Estimating the R factor from daily rainfall data in the sub-Mediterranean climate of southwest Slovenia

Rainfall and runoff play an important role in the process of soil erosion, which is usually expressed with the R factor. To calculate the R factor, long-term precipitation data are needed with high temporal resolution, typically available for only few locations. The aim of this study was to obtain an approximate relationship between the more commonly available daily precipitation data and the R factor. A set of equations is presented for calculating monthly and annual R factor values based on daily precipitation data for a sub-Mediterranean region in southwest Slovenia, and their applicability is discussed. The sum of squares of daily precipitation was found to be the best descriptor of the monthly R factor. The ratio between the R factor and the sum of squares of daily precipitation varies throughout the year and generally follows the mean monthly temperature, with the efficiency coefficient, e, of 0.869 between predicted and observed data on the annual basis.