Modelling the Impact of Soil Water Repellency on Catchment-Scale Soil Erosion

Soil erosion is a significant environmental issue with far-reaching consequences for both agriculture and the natural ecosystem. Soil water repellency (SWR) impacts erosion through a dual mechanism. Hydrologically, SWR reduces infiltration and enhances overland flow, intensifying erosion. Mechanically, it affects soil cohesion, potentially decreasing resistance to detachment. While the hydrological effects are well studied, the mechanical impacts of SWR remain less explored. Previous studies have reported mixed impacts of SWR on soil erosion, with SWR sometimes increasing soil erosion and, in other cases, reducing it. To address this apparent ambiguity, we use catchment-scale simulations with the LISEM model to systematically isolate and test SWR’s hydrological effects (via reduced infiltration) and mechanical effects (via altered soil cohesion) on erosion. Two types of configurations are considered: spatially homogeneous (uniform land cover and soil type) and heterogeneous (spatially varied SWR, based on land cover or soil type). All configurations are run under two regimes: low- and high-excess rainfall. Considering only the hydrological impacts was found to consistently increase erosion in all configurations. In homogeneous setups, changes in soil cohesion produce texture-dependent responses: increased soil cohesion mitigates erosion increases in finer soils but has a limited impact in coarse-textured soils. This effect is much more pronounced under high-excess rainfall than low-excess rainfall. The heterogeneous configuration exhibits distinct spatial patterns: land cover–based heterogeneity follows vegetation-slope interactions, whereas soil-based heterogeneity is shaped by intrinsic soil hydraulic–-mechanical properties. Overall, the net erosional impacts of SWR are shown to depend on the balance between its hydrological and mechanical effects on erosion. This research implies that preventing and mitigating the erosional impacts of SWR requires a management approach adapted to the prevailing land-use and soil conditions.