SIMULATION OF LAND-USE CHANGES AND IMPACTS ON THE WATER-BALANCE - A CASE-STUDY FOR BELGIUM

The impacts of assumed land use changes in the Houille catchment in Belgium are simulated by means of a conceptual hydrological model, developed at the Royal Meteorological Institute of Belgium. The largest difference in impacts appears between basin-wide coverage by coniferous forests and pastures. Indeed, the mean annual effective evapotranspiration is a maximum for 100% coniferous forests (552 mm year-1) and a minimum for pastures (477 mm year-1), while the mean annual streamflow is a minimum for coniferous forests (556 mm year-1), and a maximum for pastures (631 mm year-1). As compared with the pastures cover, the coniferous forests cover also demonstrates more frequent low-flow days (+14) and fewer flood days (- 10); the discharges associated with extreme flood and low-flow conditions are however almost unaffected. Intermediate results are found for the other vegetation types. A simplified method for assessing the impacts of limited or complex changes of vegetation is proposed. The enlargement of impervious areas clearly modifies the streamflow regime in the basin by inducing more floods as well as longer low-flow stages. © 1990.