Hydrological and erosion response of a badlands system in semiarid SE Spain

A long term monitoring program is being conducted to study runoff and erosion processes in a semiarid badlands environment (Tabernas Desert, SE Spain). The first six years of data from an instrumented experimental area with nested microcatchments are presented. The overall area is composed of a complex mosaic of soil surfaces with contrast hydrological and erosion behaviour. At microcatchment scale, runoff and erosion are controlled by the types of soil surfaces: small bare microcatchments had the highest runoff coefficients and the highest erosion rates, while those completely covered by vegetation had the lowest. Rainfall intensity significantly affected water and sediment budgets. The effect of antecedent soil moisture could only be observed when soil was near saturation and a few millimetres of additional rainfall were sufficient to produce Horton-type runoff, but it was very difficult to separate this from the effect of surface crusts formed in the first minutes of rainfall. Most of the rainfall events were below the threshold for producing runoff although they were important for sediment preparation through weathering. Small magnitude, low-intensity rainfall events along with protective plant cover over half of the total surface, are the main factors explaining low overall erosion rates at microcatchment scale.