Impact of vegetation cover on hydro-sedimentary fluxes in the marly badlands of the Southern Alps (Draix-Bléone Critical Zone Observatory, SE France)

Abstract

Located in the Southern Alps, the Terres Noires region is characterized by highly erodible and poorly permeable soils. This, combined with the steep slopes and short, intense rains of the Mediterranean climate results in the formation of highly rilled/gullied surfaces known as badlands. Anthropogenic activities such as deforestation have exacerbated runoff and erosion on these surfaces. The aim of this study is to characterize the influence of vegetation cover on the multiscale temporal hydro-sedimentary functioning (and its controlling factors) of badlands. For this purpose, an approach combining the analysis of field data and the use of the physics-based model CAESAR-Lisflood was developed. The results indicate that the forested surfaces exhibit greater dampening of the fluxes than the bare surfaces, especially in the short term. The lower hydrological reactivity of the forested areas compared to the bare areas can be attributed to the higher retention and percolation capacity of the forested soils. Additionally, vegetation impedes the formation of regolith and the physical disaggregation of particles by regulating humidity and temperature fluctuations. With regard to predictive capacity, the model provides reliable estimates of the hydrologic balance of the catchments. However, there is potential for improvement in the calibration process to better represent the temporal dynamics of water flows and the amplitude and variability of sediment fluxes. The results of this study can serve as a basis for the development of water and soil management strategies in the badlands of the Southern Alps.