Widespread declining trends of snow water resources and their driving factors in water towers of Indus River

Abstract The importance of seasonal snowpack in sustaining water resources for both ecological systems and anthropogenic activities is undeniable. Yet these vital systems are highly fragile and particularly susceptible to the impacts of human activities and climate change. The present study assesses the space–time variation in maximum snow water equivalent (SWEmax) and maximum daily snowmelt (SMmax) in terms of magnitude and timing and their response to variations in elevation, seasonal precipitation, and temperature which serve as an insightful indicator of hydrological change in snow water resources. The proposed framework combines long term daily snow water equivalent (SWE) and snowmelt data with multiple snow metrics, trend analysis, and attribution to seasonal temperature and precipitation, and is applied across the headwaters of the Indus River (Upper Indus Basin) for the period 1979–2019. Results show that the widespread loss in snow water resources has occurred across most parts of the UIB in recent decades especially at mid elevation and their trends are not linearly related to elevation and are highly heterogeneous between sub-basins. However, contrasting results are observed for cold dessert areas of UIB. Snow dominated basins, e.g., Jhelum, Chenab, and Swat, are the hotspots for the change in snow water resources, with significantly reduced and earlier snowpack and snowmelt peaks. These changes are primarily driven by temperature and precipitation, with their relative importance varying based on elevation and sub-basin characteristics. Specifically, the influence of precipitation and temperature on SWEmax is more strongly dependent on elevation, while winter melt (FMmax) is more influenced by sub-basin location. In contrast, SMmax exhibits variations in relative importance across both elevation and sub-basin scales. Negative changes in snow water resources in these mid-elevation zones have strong implications for downstream water availability.