Spatial distribution of vulnerable areas for gully erosion due to agricultural land abandonment in Southeast Spain

Abandonment of agricultural land is one of the main changes of land use in Mediterranean countries. From the land use change analysis with the CLUE-S model appeared that especially marl areas without irrigation possibilities are potentially subject to abandonment. However, specifically these areas are most vulnerable for gully erosion, due to dispersion and slaking of marl. The objective of our study was to test if gully erosion was more active on abandoned fields and to model the spatial distribution of potentially vulnerable areas. The study was carried out in the Carcavo basin, a semi-arid catchment in the province of Murcia (SE Spain). Abandoned and agricultural fields with similar topography and lithology were compared with respect to the number and activeness of gullies. At abandoned fields the number of gullies was two times larger than on agriculture fields, especially on abandoned terraced fields gully erosion was occurring frequently. With rainfall simulations the runoff characteristics were compared and this showed that runoff concentration occurred much quicker on the abandoned fields, as a result of crust formation and reduced storage capacity. The change of topsoil characteristics was confirmed by thin section analysis. With a simple GIS-model the potentially vulnerable areas for gully erosion were identified, based on topography, lithology, catchment size, and land use. These predictions enable researchers and engineers to mitigate gully erosion by applying preventive conservation practices.