Bivariate analysis of rainfall characteristics for identifying soil loss return periods at the event scale

• Joint return period for rainfall depth H and 30-minute max intensity I30 in each season. • Relationships between the joint return period of H and I30 and event-scale soil loss. • Soil conservation strategies based on the return period of event soil loss. In this work, a method was developed to associate a return period with event soil loss at the plot scale ( SL e ) based on the joint return period RP of event rainfall height H and maximum 30-minute intensity I30 . The analysis used rainfall and SL e data from bare-soil plots of varying lengths with a 16% slope at the SERLAB site (central Italy). H and I30 were well described by the Generalized Pareto Distribution, and their dependency structure was modeled with a non-parametric copula. Marked seasonal differences emerged in the joint probabilistic behavior of H and I30 . A regression analysis between the normalized soil loss SL N , (relative to the mean value μ SL e for each plot length) and RP identified linear, season-specific relationships. The slope coefficients (1.16·10 −4 , 2.05·10 −3 , 8.33·10 −3 , and 8.73·10 −4 for winter, spring, summer, and autumn, respectively) clearly indicate that a given SL N , corresponds to different RPs depending on the season. The confidence intervals of the coefficients, besides reflecting experimental uncertainty, indicate system vulnerability (e.g., due to the temporal variability of soil erodibility). Finally, the study outlines a practical procedure for applying these relationships in soil conservation planning.