Identification of vulnerable areas for gully erosion under different scenarios of land abandonment in Southeast Spain

Abandonment of agricultural land is the result of interacting processes of global change and human behaviour. Due to changing European policies, urbanisation, desertification and climate change land abandonment has become one of the main changes in land use in Mediterranean countries. The consequences of land abandonment depend on environmental, agricultural and socio-economic contextual factors, but generally have an undesirable environmental effect. One of these consequences is land degradation and gully erosion in specific. In semi-arid areas gully erosion increases after land abandonment because runoff concentration occurs much quicker due to the very slow vegetation cover recovery, crust formation and reduced surface storage capacity, as well as the lacking land management. To mitigate runoff and erosion from abandoned land, it is necessary to identify locations where water concentrates, and that are vulnerable to erosion as result of land abandonment.

The objective of this study was to identify the vulnerable areas for gully erosion in relation to land abandonment. This research is part of the RECONDES project, which focuses on the mitigation of desertification processes by means of innovative techniques using vegetation in specific landscape configurations prone to severe degradation processes. The study area was the Carcavo basin, a semi-arid catchment in Southeast Spain. The spatial dynamics of land abandonment were simulated with the spatially-explicit land use change model CLUE-s. Four different land use change scenarios were derived from the MedAction scenarios for the period 2004 to 2015. The results of the simulations were used to identify vulnerable areas for gully erosion by a GIS-model based on the controlling factors of gully erosion, which are topography, land use and soil type.

The potentially vulnerable areas for gully erosion increased for the different scenarios ranging from 18 ha to 176 ha. Most of the vulnerable areas are located around channel heads or along channel walls, which are critical positions at the transition of the hillslope to the channel. This means that when a gully becomes active the connectivity of runoff and sediment in the landscape increases considerably. The combination of more gully erosion on abandoned fields and an expected increase of land abandonment is potentially a big problem in relation to land degradation, flash flood generation and reservoir sedimentation. However, identification of vulnerable areas enables soil and water conservationists and engineers to mitigate runoff concentration and gully erosion by applying preventive sustainable conservation practices.