Surge in Pollution Threatens Monsoon Rainfall According to Research

The results were striking; as aerosol levels escalated from clean to heavily polluted, there was a marked reduction in the number of convective rain-producing elements within a cloud cluster.

14 June 2024

By Ishika Kumar

PUNE: A study conducted by researchers at the Indian Institute of Tropical Meteorology (IITM) in Pune has unveiled a pressing environmental concern: increasing pollution levels could significantly diminish rainfall during India’s crucial monsoon season. 

Published in the Journal of Atmospheric and Solar-Terrestrial Physics, the study presents compelling evidence that aerosol concentrations, primarily from industrial emissions and other anthropogenic activities, could drastically alter rainfall patterns.

Analysing Monsoon Cloud Clusters

The research delved into the lifecycle of a notable rain cloud cluster that formed over the Indian peninsula in the early summer monsoon of 2018, under dry mid-tropospheric conditions. Utilising state-of-the-art numerical simulations, the scientists explored how varying aerosol levels impacted the development and precipitation of these clouds. The results were striking; as aerosol levels escalated from clean to heavily polluted, there was a marked reduction in the number of convective rain-producing elements within the cloud cluster.

Impact on Rainfall Production

Dr Thara V Prabhakaran, a senior scientist at IITM, highlighted a significant decrease in convective elements within the cloud cluster as aerosol concentrations increased. “The area covered by intense rainfall types like isolated thunderstorms shrank considerably in more polluted scenarios,” she explained. According to Dr Prabhakaran, the study observed a 30% reduction in convective elements in moderately polluted cases and over a 50% reduction in heavily polluted scenarios compared to clean conditions.

Soumya Samanta, the study’s lead author, explained the microphysical mechanisms behind these findings. Higher aerosol levels led to the formation of smaller cloud droplets, which initially increased total cloud water through condensation. However, these smaller droplets were less effective in producing heavier rainfall. Additionally, dry mid-level atmospheric conditions further suppressed cloud growth and rainfall production, significantly declining overall precipitation.

Broader Implications of the Study

The research finds the profound impact of aerosols on monsoon rainfall patterns. Aerosols, which originate from various natural and anthropogenic sources, including dust, sea salt, volcanic eruptions, wildfires, industrial processes, vehicle emissions and fossil fuel combustion, play a critical role in cloud formation. 

However, when aerosol levels rise unchecked, they disrupt the microphysical processes essential for heavy rainfall, leading to a substantial reduction in monsoon precipitation.

One particularly interesting finding of the study was the increased evaporation rates of cloud droplets as aerosol levels rose. This increase is likely due to the formation of a larger number of smaller cloud droplets, which collectively have a greater total surface area exposed to evaporation.

Environmental and Economic Consequences

The study’s implications extend beyond meteorology, highlighting significant threats to India’s monsoon-dependent agricultural economy and water resources. The monsoon season is vital for replenishing water supplies and sustaining agriculture nationwide. A decline in monsoon rainfall could devastate crop yields, water availability and overall economic stability.

Urgent Need for Mitigation

The findings of this study prompt the urgent need for stringent environmental regulations and effective mitigation strategies to curb aerosol emissions. Policymakers, industries and communities must collaborate to reduce pollution levels and protect the integrity of the monsoon season. Implementing measures to control industrial emissions, promote cleaner transportation and reduce the burning of fossil fuels can play a crucial role in preserving rainfall patterns and ensuring water security.

As India confronts escalating environmental challenges, the IITM study serves as a critical reminder of the intricate link between human activities and natural phenomena like the monsoon. Addressing these issues requires concerted efforts to mitigate pollution and safeguard the sustainability of India’s vital monsoon season. 

The study by IITM researchers presents a clear danger: if pollution levels continue to rise unchecked, the country could face severe disruptions in rainfall patterns, leading to water scarcity amid already existing water shortage in certain areas, and with far-reaching consequences for agriculture, water resources and overall economic health.