| Abstract: | A hydrological conceptual model developed by the Royal Meteorological Institute of Belgium has been run to assess the potential hydrological impacts of an hypothetical doubling of the atmospheric CO2 concentration. The simulated scenarios were derived from the predictions of climatic change currently provided by General Circulation Models (GCMs). Three typical drainage basins in Belgium have been selected for assessing their common responses and bringing out possible specific behaviours attributable to catchment characteristics. The study dealt essentially with modifications of the streamflow and with alterations of the flood and low-flow regimes. In catchments with prevailing surface flow the considered change in climate could induce: - An increase in flood frequencies during the winter season together with a strengthening of the extreme river stages leading to greater flooding risks;
- A decrease in streamflow during the summer season and, as a corollary, increased risks of water pollution;
- Possible restraints, in summer and autumn, on water availability from local groundwater storages.
In catchments with high infiltration rate and with strong aquifer the impact could be: - An increase in groundwater storage, bringing about an increase in the base flow throughout the year, which in turn involves increased flood risks;
- A reduction of the number of low-stage occurrences in summer, resulting in reduced river pollution;
- A possible increase in water availability from the aquifers.
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