Flash Snow Drought: Escalating Risks to Mountain Water Resources at local scale

Snow plays a critical role in water resources, the planetary energy balance, glacier nourishment, ecosystem and the winter tourism economy. In recent decades, rising temperatures have led to a decline in snowfall and shifting of patterns. These changes have resulted in reduced snowpack and earlier snowmelt, thereby triggering snow drought conditions. Since the first formal definition of snow drought in 2017, the topic has gained increasing scientific attention, with the first systematic studies published in 2019, followed by significant advancements in subsequent years. However, flash snow droughts (FsD) have not yet been studied and remain unexamined. FsD are short-duration events characterized by rapid onset and intensification, occurring over timescales ranging from weeks to month. These events may arise due to low precipitation accompanied by warm winter. Consequently, establishing a clear definition and identifying FsD hotspots are critical, particularly in regions experiencing imbalanced seasonal snow patterns and low snowpack. In this work, we examine FsD at a 500 m spatial resolution in the North-West Basin part of Afghanistan of the Hindu Kush Himalaya (HKH) using a Snow Water Equivalent Index (SWEI) derived from the High Mountain Asia Snow Reanalysis (HMASR) dataset. The analysis is limited to the 1999–2016 water years due to the unavailability of HMASR data for more recent periods. It is also noted that coarser-resolution datasets may be inadequate for capturing FsD events because of spatial heterogeneity in snow cover dynamics. Our results indicate the recurrence of flash snow droughts (FsDs) with varying durations, notably during February-March 2001, November-December 2010, and January 2011 and 2014. These FsDs fall within the moderate to severe drought categories, based on a threshold of −1. This study highlights the importance of FsD at the local scale for policymaking, mitigation planning, and integrated monitoring frameworks, and it identifies key research gaps to support resilient FsD management.