A Comprehensive Check of Usle-Based Soil Loss Prediction Models at the Sparacia (South Italy) Site

At first, in this paper a general definition of the event rainfall-runoff erosivity factor for the USLE-based models, REFe = (QR)b1(EI30)b2, in which QR is the event runoff coefficient, EI30 is the single-storm erosion index and b1 and b2 are coefficients, was introduced. The rainfall-runoff erosivity factors of the USLE (b1 = 0, b2 = 1), USLE-M (b1 = b2 = 1), USLE-MB (b1 ≠ 1, b2 = 1), USLE-MR (b1 = 1, b2 ≠ 1), USLE-MM (b1 = b2 ≠ 1) and USLE-M2 (b1 ≠ b2 ≠ 1) can be defined using REFe. Then, the different expressions of REFe were simultaneously tested against a dataset of normalized bare plot soil losses, AeN, collected at the Sparacia (south Italy) site. As expected, the poorest AeN predictions were obtained with the USLE. A distinction was made among the four power-type models since the fitting to the data was poor with the USLE-MR as compared with the other three models. Estimating two distinct exponents (one for EI30 and another for QR, USLE-M2) instead of a single exponent (USLE-MB, USLE-MR, USLE-MM) did not appreciably improve soil loss prediction. The USLE-MB and the USLE-MM were the best performing models.