Is rainfall linked to pollution? Depends on whether you live north or south of Vindhyas

DTE analyses PM10 spatial data for August 2022 and 2023 

By Pulaha Roy
Published: Wednesday 04 October 2023
Photo: iStock

India has relatively good air quality during the monsoon months compared to other seasons because rainfall aids in the dispersion of pollutants such as particulate matter (PM)10 and 2.5.

But the correlation between more rainfall and better air quality is not that straightforward. Rather, analysis of PM10 spatial data by Down To Earth suggested the correlation depends on where one is residing in the country — north or south of the Vindhya mountains. 

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August 2023 was the driest month ever recorded by the India Meteorological Department, with a deficit of 36 per cent when compared to the long term average of 1971-2020. In 2022, cumulative rainfall was three per cent above the long term average. 

So, by that logic, August 2023 should have been the most polluted August ever. 

But, as seen in the graphic, the two maps highlight the spatial anomaly that exists when it comes to pollution. 

In both years, irrespective of the rainfall departures, whether positive or negative, peninsular India enjoyed comparatively lesser pollution levels compared to its northern counterpart. This anomaly is due to the fact that pollution depends on wind direction and speed, apart from other geographical considerations. 

So, is there any correlation between rainfall and pollution? A granular analysis of the rainfall data when correlated with pollution data establishes that in 2023, the northwestern part of the country had a deficit of 37 per cent. This deficit is manifested through higher pollution levels around Delhi and western region of Uttar Pradesh. 

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In 2022, eastern and north eastern states had a deficit of 27 per cent, which was reflected through higher pollution levels across West Bengal and Bihar.  

Indo-Gangetic Plains are always more vulnerable to higher pollution levels compared to the southern peninsula due to the Himalayas acting as a natural barrier by trapping pollutants.

While the pollution menace is a year-long phenomenon in India, it usually peaks at the onset of winter, which further coincides with the harvesting season across the country. 

But while farm stubble burning is a country-wide affair, farmers in Punjab and Haryana have come under the cosh due to emissions from the stubble clearance, adding more pollution to the existing levels across the Indo-Gangetic Plains. 

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