Analysis of the Hydro-Climatic Regime of the Snow Covered and Glacierised Upper Indus Basin Under Current and Future Climates

In the high elevation Hindukush Karakoram Himalaya (HKH) mountain region, the complex weather system and sparse measurements make the elevation-distributed precipitation among the most significant unknowns and limit the realistic and comprehensive assessment of precipitation. In addition, due to local orographic effects, precipitation can vary highly over short horizontal distances. Accurate quantification of precipitation, however, is critical for understanding hydro-climatic dynamics. Moreover, snow and glacier dynamics, and their contribution to river flow in the HKH region, are also mostly unknown, leading to serious concerns about current and future water availability. The recent acceleration in climate change (CC) heightens concerns about future water availability from high elevation mountain regions. The HKH region heavily depends on its upstream frozen water resources, and an accelerated melt may severely affect future water availability. In line with rapid population growth in the Indo-Gangetic plain, there will be increased water, food and energy demands in the future. Therefore, increasing knowledge of the hydro-climatic regime and glacier and snowmelt contributions to the river flow under current and future climate change scenarios is essential. The Indus basin, with a downstream population of around 250 million, is among three highly populated river basins originating from the HKH mountains, followed by Ganges and Brahmaputra. This PhD research was designed to quantitatively and comprehensively assess precipitation and its distribution for the Gilgit and Hunza sub-basins of the Upper Indus Basin (UIB). In addition, the hydrological regime and snow and glacier dynamics were investigated, and the future hydro-climatic regime and water availability from the highly glaciated Hunza basin were analysed. For the present-day investigations, the elevation-distributed precipitation was derived from better performing global precipitation datasets which include the high resolution (0.1°x0.1°) and newly developed ERA5-Land, and a coarser resolution (0.55°x0.55°) JRA-55. These estimates were forced to a data parsimonious precipitation-runoff model, Distance Distribution Dynamics (DDD), with its energy balance and temperature index approaches for snow/glacier melt simulation. The model was calibrated from 1997–2005 and validated from 2006–2010. For future scenarios, the ERA5-Land corrected precipitation against the observed flow was employed to bias correct the precipitation from two global circulation models (GCM) using the newly released Coupled Model Intercomparison Project Phase 6 (CMIP6) climate projections. The DDD model was set up again using these bias corrected GCM projections for baseline (1991–2010), mid-century (2041–2060) and end-century (2081–2100) projections under Shared Socioeconomics Pathways (SSP) SSP1, SSP2 and SSP5 emission scenarios.