What will be the impacts of climate change on surface hydrology in France by 2070?

Within the Explore 2070 project, an evaluation of the possible impacts of climate change on surface water between the 1961-1990 reference period and the 2046-2065 period was carried out in continental France and i n overseas departments on the basis of the A1B greenhouse gas emission scenario, seven general circulation models an d two hydrological models (Isba-Modcou and GR4J). In continental France, results indicate: (1) a possible increase in ai r temperature between +1.4 deg. C and +3 deg. C; (2) an uncertain evolution of precipitation, most models however agreeing on a decreasing trend in summer precipitation; (3) a significant decrease (10% to 40%) of mean annual flows at the country scale, especially pronounced in the Seine-Normandie and Adour-Garonne districts; (4) a strong decrease in summer lo w flows in most basins; (5) more heterogeneous and less significant evolutions for floods. A special care was given to the quantification of the uncertainties linked to these results. They provide an indication of the significance of projected changes. The evolutions calculated in the overseas zones can be considered non-significant given the level of uncertainty linked to the hydro-climatic modelling chain. These results urge to implement adaptation strategies based on a better management of water resources, among others. (authors)