Intensified occurrences of snow droughts are related to the snow cover dynamics in the Hindu Kush Himalayas

Identification of potential snow drought (SD) hotspots is critical, especially considering seasonal snow imbalances in the recent years, with snow being one of the significant water resource in the Hindu Kush Himalayas (HKH). The critical linkage between the spatio-temporal anomalies of snow cover days (SCD) and SD remains under-observed in the HKH region. To investigate this linkage, we identified the SD at basin (11 basins) using the snow water equivalent index (SWEI) based on the High Mountain Asia Snow Reanalysis (HMASR) data from 1999 to 2016 water cycle. The declined snow cover days (DSCD) and snow cover persistence anomalies (SCPA) at sub-km spatial resolution from 2002 to 2018 were estimated from the improved MOYDGL06 snow cover data, respectively. Our basin scale findings indicate moderate to severe snow droughts were observed in 2008, 2011, 2015 and 2016 in the North-West (NW), Amu-Darya (AD), Indus (IN), and Salween (SA) and Mekong (MK) basins with strong linkages to DSCD and SCPA. The observed frequencies of snow-droughts were 25, 16, 14, 5, and 3 in the NW, AD, IN, MK, SA basins, respectively. These basins also exhibit significant DSCD, approximately 12, 11, 12 in NW, AD, IN, respectively, and 14 days in MK and SA basins each. Further, it is noted that significantly higher negative SCPA coincides with the SD episodes in drought years. Both SD and DSCD were more prominent between 3000 and 6000 m elevations in the HKH, which are often considered under elevation dependent warming (EDW) scenarios in various studies. Overall, we observed that a higher frequency of drought events corresponds to a greater DSCD and higher negative magnitudes of SCPA. These insights indicate the urgent need for snow-conservation strategies and development and enforcement of strong policies.