Investigating the factors involved in the curve number rainfall-runoff model

Estimating the amount of surface runoff and studying the relationship between rainfall and runoff is the most important issue in surface water hydrology studies. Using simple methods to estimate runoff in hydrological applications, especially in ungauged watersheds, is of particular importance. Probably the simplest conceptual method for predicting runoff depth is the use of the curve number rainfall-runoff model, which was originally developed to model the depth of runoff caused by rainstorms in small agricultural and rangeland catchments, but so far it has been applied in applications other than those originally intended. Various studies show that this method is still growing and improving and it needs to improve. In the present study, firstly, a review of the studies that investigated the factors involved in the curve number method to estimate the runoff value was done, and one of the main results of these studies is to suggest changing the value of the standard initial loss ratio (that is, changing the value of λ from 0.2 to 0.05) based on extensive field measurements and also considering rainfall-runoff response classes when using the curve number method. Secondly, some remaining challenges and future perspectives regarding this method are mentioned.