The decline in western disturbance activity over Northern India in recent decades

Western disturbances (WDs) are upper-tropospheric synoptic-scale cyclonic storms that travel eastwards embedded in the subtropical westerly jet stream. They are of veritable significance to the sustenance of the population in the north and northwest regions of the Indian subcontinent and are often harbingers of extreme precipitation events during the boreal winter. This study utilizes a tracking algorithm with the upper-level vorticity field of the ERA5 reanalysis product to catalog events over the northern part of the Indian subcontinent for 39 WD seasons (Nov–Mar; 1980–2019), including information about their trajectory and precipitation. The contribution of WDs to the region’s total precipitation has been quantified comprehensively, enabling the proposition of a “core WD zone” and an intensity categorization of WDs affecting India. The core zone exhibits a decreasing trend for annual WD-associated precipitation despite the frequency of storms depicting no evident trend. The combined mean frequency of strong and extreme WDs declined by as much as ~ 43%, contrary to the mean occurrences of feeble and moderate WDs, which rose by ~ 11%. However, the mean seasonal precipitation volume decreased for all the categories, irrespective of the changes in their frequencies. The sharpest decline (~ 49%) was observed for the most intense WDs (strong and extreme), primarily explaining the decreasing WD precipitation intensity across the core WD zone. The spatial distribution and evolution of various dynamical parameters reveal an inhibitive dynamic state of the atmosphere restricting the moisture advection capacity of WDs and the resultant decline in the associated precipitation over the core WD zone in recent decades.