Air pollution could hit monsoon rains by as much as 15%

Nagpur: While monsoon is considered the cleanest season, with relatively low air pollution, experts say air pollution is likely to reduce the southwest monsoon rainfall by 10%-15% for the entire country.
A latest analysis by Climate Trends highlights the adverse impact of air pollution on performance of monsoon in India. The analysis states that as the pollution peaks in the coming years, monsoon rains may reduce by at least 10% or even more, say scientists. “Some places might even see rains reduced by as much as 50%. While there has been consensus across the scientific community that the rising air pollution levels would decrease rainfall substantially in the coming years, it might also result in unstable monsoon patterns. For instance, we might see extreme weather events like severe hailstorms, torrential rains along with an increase in the number of dry days, especially over places which are more polluted,” the analysis states.
As per the experts, air pollution is the result of suspended particles or aerosols in the atmosphere from anthropogenic emitting sources along with natural dust. “It would also impact the dynamics of monsoon, for instance delay in onset. Air pollution does not allow the landmass to warm up to the required levels. Due to the presence of pollutants, heating of land takes place at a slower rate,” says Dilip Ganguly, associate professor at the Centre for Atmospheric Sciences, Indian Institute of Technology (IIT) Delhi.
Stating that strong latitudinal and vertical gradient in aerosols would lead to gradual reduction in southwest monsoon mean rainfall, SN Tripathi, head of the department of civil engineering at IIT Kanpur says, “The most affected places would be areas with more pollution levels. It is very non-linear, as it is the result of an interplay between meteorology and aerosols. The southwest monsoon is driven by the difference between land temperatures and ocean temperatures. Presence of large scale aerosols over the Indian landmass would lead to dimming of the land surface. The entire process would lead to weakening of the dynamics of monsoon, which might even include delay in onset of monsoon.”
Tripathi is also steering committee member of the National Clean Air Programme (NCAP).
The analysis further adds that though air pollution is impacting rainfall in the country, the Indo-Gangetic plains seem to be in a tight spot. “From March to May, the land surface gets heated, due to which the strength of the inversion layer reduces, bringing down the pollution levels. However, during that time, dust from western Rajasthan and the adjoining desert region of Pakistan starts transporting over the Indo-Gangetic plains. This, along with local emissions, leads to an increase in summertime pollution. Also, the geography of the north-western plains including Delhi-NCR is also not supportive. The entire Himalayan region guards the Indo-Gangetic plains, which does not allow pollutants to escape and acts as a barrier,” says Krishnan Raghavan, scientist at the Indian Institute of Tropical Meteorology, and lead author on Intergovernmental Panel on Climate Change (IPCC) Working Group 1 report.
RAIN, RAIN GOES AWAY
- Air pollution likely to decrease southwest monsoon rainfall by 10%-15% for the country
- Some places might see rains reduced by as much as 50%
- Might witness extreme weather events like severe hailstorms, torrential rains along with increase in number of dry days
- Most affected places would be areas with more pollution levels
- Pollutants remain trapped in Indo-Gangetic plains