Streamflow Simulation and Assessing the Land Use Changes impacts on it (Case Study: Gol Gol Catchment in The Province of Ilam, Iran)

The main purpose of this study was to simulate rainfall - runoff processes to assess the effects of land use changes on the runoff generation using the hydrological WetSpa model, and also to evaluate the accuracy of predicted daily discharge at the Gol Gol Catchment outlet, in Iran. The Nash Sutcliffe efficiency criterion was 0.603 for the daily discharge during the 2003 to 2009 period and the land use map of 2007. The results Further indicated that the land use have changed from 1988 to 2013, as forests and irrigated – gardens have decreased by 3322.502 and 3934.386 hectares (ha), respectively, while rangeland and rain-fed areas have increased by 3942.99 and 3313.9 ha, respectively. For assessing the effects of land use changes on the discharge, the simulated daily discharges generated by the model for the following years;1988, 2003, 2007 and 2013 were compared using the paired t-test. Results showed that there were significant differences at the 99% confidence level between the simulated discharges of 2003 and 2013 land use maps. The average annual discharge has increased from 1.118 m3/s in 2003 to 1.134 m3/s in 2013 due to this land use changes. Moreover, the mean daily discharge was increased by 15 l/s from the beginning to the end of the study period. In addition, there was a general increasing trend in the runoff volume