MEDALUS soil erosion models for global change

Two novel soil erosion models have been developed within the MEDALUS projects. Their principal innovation lies in the explicit treatment of long-term interactions with the vegetation and soil, with implications for the way in which the surface flow and infiltration are described and distributed areally. The models are primarily targeted on and validated against Mediterranean landscapes for uncultivated conditions, but the conceptual principles have wider application. Both models contain four inter-related submodels for the atmosphere, vegetation, soil and surface subsystems, for a series of points down the length of a hillslope flow strip or catena. In the MEDALUS model, processes are represented in detail, and the model is designed to simulate outputs of water and sediment from the single catena, and the changes in this catena over time. A simplified version of the catena model is now being incorporated into the MEDRUSH model, in which subcatchments of 1–20 km2, each represented by a family of catenas, are combined, using water and sediment routing algorithms, to provide forecasts for catchments of up to 5000 km2. The paper emphasises three novel aspects of the models: first the long-term interactions and their scope for forecasting erosional soil degradation, second the way in which microtopography is treated within the models, and third the nesting of catenas and subcatchments within large catchments in MEDRUSH.