Author(s): Muhammad Usman Liaqat; Roberto Ranzi
Keywords: Snow and Glaciers fed areas; Climate change; Energy balance modelling
Abstract: Energy budget-based distributed modelling in High Mountain Asia (HMA) is important to examine glaciological-hydrological regimes and compute flow rates in current and projected scenarios. Trends in ablation of snow and glaciers retreat depend upon snow and ice reserves, meteorological parameters and geographical features which vary across sub-basin in HMA. In this study, the Physical Based Distributed Snow Land and Ice Model (PDSLIM, Ranzi et al., 1991; Grossi et al., 2013) is employed in the HMA for the Naltar catchment (area of 261.70 km2, with 45 km2 glacierized) located in the Hunza river basin (Karakorum, Pakistan) to simulate snow and glacier melt progression as well as daily runoff. The overall objective is to verify the feasibility of this modelling system to assess the impact of climate and land use change scenarios. Another objective is also to address the so called “Karakorum anomaly” in glaciers’ dynamics, as some glaciers exhibited advances in the last period. The accuracy of the model in simulating distributed snow cover is crosschecked using MODIS and LANDSAT based snow cover areas both at temporal and spatial scale. The results exhibited overall satisfactory performance of coefficient of determination (R2) = 0.97 and Nash-Sutcliffe Efficiency (NSE) = 0.96 of model against satellite-based snow cover area for all simulated melting periods. Downstream daily runoff measurement at the outlet of Naltar catchment at Naltar Bala station was used as a reference of comparison for simulated summer streamflow. Runoff simulations revealed good agreement with observed discharge NSE of 0.88 and 0.90 for calibration and validation period respectively. The increasing runoff volume in late spring and early summer is associated with rising rate of temperature, as no significant precipitation changes have been recorded. However, net simulated runoff volume computed by PDSLIM was in reasonable agreement and only 1.04 times higher than mean observed runoff volume with mean absolute percentage error of 8%. Flow composition analysis revealed snow-glacier melt runoff provides the largest contribution to river discharge. Overall, PDSLIM, so far tested in the Alps, showed to perform well also for snow- and glacier-dynamics in the glacierized catchments of HMA. The hydrological response to projected climate scenarios is currently being investigated.