Comparative impact assessment and modelling analysis of river basins in the data-scarce upper Indus Basin

The meltwater from snow and glaciers in the data-scarce mountainous regions of the upper Indus Basin (UIB) confronts significant concerns due to climate change, the consequential cryospheric changes in snow cover dynamics and glacier mass balance are altering hydrological regimes through seasonal streamflow shifts. Taking the UIB as a study area, season dynamics and long-term trends in hydro-meteorological time series was analyzed, and a high-quality meteorological forcing dataset was developed for driving a distributed hydrological model (J2000). The Hydrograph Partitioning Curves (HPC) method was used to assist in model calibration and mitigated uncertainty. Water balance and the distributions of different runoff components in the UIB were further quantified. Our analysis indicates that winter and spring runoff in several sub-basins of the UIB exhibits an increasing trend, characterized by earlier snowmelt runoff timing and considerable regional variability. The timing of runoff center advancement is significantly influenced by the snow fraction (SF). When SF is less than 0.8, alterations in the timing of runoff centers are predominantly influenced by precipitation; when SF exceeds 0.8, these changes are principally dictated by the timing of snowmelt. We included environmental factors, including elevation and NDVI, to facilitate regional downscaling of the TRMM grid-based precipitation product, which was subsequently employed to drive a hydrological model for analyzing runoff processes in the typical Gilgit, Shyok, and Kharmong basins of the UIB. Among these three basins, the Gilgit Basin experiences a precipitation of 793 mm and an evapotranspiration of 334 mm, with snowmelt and glacial melt runoff constituting 34% and 28% of the total runoff, respectively. In the Shyok Basin, precipitation measures 539 mm, evapotranspiration is 289 mm, and snowmelt and glacier melt runoff account for 26% and 41% of the total runoff, respectively. The Kharmong Basin experiences the lowest precipitation at 392 mm, with an evapotranspiration rate of 243 mm, while snowmelt and glacier melt runoff contribute 36% and 25%, respectively. This study provides valuable insights into hydrological changes in the UIB, and underlying methodology can be important for other modelling studies in data-scarce basins and in the context of climate change.