Characterization of raindrop size distributions at the Vale Formoso Experimental Erosion Center

Previous studies carried out by the authors and other references collected from the literature have shown the inadequacy of most rainfall erosivity indexes and specially the Wischmeier rainfall erosivity index, for properly estimating erosivity in southern Portugal and in Mediterranean climates. In order to measure raindrop size distributions of natural rainfall automatically and continuously, a device was installed at the Vale Formoso Experimental Erosion Center. The main objective was to correlate field measurements to model estimates. The relatively small amounts of rain which fell at the station last year meant that it was only possible to check the calibration of the device; preliminary results are presented here. Classical raindrop distributions are compared with the data and relationships between rainfall intensity and kinetic energy of rainfall are obtained and compared with that proposed by RUSLE.