Considering spatial distribution and functionality of forests in a modeling framework for river basin management

This paper emphasizes the need of an improved consideration of the spatial distribution and functionality of forests in river basin management. The review of relevant papers has shown that forests, despite their frequent occurrence in temperate zones, play presently only a minor role in river basin management. In general, most of the studies highlight the positive effect of forests on water and nutrient fluxes in river basins. But hydrologists have also reported consistently flood events in or originating from forested areas. In context of the discussion on forest ecology and water quality it became obvious, that forest ecosystems can be sources depending on system properties, time and atmogenic pollution.The simulation of land use changes on water yield in forested river basins has been carried out in a great number of research projects, but mostly without considering the spatial distributed function of forests. The objective of our work is thus to improve the consideration of spatial distribution of forests in river basins and its effect on water yield and water quality. The most promising approaches in the future are either spatial explicit models or integrated models with both improved forest modules and landscape positioning. The efficiency of these models could be proved by using virtual catchments. As a first conceptual approach towards the base concept of a virtual catchment, we propose a five-units-model (FUM), representing cross-sections with typical land use sequences. The basic idea of our model is to identify major process units and to implement them in the river basin modeling and management.