Integrated simulation of snow and glacier-melt runoff in a distributed biosphere hydrological framework; case studies at Nepal Himalaya and Pakistan Karakoram meso-scale basins

An advanced multilayer energy budget based glacier melt scheme and snow melt scheme have been integrated to the distributed biosphere hydrological model for accounting the complete water and energy cyclic components for the improvement of land surface-atmosphere interactions. The integrated model, named WEB-DHM-S, can be applied to the river basins with various surface characteristics (different vegetation,, snow, bare land, debris covered and debris free glaciated regions) for water resources assessment. In this study, the model capability was shown at two meso-scale river basins; Narayani basin in Nepal Himalaya (32000 km²) and Hunza basin (13000 km²) in Pakistan Karakoram, with different climatic characteristics. Winter accumulation is dominant in Hunza basin whereas summer accumulation is dominant in Narayani basin. The simulations were carried out at hourly time scale at 1km spatial resolution for the years 2002 and 2003 by using Global Land Data Assimilation System (GLDAS) atmospheric forcing (except observed temperature and precipitation). The snow and glacier melt runoff along with rainfed runoff, spatial distribution of seasonal snow and glacier cover, and glacier mass balances were simulated. The results for discharge simulation showed that the simulated and observed discharge were in good agreement at both basins (Nash efficiency above 0.90). The grid-to-grid analysis of the simulated snow cover area and the Moderate Resolution Imaging Spectroradiometer (MODIS) derived eight-day maximum snow-cover extent data (MOD10A2) demonstrated that the model accuracy was about 85%. The contribution of snow and glaciermelt was about 85% in Hunza basin and about 4% in Narayani basin. This study provides a benchmark for potential application of such integrated model (WEB-DHM-S) to entire Hindukush Himalaya and Karakoram region in simulating the snow and glacier hydrological processes.