Glacio-hydrological variations in Shaune Garang Catchment, Western Himalaya

The rate of increase of temperature in Indian Himalayan Region is several folds higher than the global average and this trend is predicted to continue. The consequence of rising temperature is apparent on snow and glacier melt and form of precipitation. Present study aims at analyzing impacts of these changes on different glacio-hydrological processes in Shaune Garang, a small glacierized catchment in Western Himalaya. The comparison of area using satellite images from 1980 (Landsat 3) and 2014 (Landsat 8) indicate a clear reduction of glacierized area from 33% to 24% of the total catchment area upstream of discharge gauge. Despite the significant decrease in glacierized area, the debris-covered fraction of the glacierized area in the catchment reduced by just around 1%. The Shaune Garang glacier was observed to lose mass (-0.62 m w.e in 2013-14, -0.58 m w.e. in 2014-15 and -0.74 in 2015-16). A degree-day based glacio-hydrological model was developed, validated and applied in Shaune Garang catchment for basin wide mass balance discharge reconstruction. The degree-day factor (DDF) was estimated separately for snow covered (5.1±0.3 mm °C^-1 day^-1) and debris free ice covered (8.1±0.2 mm °C^-1 day^-1) area. For debris covered ice, separate DDFs were estimated for four different altitudinal bands varying from 2.6±0.4 mm °C^-1 day^-1 (4370-4573 m) to 9.3±0.3 mm °C^-1 day^-1 (4981-5185 m). The reconstructed mass balance using the model showed an average loss of 0.89 m w.e. per year (2001-2008) with slight mass gain during 2001-02 and 2004-05. The long-term discharge showed slight decrease (1985-2008) primarily caused by decrease in the percentage cover of glacierized area in the catchment. The assessment of percentage contribution of different components in the reconstructed discharge suggests that, snow melt stands for 33% and ice melt stands for 30% while the rest is contributed by rain and base-flow. The sediment load in melt season discharge from the catchment was observed to increase from 30 t day^-1 (1981-1991) to around 43 t day^-1 (2014-15). In addition, the physical weathering rate was also observed to increase by around 84 t km^-2 year^-1 during this period. The analysis of the concentration of different ions in the melt water suggests dominance of Ca²⁺ and Mg²⁺ cations and HCO₃^- anion.