Impact of the new common agricultural policy of the EU on the runoff production and soil moisture content in a Mediterranean agricultural system

Soil moisture variability and the depth of water stored in the arable layer of the soil are important topics in agricultural research and rangeland management. In this study, we use the distributed rainfall-runoff (DR2) model to perform a detailed mapping of topsoil moisture status (SMS) in a mountain Mediterranean catchment. This model, previously tested in the same study area against the Palmer Z-index, is run at monthly scale for the current scenario of land uses and under three scenarios that combine the land abandonment and the application of the new common agricultural policy (CAP) of the European Union. Under the current conditions, runoff yield is scarce and presents a high spatial variability when monthly rainfall intensity and depth are low, and infiltration processes mainly lead to water storage in the soil. When rainfall intensity is high, runoff accumulation along the hillslopes controls the depth of available water in the soil, and SMS is more homogeneous. On average, scrublands and pasture have the wettest values, crops of winter cereal and abandoned fields have intermediate conditions, and areas of bare soil and forest have the driest conditions all the year around. The abandonment and no revegetation of the low productive fields located in steep areas and the collapse of their landscape linear elements (LLEs) produce not only an increase of 2.3 % of the overall SMS in the catchment in comparison with the current scenario but also an increment of the effective runoff that cross the cultivated areas of the lowlands and the runoff depth that reach the wetlands, increasing the soil erosion risk and compromising the conservation of the lakes. When the new green areas of the CAP are installed in the upper part of the fields of the lowlands and around the lakes, the runoff depth and thus siltation risk clearly decreases but also SMS decreases 1.7 and 1.1 % considering the current land uses and adding revegetation practices in the abandoned fields, respectively. Hence, a management scenario where: (1) abandoned fields are covered with a dense cover of shrubs, (2) the LLEs are preserved, (3) the green areas of the PAC are created, and (4) runoff harvesting practices are applied to partially compensate the water deficit, will help to preserve the humidity of the soil and will be of interest to keep the agricultural land use around the protected lakes of the study area.