Changing characteristics of Western Disturbances precipitation over Western Himalayas 

The Indian subcontinent experiences winter precipitation (December, January, and February) due to Western Disturbances (WDs), which are synoptic scale weather systems embedded in subtropical westerly jets (SWJs) at upper tropospheric levels. For Himalayan rivers, WDs precipitation is crucial for hydrological budget as it causes heavy precipitation, flooding, and snowfall. The precipitation caused by WDs is beneficial for agricultural activities such as sowing of wheat crop, barley etc. WDs and NON-WDs precipitation are classified into active and break phase. Active and break peaks of WDs and NON-WDs are computed based on the maximum precipitation occurring in each WDs and NON-WDs days. This study, highlights the changes in precipitation climatology of active WDs and NON-WDs during 1987-2020 using hourly ERA5 reanalysis dataset. Various statistical techniques such as Theil-Sen slope test is used to calculate the trend and to investigate the decline in frequency of active WDs precipitation. Further, the structure, dynamics, and moisture availability associated with changing WDs and NON-WDs are also examined in this work.  It has been observed that some characteristics of WDs have changed in the recent decade due to climate change. This is associated with decrease in active WDs precipitation but the precipitation amount is increasing in the recent years. Active WDs precipitation pattern has primarily been shifted towards the months of January and February. The dynamics showed that active NON-WDs days derive moisture from Bay of Bengal region which is due to ‘Ω shape’ amalgamated structure and ‘∞ shape’ wind formation leading to precipitation forming mechanism over Western Himalayas. This study helps in insightful understanding of WDs and NON-WDs precipitation during the recent years which is necessary to improve headwater storage policies and meet agricultural demands.