Incorporating a Rainfall Intensity Modification Factor γ into the Ia-S Relationship in the NRCS-CN Method
Rainfall intensity is a key factor that influences the processes of infiltration and runoff generation on the surface soil. However, the Natural Resources Conservation Service runoff curve number (NRCS-CN) method, which is widely used to simulate direct runoff, does not consider the impact of rainfall intensity on the simulation results. Hence, this study incorporates a rainfall intensity modification factor (γ) into the Ia-S relationship in the NRCS-CN method. The results show that the modified method, the NRCS-CN-γ method, improves the efficiency, reduces the impact of variable rainfall intensity on the simulation results and reduces the relative errors caused by the changes in CN to approximately one-third of the original errors in the NRCS-CN method. Consequently, the NRCS-CN-γ method contributes to a more accurate simulation and prediction of direct runoff in monsoon regions where rainfall intensity greatly varies, especially under climate change.