A study of Himalayan extreme rainfall events using WRF-Chem

Abstract

The rising number of extreme rainfall events over the Himalayan foothill states of India during the recent decades has become a serious issue with the growing concern of aerosol influences. This study intends to provide some insight into aerosol and gas chemistry responses to changes in monsoon circulation and precipitation, and also assess the impact of aerosols on two recent infamous heavy rainfall events using coupled meteorology–chemistry–aerosol (WRF-Chem) model simulations. The sensitivity of aerosols and chemistry on rainfall distribution and the amount is evaluated using the simulations with and without chemistry. Results from this study show that the magnitude and spatial distribution of precipitation are significantly influenced by including aerosol and gas chemistry in the model simulations. Realistic meteorological conditions as well as rainfall amount and distribution are reproduced when aerosols and gasses are taken into account in the simulation. There is an overall enhancement of total cumulative rainfall as high as 20% due to aerosols and gas chemistry over the western Himalayan Indian states. This study shows that cloud-microphysical properties and the resulting precipitation distribution depend critically on the aerosol types and their concentrations under similar thermodynamic conditions. This study highlights the role of aerosol and gas chemistry and recognizes the importance of atmospheric chemistry in the model simulation for the analysis of Himalayan extreme precipitation events, and its further associations with the Himalayan hydrology.