Impacts of anthropogenic emissions on monsoon precipitation over western India: Insights from high-resolution regional modeling

Air quality and climate over the western Indian region have been shown to be strongly influenced by trans-regional anthropogenic emissions originated from the Indo-Gangetic Plain (IGP) and central India, besides the local and regional processes. Nevertheless, the relative roles of local versus remote anthropogenic processes in changing precipitation over western India have remained unclear. In this regard, numerical simulations have been conducted using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to quantify regional versus trans-regional anthropogenic effects on cloud droplet number concentration (CDNC) and precipitation during monsoon (August 2019). WRF-Chem simulations show a good agreement with the ERA5 reanalysis for cloud fraction (CF) (r = 0.88, MB = 0.08 mm/day) and accumulated monthly precipitation (AMP) (r = 0.84, MB = -0.14 mm/day). Sensitivity simulations reveal that regional plus trans-regional anthropogenic emissions enhance CDNC by up to 5.1×10⁶ number/cm² (~121% of the average CDNC over WI) but significantly reduce the precipitation by up to 45 mm (~15% of the average precipitation). The findings also revealed that the impact of trans-regional emissions in perturbing CDNC and precipitation is higher than that of regional emissions. Our results suggest that anthropogenic emissions can substantially lower water resources in this already stressed arid region in India. The study also highlights that policies need to aim emission reductions ubiquitously and not only over western India for mitigating pollution impacts on regional precipitation.