Testing the long term applicability of USLE-M equation at a olive orchard microcatchment in Spain

Universal Soil Loss Equation USLE-based erosion models have been used extensively to complement erosion measurements, to understand the interactions of the different geophysical features into erosion processes and to assess adequate alternative management practices and scenarios analyses. Despite its proved usefulness on different land-uses around the world, there is an urgent need to set up simple tools which do not require an advanced management expertise in terms of both choose of model parameters and calculation ability and which are accurate particularly at the event scale. In this paper the suitability of the Modified USLE (USLE-M) model at the event and the annual scale were evaluated in an olive orchard catchment of 6.1 ha in Spain where a rainfall-runoff-sediment yield dataseries of over 8 years (2005-2013) was available. The model was applied dividing the catchment into morphological units, i.e. areas having a defined aspect, length and steepness. In addition, different model parameterizations of both the crop factor of the Revised USLE factor and β-coefficient of the sediment delivery ratio of each morphological unit were studied in order to describe the seasonal variability of soil conditions along the year. At event scale the best performance of the USLE-M model was obtained using a single value of the b coefficient equal to median value be,m without considering the seasonal variability of crop factor since it is well-represented by the term rainfall-runoff erosivity index. At the annual scale, the calculation of crop factor values provided a good model performance in estimating sediment yield, with a coefficient of efficiency of 0.96. The analysis demonstrated that the USLE-M model was a useful tool to simulate soil losses at the event and annual scales and its application might provide guidelines for other users.