Curve Numbers for Olive Orchard Catchments: Case Study in Southern Spain

The curve number (CN) method is widely applied around the world to estimate direct runoff and the corresponding hydrograph of a rainfall event. However, there is no information on its performance in olive orchards on the catchment scale. In this work, the CN method was applied in three small catchments in southern Spain with different soil types, topography, and management. A rainfall-runoff data set of six years was used to test the usefulness of the method and the accuracy of its reference parameterization (CNs) and of the initial abstraction (Ia). CN medians in the catchments were between 83 and 87. Classical equations based on the use of the 10th, 50th, and 90th CN percentiles for determining the antecedent moisture content (AMC) provided very good results in two of the catchments. In the third catchment, with the most arid hydrological pattern (annual rainfall <400  mm) and the most impervious areas of parental material, very poor performance was achieved. In addition, cumulative precipitation was not a good indicator of AMC. Finally, significant deviations were observed in reference CNs for sandy soils that should be treated with caution for hydrological planning. They illustrate the need for new studies evaluating the hydrological behavior of olive orchard catchments with different environmental features and management practice.