One of the best indicators of the potential erosion risks is the rainfall-runoff erosivity factor (R) of the revised universal soil loss equation (RUSLE). Frequently, however, there is not enough data available to compute the R value, and other parameters, such as the modified Fournier index (F m o d ), are used instead. But RUSLE is less effective if only the alternative procedures exist. One of the major discrepancies between R and the alternative parameters is time resolution: individual storms are used to calculate R while monthly averages over the year are used to calculate F m o d .In this study, a multiple linear regression (r 2 =0.89) involving monthly EI 3 0 , monthly rainfall for days with =<10.0mm and monthly number of days with rainfall =<10.0mm, for the Algarve region, is presented. Twenty-seven years of monthly rainfall erosivity values were computed for the 32 standard daily-read raingauge stations of the Algarve region.