Vertic soils are common in Mediterranean areas, such as in some olive-growing areas in Andalusia in southern Spain. Model calibration can be especially complex in orchards due to the higher spatial variability induced by the tree/lane distribution and the impact of management, and even more in Vertic soils because of the complexity introduced by the cracking/swelling cycles of the soil, whose impact can remain for many months. The WEPP model was evaluated using monthly runoff and erosion data collected from an experiment in an olive orchard on a Vertic soil during four hydrological years, comparing three different soil management systems: no tillage with bare soil (NT), conventional tillage (CT), and cover crop (CC). These three systems differed greatly in average annual runoff and soil losses. Satisfactory calibration of the model required characterization of the main hydrological features of the study period (distinguishing "dry" and "wet" years) due to their large impact on the infiltration properties of the soil. The best predictions were obtained for the wet years and NT management. High values of r2 and Nash-Sutcliffe model efficiency (NSE) were obtained at a monthly scale under wet conditions. Annual erosion rates were not well predicted, probably due to the difficulties in simulating the spatial complexity of olive orchards and the limitations of WEPP for modeling soil moisture dynamics at different depths derived from the cracking/swelling processes of Vertic soils as well as their impact on erodibility. The presented parameterization constitutes a basic guideline for the application of the WEPP model in olive-growing areas and on Vertic soils. © 2013 American Society of Agricultural and Biological Engineers.

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