The concept of Variable Source Areas (VSAs) depicts that runoff is generated by the mechanism of saturation-excess in different times and spaces within watersheds. Identification of VSAs allows exploring the hydrologically sensitive areas of a watershed which generate more runoff and have higher potential of delivering contaminants to streams. A hydrological model was developed to simulate variable source areas of a small agricultural watershed in southern Ontario. Two summer storms of August 9, 2008 and August 10, 2008 were selected to evaluate the capability of the model for VSA simulation. Calibration of model resulted in the Nash-Sutcliffe model efficiency coefficient of 63% with relative errors of 12%, 23%, and 0% for peak flow, total flow, and time to peak. Application of model for the second storm was tested with Nash-Sutcliffe coefficient of 28%. Simulation of VSA showed a high efficiency of the model to identify the locations of source areas in the watershed which generate more runoff and have higher potential of delivering contaminants to streams.
