Incorporating snow model and snowmelt runoff model for streamflow simulation in a snow-dominated mountainous basin in the western Hindukush-Himalaya region

A Snow Model (SM) using a temperature-index method was used to optimize the degree-day factor (DDF) and precipitation gradient (PG) for the different elevation zones of the Panjshir sub-basin for snowmelt runoff modelling. The values derived for DDF and PG were calibrated and validated by comparing observed snow cover area and snow cover area simulated by SM. The Snowmelt Runoff Model (SRM) was used to simulate daily runoff over the hydrological years 2009-2014 using the optimized values for SRM accuracy. The optimized DDF values were 0.3 to 0.9 (cm degrees C-1 d(-1)) for elevations from 1593 m to 5694 m. Meanwhile the PG was +0.002 m(-1) for elevations 1593-4000 m and 0 m(-1) above 4000 m. The simulated runoff by SRM during the entire data period correlated very well with a Nash-Sutcliffe coefficient NS = 0.93 utilizing both observed and simulated snow cover area. This method not only evaluates the characteristics of snowfall and snowmelt in different elevation zones to obtain the DDF and PG, but can also estimate the snowmelt runoff.