Effects of Climate Change on the Hydrological Regime of a Mountainous Catchment: A Case Study from the Hindu Kush Himalayan Region

Mountainous basins account for approximately 22% of the global population and exhibit high sensitivity to climate change, underscoring the importance of assessing future water availability in these areas. This understanding is particularly crucial for Himalayan catchments like the Upper Indus Basin (UIB), where snow and glacier melt contribute substantially to streamflow. To understand the impacts of climate change on these critical water resources, employing multiple hydrological models offers a comprehensive framework for evaluating diverse hydrological responses, accommodating different scenarios and uncertainties for more reliable predictions. In this study, initially, we calibrated and validated four semidistributed conceptual hydrological models integrated with a degree-day snow module in the UIB. Future streamflow projections were generated using bias-corrected data from 17 Coupled Model Intercomparison Project 6 (CMIP6) models, representing shared socioeconomic pathway (SSP) scenarios, namely, SSP245 and SSP585 scenarios. The streamflow generated by each hydrological model for each scenario from the 17 global climate models (GCMs) was averaged using Bayesian model averaging to create a multimodel ensemble. The results indicated an anticipated decline in discharge by the end of 2100 across all four models, with the SSP585 scenario showing higher variability and magnitude than SSP245. Spatial analysis revealed that the percentage change in overall future discharge across UIB subbasins exceeded 50%, with notable declines in Gilgit, Hunza, Shigar, and Astore Basins, where changes fell below −30%. Further, the results also indicated a distinct shift in the hydrological patterns during the summer monsoon by the end of the century, driven primarily by anticipated changes in glacier cover. Overall, this study offers valuable insights into the shifting hydrological patterns in complex mountainous terrain due to changes in glacier cover, while presenting an approach that can be effectively applied to other data-scarce catchments.