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The hydrological cycle in a catchment is sensitive to climate and land-use changes. The authors conducted a case study to validate the performance of the soil and water assessment tool (SWAT) and its applicability as a simulator of runoff and sediment transport processes at the mesoscale scale in arid and semiarid areas. SWAT is used to simulate runoff and sediment changes caused by human activities in a typical watershed, the Jihe Watershed (1,019 km(2)), in the Loess Plateau of northwestern China. A marked increase in temperature was observed over the analysis period. The investigation was conducted using 47 years of historical rainfall/runoff data and sedimentary records from 1962-2008. The data from 1962-1981 was used for calibration and that from 1982-2008 for validation. The results showed that the Nash-Sutcliffe model efficiency coefficient was approximately 0.7, the relative error was less than 15%, and the coefficient of determination was greater than 0.7, both for annual flow and sediment yield in the calibration period. These findings indicate that the SWAT model was able to simulate runoff and sediment yield satisfactorily; however, it exhibited better performance for the calibration period than for the validation period. Similarly, simulations of monthly flow and sediment were better for the calibration period. The simulated and observed values agree well with trend changes. Uncertainty analysis indicates that digital elevation model resolutions and watershed subdivisions imposed little influence on annual flow, but notable effects were observed with respect to annual sediment yield. DOI:10.1061/(ASCE)HE.1943-5584.0000629. (C) 2013 American Society of Civil Engineers.