Testing the USLE-M family of models at the Sparacia experimental site in south Italy

The modified Universal Soil Loss Equation (USLE-M) was empirically deduced by a statistical analysis of the original data set of soil loss measurements used to derive the Universal Soil Loss Equation (USLE). The USLE-M, including the effect of runoffin the event rainfall-runofferosivity factor, is characterized by a better capacity to predict event soil loss. At first, in this paper, using the soil erosion representative variables of USLE-M and the reference condition adopted in the USLE, the dimensional analysis and the self-similarity theory are applied to theoretically deduce a multiplicative equation similar to the USLE-M. Then using the database of the Sparacia experimental site, the ability to predict event soil loss by the USLE-M and modified USLE-M (USLE-MM) models are tested. The analysis demonstrates that the relationships used to predict the topographic factors of USLE-MM can be applied in areas different from the one of its original derivation. Finally, the analysis shows that, overall, USLE-MM [Nash-Sutcliffe index (NSEI) = 0.80; root mean square error (RMSE) = 10.3] performed slightly better than USLE-M (NSEI = 0.75; RMSE = 11.4) whereas the soil loss prediction accuracy especially improved for the relatively low and the highest values. In fact, for event soil loss per unit area (Ae) < 10 Mgha-1 the RMSE was equal to 7.1 for USLE-M and 4.4 for USLE-MM, and for Ae > 100 Mgha-1 the maximum factor of difference between predicted and measured soil losses was equal to 1.8 for USLE-M and 1.2 for USLE-MM.