A set of 874 erosive individual rainfall occurrences was selected from a continuous serie of twenty-three years of recording rain gauge data. All the selected rainfall occurrences were analized. The rainfall erosivity factor computed was 7074 MJ mm ha-1 h-1 y-1, which is expected to occur at least once every 2.33 years, with a probability of occurrence of 42.92%. The values of the annual erosivity indexes at that site expected for the return periods of 2, 5, 10, 20, 50, and 100 years, were respectively 6,696, 8,730, 10,076, 11,367, 13,039, and 14,292 MJ mm ha-1 h-1 y-1. The most annual soil loss is expected to ocour between the months of October and March (78.5%) where 46.9% occurs between december and february of the total annual erosivity for that period, in whose periods is expected high erosion soil loss. A high correlation was found between the montly average erosivity index EI30 and the rainfall coefficient at that site. Therefore, the regression equation obtained allows a fair estimative of the R factor to be used for other regions where climatic conditions are similar to Piraju's and where there are no available data.
R factor; soil erosion; universal soil loss equation; erosivity