Changement climatique et événements extrêmes : crues, inondations, sécheresses. Que peut-on dire aujourd’hui ?

Abstract

Will climate change lead to more floods and droughts? This paper presents an analysis of stationarity performed on an extended data set of time series from two hundred French gauging stations. This study involves the cautious selection of statistical tests to be carried out and a meticulous quality control of data to avoid drawing biased conclusions. Results do not provide any evidence of a generalized and consistent change at the scale of France during the last century. However, some consistent trends emerge at the regional scale: a weak increase of floods is detected in the North-East of France, whereas droughts seem more severe in the Pyrenean area and less extreme in the Alps. However Global Circulation Models (GCMs) forecast major evolutions of temperatures and significant, although contrasted, evolutions of rainfall. The balance between rainfall and evapotranspiration will therefore be strongly affected. Hydrologic rainfall-runoff models predict more severe droughts in French rivers, mainly in the South of France. A more accurate assessment of climate change impacts on hydrological extremes is unfortunately impossible, notably because of scale inconsistencies between GCM and hydrological models. However cautiousness suggests that such evolutions cannot be disregarded even if available numerical tools are unable to calculate reliable numerical values.