Work

What drives gullies in Spain’s olive landscapes? A regional analysis of gully activity

Year: 2025

Type: article

Abstract: Gully erosion poses a significant threat to Mediterranean basins. However, precise spatial data on gullies location at regional scale is scarce. Current models often use the topographic threshold index, TT, which works locally and predicts gully location based on slope and drainage area but does not distinguish between actively retreating gullies and stabilized gullies. We aim to close this gap by (i) constructing a dataset of gully location and activity in olive groves in southern Spain across different landscape regions and (ii) evaluate a process-oriented model to distinguish gully presence and activity based on the Gully Head Initiation (GHI) index (De Geeter et al., in review). This GHI integrates slope, drainage area, precipitation, curve number (CN), soil type, and clay content to predict gully formation. Based on photointerpretation of four 25 km2 study areas between 2008 and 2019, 3 gully activity classes were identified, and found 261 actively retreating gullies, 76 newly formed gullies and 138 stable gullies. The GHI clearly distinguishes between gully and non-gully pixels, with area under the curve (AUC) value of 0,93. It also differentiated active from stable gullies and newly formed from active ones. However, there are no significant differences between stable and newly formed gullies. Besides, applying the model separately by landscape type is not as effective as applying it to all landscapes together. These results highlight the potential applicability of GHI at the regional scale and confirm that the factors considered in the GHI index affect both gully initiation processes and erosion dynamics.

Source: CATENA

DOI: 10.1016/j.catena.2025.109699

Authors: Paula González, Adolfo Peña, Sofie De Geeter, Matthias Vanmaercke, Jean Poesen, Tom Vanwalleghem