Deciphering Characteristics, Variability, and Drivers of Summer Monsoon Precipitation and Extremes over the Western Himalayas

Understanding the dynamics of precipitation in the western Himalayas (WH) during the Indian Summer Monsoon (ISM) is vital for societal well-being and effective disaster management. The region's complex terrain, diverse meteorological conditions, and observational uncertainties pose significant challenges in comprehending precipitation disparities and predicting extreme precipitation events (EPEs) across the WH. The present study provides a comprehensive investigation into the characteristics, drivers, and variability of summer monsoon precipitation, with a focus on EPEs and their underlying mechanisms in the WH. The findings reveal that EPEs, over the WH, defined as precipitation exceeding the 99^th percentile, are influenced by both large-scale (61%) and convective precipitation (39%). Monsoon depressions contribute to 25.49% of these events. Atmospheric patterns such as upper-tropospheric gyres, zonal waves, and omega-type blocking emerge as key precursors, facilitating the southward extension of moisture-laden winds and enhancing low-level moisture convergence. The tropical-extratropical interactions, including the shifting of the Intertropical Convergence Zone and baroclinic wave activity characterized by zonal wave numbers 5 and 8, play a crucial role in intensifying EPE. Furthermore, High-resolution simulation using WRF demonstrate improved representation of spatiotemporal precipitation patterns, interannual variability, and EPEs compared to observational datasets. Overall, this study provides valuable scientific insights into the complex interactions governing precipitation extremes in the Himalayas. The findings enhance the understanding of ISM precipitation variability and improve the ability to predict and mitigate the impacts of extreme events in the region.

Keywords: Western Himalayas, Indian Summer Monsoon, Extreme Precipitation Events, Physical Drivers