Changes in western disturbances over the Western Himalayas in a warming environment

The climate of the Western-Himalayan (WH) region is sensitively dependent on precipitation during the winter and early spring months (December-to-April, DJFMA) produced largely by synoptic weather-systems known as Western Disturbances (WD), which originate from the Mediterranean region and propagate eastward as troughs and cyclonic lows embedded in the sub-tropical westerlies. While the WH region has witnessed a significant rise in surface temperatures since the post-1950s, there are no major trends in the DJFMA seasonal precipitation. Past studies, based on station observations from the WH, have reported a significant increase in the occurrence of extreme precipitation events in recent decades. Here, we have analyzed multi-source climate datasets to understand the increasing frequency of heavy precipitation events over WH. Our analysis suggests that pronounced warming trends over the Tibetan Plateau in recent decades, arising due to the elevation dependency of the climatic warming signal, have favored enhancement of meridional temperature gradients at middle and upper-tropospheric levels over the sub-tropics and mid-latitudes. The present findings indicate that the observed pattern of mid-tropospheric warming trend in recent decades over west-central Asia has led to increased baroclinic instability of the mean westerly winds, thereby favoring increased variability of WDs and higher propensity of heavy precipitation events over the WH.