Recent research has shown a lack of long-term monitoring for detailed analysis of gully erosion response to climate characteristics. Measures carried out from 1995 to 2007 in a wheat-cultivated area in Raddusa (Sicily, Italy), having a surface area of almost 80 ha, represent one of the longest series of field data on ephemeral gully (EG) erosion which permit analysis of the influence of precipitation on EG formation and development. Ephemeral gullies (both main branches and tributaries) formed in the study area were measured on a yearly scale with a PPD GPS for length and with a steel tape for the width and depth of transversal sections. Ephemeral gully formation was observed for eight years out of twelve, which corresponds to a return period of 1.5 years. The measurements show strong temporal variability in EG erosion, in agreement with the precipitation characteristics. The total eroded volumes ranged between 0 and ca. 800 m3 year-1, with a mean of ca. 420 m3 year-1 (corresponding to ca. 0.6 Kg m-2year-1). Ephemeral gully erosion in the study area is directly and mainly controlled by rainfall events. An antecedent precipitation index, the maximum value of 3-days cumulated precipitation (Hmax3_d), used as a simple surrogate for soil water content, is the rain parameter which best accounts for EG erosion in the environment considered. An Hmax3_d threshold of 51 mm was observed for EG formation. The return period of the Hmax3_d threshold is almost the same as the return period for EG formation. Although several erosive rain events were recorded in a year (a mean of seven), EG formation and development generally occur during a single erosive event, similarly to other semiarid environments. The most critical period is autumn or winter, when the soil is wetter and the vegetation cover is scarce. Simple empirical models for EG eroded volume estimation were obtained using the data set collected at this site. A simple power-type equation is proposed to estimate the eroded volumes using Hmax3_d as an independent variable.
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