Distributed Modelling of Snow and Ice Melt in the Naltar Catchment, Upper Indus Basin

Energy balance distributed modelling in High Mountain Asia (HMA) is important to examine glaciological and hydrological processes and assess changes in streamflow in the current and future climate. In this study, the Physically Based Distributed Snow Land and Ice Model (PDSLIM) using detailed observed data at hourly scale is employed for the hydrology of the Naltar catchment located in Hunza river basin (Karakoram, Pakistan) to simulate snow cover and glacier retreat as well as daily runoff. The results exhibited overall satisfactory performance in terms of coefficient of determination (R2 = 0.96) and Nash-Sutcliffe Efficiency (NSE = 0.95) modelled against satellite-based snow cover areas, for internal model verification, in eight years. The results of runoff simulations compared for external model verification, with observed daily discharge resulted in NSE 0.90 and 0.89 for calibration and validation period respectively. Flow composition analysis revealed that the streamflow regime of Naltar catchment is composed to 40% by glacier runoff, 42% by sub-surface runoff and 18% by surface runoff. The eight year mean value of net mass balance exhibited a slightly negative mass balance (-0.81 ± 0.31 m w.e. a-1) less pronounced than that observed globally in continental glaciers distinct from the
iceland and Antarctic ice sheets (Hugonnet et al.2021 and Zemp et al.2019). Overall, the distributed energy-balance model PDSLIM, so far tested in the Alps, results to be a suitable tool to estimate energy and mass balance in the glacierized catchments of Karakoram and Himalaya and to better understand snow and icemelt runoff dynamics and floods in highly complex and glacierized mountain basins.