melt in the summer makes the entire valley flooded. There are reasons for the annual havoc of flood and river bank erosion affecting Assam annually, but one more phenomenon has been troubling the region. This is the increasing air pollution felt in the area in last few years.
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Research conducted by Indian Institute of Technology (IIT), Kanpur found a link between air pollution and intense rainfall recently. Analysing long-term satellite data between 2002 and 2016 and modelling to understand the association between aerosols and cloud properties, the study found that air pollution particles lead to change in the physical properties of monsoon clouds, which can lead to more intense rainfall, flash floods and unusual gaps in the progression of monsoon rainfall. “Not all extreme rain events can be linked to aerosols as other meteorological factors also play a role, but cases of extreme and erratic monsoon rainfall in inland areas affected by air pollution may be linked to this phenomenon,” says the study.
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Air pollution can affects health and the World Health Organization estimates that it caused 3.7 million premature deaths worldwide in 2012 alone. But now another recent study shows that air pollution can trigger floods as well. In July 2013, heavy rainfall resulted in a catastrophic flood in Sichuan Basin, a mountainous area of China. Nearly 2.5 feet of rain fell in just five days which led to the findings that air quality played a role in the valley’s disaster. It was found that in some geographic regions, aerosols absorb heat from the sun, suppressing the chance of rain during the day and stabilizing the atmosphere. At night the warmed, rising air is transported to mountainous areas before it heads higher up into the atmosphere. This causes massive precipitation that can actually make flooding worse.
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The studies on atmospheric simulations in Sichuan Basin show that if current industrial emissions are reduced to a level before the China’s economic boom, less precipitation (up to 60% lower) could be predicted. This is due to weakening of the “aerosol-enhanced conditional instability” mechanism. This suggests that air pollutants reduction can effectively mitigated floods in that area. This discovery is also called “aerosol-enhanced conditional instability,” and its flipside is that reducing pollution in places like Sichuan can actually reduce floods. As pollution particles worsen flooding, it could help future weather forecasters predict floods.
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