Characteristic Changes in the Strengthening Western Disturbances over Karakoram in Recent Decades

Abstract

Western disturbances (WDs) are upper-tropospheric mid-latitude synoptic systems propagating eastward along the subtropical westerly jet stream. They are capable of causing extreme precipitation events and have strengthened their impact over the Karakoram part of the Himalayas in recent decades. They play a crucial role in the sustenance of the “Karakoram Anomaly,” which refers to the anomalous stability/surge of a few Karakoram glaciers in contrast to the other glaciers of the Himalayas. Using the existing WD-catalog derived from ERA5 and MERRA2 reanalysis datasets, we observed that the core genesis zone for Karakoram WDs had undergone a statistically significant shift of ~ 9.7^oE, migrating towards more favourable conditions for cyclogenesis. The study proposes a new parameter to identify regions of potential extratropical cyclogenesis. The shift can be attributed to an enhanced genesis potential, convergence, and higher moisture availability along the WD path. Composite analysis suggests that moisture availability has risen significantly over the shifted zone. Moreover, the propagation speeds of these systems have significantly declined, which explains the recent intensification of precipitation events related to WDs over the Karakoram and hints toward a crucial synoptic influence on the anomalous regional mass-balance phenomenon.