Components of Himalayan River Flows in a Changing Climate

Assessment of the response of the Himalayan river flows to climate change is complex due to multiple contributors: rainfall, snowmelt, and glacier-melt. The number of studies is limited in this direction due to lack of data availability as well as non-availability of models considering all the above-mentioned components. As for example, the state-of-the-art variable infiltration capacity (VIC) model does not account for the glacier melt. Here we integrate a glacier-melt model with VIC and validate the model output with observed streamflow in five river basins in the Himalayas, at daily scale. Our model simulates the streamflow with Nash-Sutcliffe estimates greater than 0.65 in all basins. The sensitivity analysis shows that the contribution from snowmelt decreases substantially in all the five basins with 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%. Climate model simulations show a decrease in the spring onset times for Sutlej basin while increase for DK basin for both RCP4.5 and RCP8.5 scenarios. Sutlej and Arun basins show decreases of more than 6 days in the center of volume of streamflow, which suggests that there will be increased flows in the early part of year and reduced flows later in the year.

Automated summary

This study integrated a glacier-melt model with the VIC model to simulate and validate river flows in five basins in the Himalayas, revealing the complex impact of climate change on river flows. The research found that the contribution of snowmelt decreases while glacier-melt increases in a warmer environment, but decreases significantly when glacier volumes are reduced. However, this decrease can be compensated by increased precipitation in a wetter scenario.