An assessment of snow-glacier melt runoff under climate change scenarios in the Himalayan basin

In this study, a coupled and improved snow-glacier runoff modeling framework has been presented, which aims to separate the snowmelt runoff from glaciated and non-glaciated areas. To fulfil the above objective, the two hydrological models such as the conceptual Glacier-hydrological Model (GSM-SOCONT) and Soil & Water Assessment Tool (SWAT) have been used over the Teesta river Himalayan catchments. The temperature index model (TIM) based degree-day approach (DDA) in GSM-SOCONT model has been modified and radiation components were added. The R2 values computed between observed and modeled discharge (1991–2005) was improved from 0.55 to 0.63 after adding the radiation components. Initially, SWAT model has been used for the simulation, calibration, and optimization of the various snowmelt hydrology parameters. Then, SWAT model based optimized parameters and outcomes were used as inputs to set up the GSM-SOCONT model. After simulating/separating snow melts from glaciated and non-glaciated areas, the optimized snow-glacier parameters from the improved GSM-SOCONT (1991–2005) were re-input to the SWAT for the projection of snowmelt scenarios (2008–2100) utilizing the downscaled Coupled Model Intercomparison Project Phase 5 (CMIP5) Global Circulation Models (GCMs) datasets. The snow water equivalent (SWE) reconstructed for the year 2005 from the MODIS satellite snow covers (i.e. ranges from 80 to 138 mm) found comparable to the SWAT generated SWE (i.e. ranges from 86 to 115 mm). Based on the future projections of snowmelt, the earlier snow-melting or shifts have been observed in extreme high and low elevation areas of the Sikkim Himalaya.