Runoff Simulation using WetSpa Distributed Hydrological Model in Ziarat Watershed of Golestan Province, Iran

Aims Modeling precipitation-runoff processes and forecasting river flow are an essential step in floods management and controlling, designing water structures in watersheds and droughts management. Materials & Methods In the present research, WetSpa distributed hydrological model was applied to simulate river flow in Ziarat watershed of Golestan Province. This basin has an area of 95 km2 and it has an average height of 1760 m above sea level. As a distributed, continuous, and physical model, WetSpa is characterized with daily or hourly time series which accounts for processes of precipitation, runoff, and evapotranspiration contexts. The model parameters include distributive and global parameters. To run model, daily data on flow, precipitation, temperature, and evaporation for years 2008–2016 were considered for calibration and validation. Findings The results of simulation showed a relatively good compatibility between calculated and measured hydrograph at the basin outlet. According to Nash-Sutcliffe model for calibration periodic model, efficiency coefficient estimated daily hydrographs and maximum flow rate by 57.32% and 84.11% accuracy, respectively. However, given Nash–Sutcliffe coefficient which was equaled to −385.39 and −209.06 for low and high flow, respectively, validation results are not acceptable which it can be attributed to water withdrawal and diversion dam for water harvesting before gauging stations in outle. Conclusion Given the calibration results, WetSpa model has great efficiency under high flow circumstances compared to low flow mainly due to model weakness in low flow estimation but as a whole model simulated total flow with acceptable accuracy.