One of the many factors that leads to soil erosion is rainfall erositivity, which is a basic physical factor enabling us to understand the geomorphological processes that take place in a basin. Results worldwide have shown that the erositivity R factor of the Universal Soil Loss Equation (USLE) has a high correlation with soil loss. In the past there have been few pluviometers capable of recording rainfall with continuous measurements. As a result of this lack of accuracy in the available series of rainfall intensity data, the calculation of the R factor has been restricted for a long time and various simplified models were developed on an international scale that relied on information obtained from existing stations. However, the modernisation of stations over the last few decades has provided to be a valuable tool for validating models, as well as for designing others that are more hardwearing and correlate better with the available information. In this paper, we have calculated the rainfall erositivity R factor for a semiarid basin in SE Spain using the formula developed in the USLE model for a series of 20 years of rainfall with 5-minute intervals, obtaining the mean R factor value of 620 MJ/ha∙mm/h per year and maximum values of up to 6000 MJ/ha∙mm/h per year. In addition, a comparative analysis of various simplified expressions was carried out to obtain the R factor. To obtain this value, we came up with a simplified equation based on annual maximum daily rainfall and average monthly rainfall, which resulted in a correlation coefficient of r = 0.936 and a P-value of 0.033 for the basin under study. Thus, from this structure of the equation we have compiled a series of parametric maps which enable us to calculate the R factor from any position within the basin under study.
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