Snow cover and snow water equivalent dynamics in the Upper Indus Basin (UIB) under current and CMIP6 climatic projections

Snow is an integral part of the climatic system, hydrological cycle and a significant moisture source. Among the basins in the high mountains of Asia, the Upper Indus Basin (UIB) generates snow and glacier melt contribution (70 % of the total river flow), the second highest after the Brahmaputra and Ganges. The climate is changing and its adverse impacts may have severe implications for melt-dependent river basins like the Indus. Therefore, simulating realistic snow cover and snow water equivalent dynamics is essential for understanding the hydrological processes and water resource management under current and future scenarios. This research aimed to analyse snow cover area (SCA) and snow water equivalent (SWE) dynamics for the Hunza basin (subbasin of the Indus) under current and future climatic conditions. A data-parsimonious precipitation-runoff model, Distance Distribution Dynamics (DDD), with its energy balance sub-routines for melt simulations, was forced with newly developed ERA5-Land (0.1°x0.1°) gridded datasets. The climatic projections derived from the Coupled Model Intercomparison Project Phase 6 (CMIP6) based general circulation models (GCMs) were used for future scenarios until the end of the 21st century. The model simulates SCA between 99 % of the study area (in January) and 10 % (in August) and SWE between 270–320 mm (in February) and 10–15 mm (also in August). The simulated SCA was validated using MODIS-driven SCA, and the results are promising. The Hunza River’s flow gets its maximum contribution from glacier melt (45–48 %), followed by snowmelt (30–34 %) and rainfall (21–23 %). Results also reveal that future SCA decreases significantly in all warming scenarios relative to the baseline scenario. Moreover, significant changes are expected in precipitation cycles and their timings, with increased liquid precipitation (rainfall) for the 21st century. These changes can significantly alter the downstream water availability, agricultural cropping patterns, and extreme flow conditions for snow melt-dependent regions like the Indus. The findings from the current study may provide helpful information about the snow and glacier melt contributions to future hydrological regimes.   Key Words: CMIP6, Energy Balance (EB), ERA5-Land, Hunza River basin, SCA, SWE, Upper Indus Basin (UIB)