In hydrological models, soil conservation services (SCS) are one of the most widely used procedures to\r\ncalculate the curve number (CN) in rainfall run-off simulation. Recently, another new CN accounting\r\nprocedure has been mentioned, namely the plant evapotranspiration (ET) method or simply known as\r\nthe plant ET method. This method is embedded in the Soil and Water Assessment Tool (SWAT) model\r\nwhich has been developed for watersheds covered by shallow soils or soils with low storage\r\ncharacteristics. It uses antecedent climate and plant evapotranspiration for calculation of daily curve\r\nnumber. In this study, the same method had been used to simulate the daily stream flow for Roodan\r\nwatershed located in the southern part of Iran. The watershed covers 10570 km2 and its climate is arid\r\nto semi-arid. The modeling process required data from digital elevation model (DEM), land use map, and\r\nsoil map. It also required daily meteorological data which were collected from weather stations from\r\n1988 to 2008. Other than that, the Sequential Uncertainty Fitting-2 (SUFI-2) algorithm was utilized for\r\ncalibration and uncertainty analysis of daily stream flow. Criteria of modeling performance were\r\ndetermined through the Nash-Sutcliffe and coefficient of determination for calibration and validation.\r\nFor calibration, the values were reported at 0.66 and 0.68 respectively and for validation; the values\r\nwere 0.51 and 0.55. Moreover, percentiles of absolute error between observed and simulated data in\r\ncalibration and validation period were calculated to be less than 21.78 and 6.37 (m3/s) for 95% of the\r\ndata. The results were found to be satisfactory under the climatic conditions of the study area.
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