Curve number values for olive orchards under different soil management

The Soil Conservation Service curve number methodology (SCS-CN) has been used in hydrological and crop models to evaluate the effects of soil management in olive (Olea europaea L. subsp. europaea) orchards on runoff, erosion, and water balance. To our knowledge, it has never been calibrated or validated for olive orchards. A physically based runoff model for olive orchards at a hillslope scale was used to generate rainfall-runoff relationships for different scenarios of soil type (four), tree size (two), tree spacing (two), antecedent soil moisture (three), and soil management (11) for a 140-m-long and 5% steep hillslope. The resulting relationships were used to derive the values of the curve number parameter, CNd, for the SCS-CN methodology. The resulting CNd values were validated using rainfall-runoff data for three different locations and different soil management. Predictions of daily runoff using CNd were compared with those made using CN values extracted from the standard SCS-CN tables, CNSCS. The derived CNd values presented a root mean square error in runoff predictions between 0.5 and 7.3 mm, and a model efficiency between 82 and 97%. The extracted CNSCS values presented a root mean square error in runoff predictions between 1.4 and 10.4 mm, and a model efficiency between -81 and 89%. Our analysis identified some issues in the hydrology of olive orchards where our understanding remains limited. Among them are the need for further validation of the derived CN values given the limited rainfall-runoff data, and the effect of soil management on soil properties and their temporal evolution.