Runoff curve number, and it's variability in the estimation of storm runoff

The runoff curve number (CN) method, is a simple empirical technique developed by the US. The Soil Conservation Service (SCS), is used for estimating the depth of surface runoff from rainfall events. This technique was originally devised for application in agriculture, and forest watersheds, but later was extended by the SCS to include urban watersheds, and presently is used around the world. However, after four decades of application, it is necessary to review and re-examine it to determine further development. The purpose of this paper is to review the original intent, development, application, limitations, and present day interpretations of this method, and assess some remarks in this procedure. This approach has been applied to the Iranian representative basins, and the curve number of the observed values show that observed CN values deviate from the extracted values from the SCS handbook, for the same catchment characteristics.