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Abstract:
Climate change response assessment of the Himalayan river flows is a complex problem due to multiple contributors: rainfall, snowmelt, and glacier melt. Due to a lack of data availability and models that consider all of the factors mentioned above, the number of studies in this approach is constrained. For instance, the variable infiltration capacity (VIC) model does not consider glacier melt. In our work, we combine a glacier-melt model with VIC and validate the model's results using daily streamflow observations from five river basins in the Himalayas. In all basins, our model replicates streamflow with Nash-Sutcliffe estimates over 0.65. The sensitivity analysis shows that the contribution from snowmelt decreases substantially in all five basins, with the highest decrease of 36% in Dudh Kosi (DK) in a warm and dry scenario. The glacier-melt increases (15%–70%) in a warmer environment with its present volume but decreases (3%–38%) substantially when the volumes are reduced to half. However, such a decrease is found to be compensated by increased precipitation in a wetter scenario with a net increase of 3%–13%. For both the RCP4.5 and RCP8.5 scenarios, climate model simulations indicate that the Sutlej basin's spring start periods are decreasing while they are increasing for the DK basin. The centre of streamflow in the Sutlej and Arun basins shows declines of more than six days, indicating higher flows early in the year and lower flows later. Understanding different streamflow components is also important to understand how extreme precipitation events translate into hydrologic extremes.
