Comparison of direct outflow calculated by modified SCS-CN methods for mountainous and highland catchments in upper Vistula Basin, Poland and lowland catchment in South Carolina, U.S.A
The aim of the study is to compare direct outflow from storm events estimated using modifications of original SCS-CN procedure. The study was conducted in a mountainous catchment of Kamienica River and a highland catchment draining Stobnica River located in Upper Vistula water region, both in Poland, and a headwater lowland watershed WS80 located at the Santee Experimental Forest in South Carolina, USA. For estimating the event outflows for the Kamienica and Stobnica River basins, the initial data on observed rainfall-runoff events for years 1980-2012 were obtained from Institute of Meteorology and Water Management, National Research Institute in Warsaw, Poland. Similarly, data on rainfall-runoff events for watershed WS80 for a period of 2008 to 2011 were obtained from the United States Department of Agriculture (USDA) Forest Service, Santee Experimental Forest in South Carolina, U.S.A. Following methods were used for the evaluation of event outflows for the three study sites: SCS-CN, Ajmal method, MS method, and Sahu 1p and 3p methods. Results from the examined models revealed that the best results of estimated direct event outflow, based on model evaluation statistics (Nash-Sutcliff efficiency parameter), for analyzed catchments were obtained using the Sahu 3p model. However, direct outflow estimated using the original SCS-CN method was underestimated in comparison to the observed ones for most of the analyzed episodes.