Evolving Characteristics in Western Disturbances over the Hindu Kush Himalayas

Western Disturbances (WD) are key atmospheric phenomena over northern India, Pakistan, and the Western Himalayas, especially during winter months (December to February). In recent years, increasing variability in these systems has been observed across all seasons, notably pre-monsoonal months (March to May), although thorough investigation remains underexplored. The study evaluates the shifting behaviour and structure in WDs across two climatologically distinct periods – 1950 to 1976 and 1977 to 2022, corresponding to the well-documented 1976-1977 climate shift. In this study, vorticity-based WD track data, coupled with the ERA5 reanalysis dataset, have been utilised to analyse the shift. Behavioural changes are quantified through frequency trends, maximum vorticity distribution and mean track, while structural evolution is examined through composite vertical profiles of key atmospheric variables.  The study unravels notable increase in WD frequency during the pre-monsoon season in recent decades, accompanied by a westward shift in WD origins and longer track durations, thereby enhancing the potential for moisture transport. Furthermore, substantial strengthening of upper-level zonal winds, intensified mid-tropospheric convection, and atmospheric moisture availability have been observed through structural analysis. Such transformations indicate a transition of WD towards hybrid systems with enhanced convective features, thereby elevating the potential for extreme precipitation events during the pre-monsoon period. This improved understanding of the evolving WD dynamics is critical for hydrological planning, climate action, strategies and disaster preparedness in the highly vulnerable Himalayan and adjoining regions.