MEDALUS SOIL-EROSION MODELS FOR GLOBAL CHANGE

Two novel soil erosion models have been developed within the MEDALUS p rojects. 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 vali dated against Mediterranean landscapes for uncultivated conditions, bu t the conceptual principles have wider application. Both models contai n four inter-related submodels for the atmosphere, vegetation, soil an d surface subsystems, for a series of points down the length of a hill slope flow strip or catena. In the MEDALUS model, processes are repres ented in detail, and the model is designed to simulate outputs of wate r and sediment from the single catena, and the changes in this catena over time. A simplified version of the catena model is now being incor porated into the MEDRUSH model, in which subcatchments of 1-20 km(2), each represented by a family of catenas, are combined, using water and sediment routing algorithms, to provide forecasts for catchments of u p to 5000 km(2). The paper emphasises three novel aspects of the model s: first the long-term interactions and their scope for forecasting er osional soil degradation, second the way in which microtopography is t reated within the models, and third the nesting of catenas and subcatc hments within large catchments in MEDRUSH. (C) 1998 Elsevier Science B .V. All rights reserved.