Morfología Fluvial.-Tendencias en la erosividad de la lluvia (1955-2006) en la cuenca del Ebro

Abstract

RESUMEN Rainfall is one of the main factors affecting soil erosion. This effect is summarized in the concept of rainfall erosivity which involves the drop size distribution and kinetic energy of an event, its duration and intensity, and the runoff that generates. To calculate rainfall erosivity several indices can be applied. The most extensively used is the R factor of the Revised Universal Soil Loss Equation (RUSLE). To compute this index continuous rainfall data are needed. This kind of data is difficult to obtain with a good spatial and temporal coverage. In this work, daily rainfall records have been converted into daily rainfall erosivity data. For this objective, we used the Richardson et al. (1983) exponential relationship between rainfall volume and rainfall erosivity to create the Daily Rainfall Erosivity Model (DREM). The study has been carried out in 112 observatories in the Ebro Basin with rainfall data every 15 minutes (SAIH network) for the period 1997-2007. Results were satisfactorily validated with a set of validation statistics and goodness of fit between rainfall erosivity data series computed by the RUSLE procedure and the ones obtained by the exponential relationship. The DREM application to a longer daily rainfall data base (1955-2006) allowed creating the Daily Rainfall Erosivity Data Base which includes 156 observatories in the Ebro Basin. The second objective of this work was to analyze the temporal evolution of rainfall erosivity over the last 52 years. Results showed a decrease of rainfall erosivity in the majority of the area, being more intense in the east of the region. Monthly results showed clear spatial patterns with important implications for agriculture. Overall, the summer months experimented high increments in rainfall erosivity in the west of the region, were Atlantic influences generate more regular behaviour than in the Mediterranean side. These results will allow promoting soil conservation measures, in special in the months when soil is uncovered.