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This study deals with the simulation of snowmelt in a glacierized basin with higher temporal and spatial resolution. The study is based on extensive field work conducted on the East Rathong chu watershed in the Teesta River basin across its altitudinal range, glacier and snow cover areas. Degree day factor was determined at various altitudes and seasons in the glaciated catchment for 2017- 19. The field work included the operation of more than 10 micrometeorological stations across the transect of the Basin. Martinec developed SRM, which is a semi-distributed glacier melt model has been used to simulate the snowmelt runoff. SRM, uses a degree day method to envisage every day meltrunoff generation, using a melt coefficient to convert unit °C temperature above a threshold to mm of melt. The most sensitive parameters, Degree Day Factor (DDF) and Temperature Lapse Rate (TLR) were calculated by in-situ experiments and meteorological station data. DDF for snow and Ice have been estimated using glaciological and meteorological observation at the various altitudes in different seasons, which ranged from 6-13 mm day-1 °C-1. The magnitude of change of DDF of ice is almost twice of DDF of snow at the same altitude. The calculated TLR in Rathong Chu valley was −0.47 °C/100 m above the treeline and −0.52 °C/100 m below the Alpine Tree Line. The mean yearly TLR for Sikkim Himalayas for below and above the tree line was found to be less sheer than the Normal Temperature Lapse Rate. The computed annual average discharge was found to be 2.76 m3 s-1 in correspondence to the observed (2.76 m3 s-1) for the year 2018-19 and the resulting R2 was 0.94 proving the goodness of results. Further, to assess the impact of temperature variability on snow melt runoff various hypothetical scenarios were developed and snowmelt runoff was estimated for each scenario. The analysis showed that runoff in the summer season is likely to decrease more with the decreased temperature and precipitation. Whereas the stream flow is likely to increase more with the increased temperature and precipitation in the winter season.
