Glacier changes and their impacts on the melt runoff in high and moderate elevation ranges of Himalayan Upper Ganges Basin

Abstract The rise in temperatures over the Himalayan regions due to climate change have shown profound effects on the seasonality and long‐term availability of snow melt runoff and glacier melt runoff. As per the sixth assessment report by the Intergovernmental Panel on Climate Change, the Himalayan glaciers are retreating and the fraction of precipitation falling as snow is altering. This study analyses the effect of snow‐glacier changes on the melt runoff (1986–2020) over the Upper Ganga river basin (up to Rishikesh) using a fully distributed model namely, Spatial Process in Hydrology (SPHY), which governs by Temperature Index Model approach with varying degree‐day factors. This study performs the two‐step calibration approach for model parameterization and to evaluate the snow and glacier melt runoff utilizing the observed discharge and real time satellite datasets. The SPHY derived snow cover was compared with the Moderate Resolution Imaging Spectroradiometer (MODIS) derived snow covers. Results show that the SPHY modelled fractional snow covers found comparable to MODIS derived snow covers (~70%–90% correlation). The R 2 based comparison of SPHY modelled runoff ( Q ) and observed Q at two gauges namely, Maneri (~0.85) and Rishikesh (~0.80) found reasonable. For the assessment of glacier changes and corresponding melt runoff, temporal glacier maps (i.e., for years 1990, 2000, 2010, 2020) were prepared utilizing the Landsat imageries. Results showed a noticeable reduction in the glacier areas (~5% mass reduction in 30 years) and an increase in glacier melt runoff at different stations (e.g., at Bhojwasa ~3%–4% and at Rishikesh ~1%–2%). Similarly, a decrease in snow melt runoff (~3%–4%) and an increase in rainfall runoff (~3%) were computed. A month wise percent of change analysis has shown significant fluctuations in the magnitude and seasonality of all runoff components (i.e., snow Q , glacier Q , base Q and rainfall induced Q ) in the Himalayan Upper Ganga basin.