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

Abstract

At first, in this paper a general definition of the event rainfall-runoff erosivity factor for the USLE-based models, REF_e = (Q_R)^b1(EI₃₀)^b2, in which Q_R 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 REF_e. Then, the different expressions of REF_e were simultaneously tested against a dataset of normalized bare plot soil losses, A_eN, collected at the Sparacia (south Italy) site. As expected, the poorest A_eN 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 Q_R, 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.