Changes in Snow-glacier and their Impacts on Melt Runoff in the Himalayan River Basin

This study has been performed over the Upper Bhagirathi River basin (up to Maneri), Himalayan region, India to analyze the impact of snow-glacier changes on the melt runoff (1986-2020). In this study, a fully distributed snow and glacier melt runoff model viz. Spatial Process in Hydrology (SPHY) has been used, which incorporates the variable degree-day factors-based temperature index model to compute the snow and glacier melt runoff, separately. For the assessment of glacier changes and corresponding melt runoff, different glacier maps (i.e. for years 2000 & 2020) have been prepared using LANDSAT imageries. The SPHY modeled runoff (Q) and observed Q induced by snow and glacier melt have shown a good agreement at Maneri (~84%). A noticeable reduction in the glacier areas has been observed (~5.6% mass reduction in 30 years) and therefore, an increase in glacier melts at outlets. Similarly, a noticeable decrease in snow melt runoff has been computed (~3%-4%). The contribution from rainfall runoff has been enhanced (~3%). The 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). These observations have immediate consequences for policy making for the management of water resources in the glaciated catchments of the Himalayan regions.