Preferential flow is significant for its contribution to rapid response to hydrologic inputs at the soil surface and unsaturated zone flow, which is critical for flow generation in rainfall–runoff (RR) models. In combination with the diffuse and source-responsive flow equations, a new model for water infiltration that incorporates preferential flow is proposed in this paper. Its performance in estimating soil moisture at the catchment scale was tested with observed water content data from the Elder sub-basin of the South Fork Eel River, located in northern California, USA. The case study shows that the new model can improve the accuracy of soil water content simulation even at the catchment scale. The impacts of preferential flow on RR simulation were tested by the Modello Idrologico Semi-Distributio in continuo lumped hydrological model for the Elder River basin. Eleven significant floods events, which were defined as having flood peak magnitudes greater than ten times average discharge during the study period, were employed to assess runoff simulation improvement. The accuracy of the runoff simulation incorporating the preferential flow at the catchment scale improved significantly according to the likelihood ratio test.

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