Runoff simulation considering time-varying partial contributing area based on current precipitation index

Partial contributing area (PCA) denotes the region of a watershed near saturation and contributing surface flow to streams. The objective of this study was to incorporate the time-varying PCA concept into hydrological modeling for runoff simulation. In order to provide an accurate estimation of the temporal PCA ratio, a current precipitation index (CPI) was adopted to simulate the continuous change of water content in soil and to estimate the antecedent soil moisture at the beginning of a rainstorm. Information on the time-varying PCA ratio was then combined with a geomorphology-based runoff model for hydrograph simulation. The proposed model was applied to two watersheds, one in the United States of America and the other in Taiwan, to demonstrate its capability for runoff simulation. The results showed that the CPI can provide adequate estimations on time-varying PCA ratio. The simulated hydrographs of the test storms for the two study watersheds were found consistent with records. A set of representative parameters obtained from model calibration in the study watersheds can be a reference for practical uses in the watersheds with similar geomorphologic and hydrological conditions.