Determining and predicting single-storm erosion index in Sicily

The single-storm erosion index, Re, expressing the rainfall erosive power, can be either calculated or estimated and it can be used for a variety of analyses, including the probabilistic assessment of soil water erosion phenomena. Calculation of Re according to the original procedure requires rainfall depth, he, and intensity data at short time intervals but their temporal resolution can change with the considered recording rain-gauge station. Estimating Re is sometimes necessary since rainfall intensity data could be unavailable in certain circumstances. An appropriate probability distribution law of the annual maximum values of Re has to be chosen for predicting single-storm erosivity values with a given return period. With reference to 8464 erosive rainfall events collected at 26 Sicilian stations in the 2002-2024 years, this investigation showed that: i) Re calculated by rainfall data measured at Delta t = 30 min time intervals constituted the 88% of the corresponding calculations obtained by rainfall data collected at Delta t = 10 min and time effects were particularly appreciable for relatively small rainfall depths (he <= 40 mm); ii) the power law relationship between Re and he parameterized by minimizing the sum of the squared residuals between the actual and the estimated Re values (optimization approach, OPT) yielded less biased Re predictions than the relationship parameterized by a linear regression analysis of the natural logarithm (ln-) transformed data; iii) power law relationships obtained in two different historical periods (1951-1970 and 2002-2024) yielded different Re predictions, likely as a consequence of climate change; iv) an envelope line of the Re vs. he data was usable to simply distinguish, for a given rainfall depth, expected from unexpected, Re values; and v) the annual maximum values of Re were distributed according to the Extreme Value Type-1 (EV1) distribution. In conclusion, rainfall temporal resolution effects on Re calculation can be expected to decrease as he increases. The OPT approach should be applied for parameterizing the Re predicting relationship. Using Re vs. he relationships developed in the past for estimating current erosivity is not recommended. The highest expected Re value for a given rainfall depth and the quantile, ReT, corresponding to a given return period, T, can easily be estimated and they should be taken into account for planning appropriate soil conservation measures given that total soil erosion in a long period is mostly due to a few particularly high erosive events.