Impact of climate change on the hydrological projections over a western Himalayan river basin and the associated uncertainties

Melt water from snow and glaciers is a major contributor to the streamflow over the Himalayan mountainous region. However, rising temperatures and uncertain precipitation trends may change the timing of snow melt and snow accumulation, altering the hydrological cycle. This study investigated future hydrological changes and the associated uncertainties over a snow-fed catchment of the western Himalayan River, Astore. A process-based hydrological model (WRF-Hydro/Glacier) was used with meteorological forcing from global climate models (GCMs), bias correction methods (BCMs), and multiple optimized hydrological parameters (MPs). The simulated results of streamflow, the snow-covered area (SCA), and evapotranspiration (ET) were examined over three periods: baseline (BL; 2000–2019), mid-future (MF; 2040–2059), and far-future (FF; 2080–2099). With early snow melt and late accumulation of snow, the peak streamflow is projected to shift from July during the BL, to mid-June during MF, and to mid-May during FF. Moreover, a decrease in the SCA and an increase in ET was projected during both MF and FF periods, leading to reduced solid water reserves in snow and glaciers. Furthermore, by quantifying the uncertainty contribution of GCMs, BCMs, and MPs in projecting future hydrological components, it was determined that more emphasis should be placed on the selection of an appropriate GCM and MP than that of a BCM in projecting streamflow and SCA. When projecting SCA, the GCM and MP are major contributors to uncertainty in fall–winter and spring–summer, respectively. Conversely, when projecting ET, GCM and BCM have more influence than MP. Overall, this study highlights the importance of uncertainty assessments to develop robust adaptation plans in ensemble-based climate change projections over the western Himalayan region.