Determining the Snow Coefficient in Order to Simulate the Snow Melting in the Shemshak Watershed Using the WetSpa Model

In mountainous regions, snow forms a part of the precipitation. Therefore, snow melting is an important process in hydrology and hydraulic in these areas that its role should be considered independently in runoff generation. The Shemshak watershed basin located in Tehran province was selected as the study area of this research to examine the efficiency of the WetSpa hydrologic model to simulate the runoff generated from snow melting in a 12-year period (2002-2014). Spatially distributed model of WetSpa simulates various hydrological processes such as snow melting using degree-day method in a cell and on hourly and daily time scales. Different hydrologic processes in this research are simulated by the WetSpa model using climatic data (rainfall, temperature, evaporation, and discharge) and spatial maps (land use, soil texture, and Digital Elevation Model). Evaluation of the model performance to simulate the daily hydrograph based on the Nash-Sutcliffe and Kling-Gupta showed that the values of these criteria are 71.3% and 83%, respectively. based on the results, the WetSpa model has a good capability to simulate the runoff generated from snow melting in the daily time scale. Also, the snow coefficient for the study region was 0.28.