Impact du changement climatique à l'échelle du kilomètre en Europe

The main objectives of the km-impacts project consisted to quantify the impacts of climate change on floods, urban climate and coastal meteorological processes of Mediterranean islands by taking advantage of a new generation of regional climate models (RCMs) that use fine spatial resolutions of the order of 2 km. With such high horizontal resolutions, these RCMs have the major advantage to simulate explicitly deep convection that was before computed with parameterizations, a major source of uncertainty known to affect climate change projections. The RCM used in this project is the CNRM-AROME model that is developed at the Centre National de Recherches Météorologiques (CNRM) of Météo-France.

The first part of the project was dedicated on a review paper of the quickly growing literature of high-resolution RCMs and on a comprehensive evaluation of the high-resolution RCM (CNRM-AROME) developed at the CNRM. The evaluation focused on the comparison of a 2.5-km CNRM-AROME simulation with its driving 12-km CNRM-ALADIN simulation over a large northwestern European domain. To analyze the ability of CNRM-AROME to simulate hourly precipitation, high-resolution national radar and weather station precipitation datasets from different countries were interpolated on a common grid. Overall, the evaluation indicated that CNRM-AROME is a suitable high-resolution RCM that is superior in many aspects to the CNRM-ALADIN RCM.

During this project, three PhD students completed their thesis. The first thesis by Yohanna Michau highlighted the ability of CNRM-AROME to simulate the urban heat island effect and analyzed the impacts of climate change on heatwaves for 12 cities in France projected by several high-resolution RCMs. The second thesis by Nils Poncet revealed that high-resolution RCMs can improve the simulation of Mediterranean floods and that the projections of these floods can differ significantly from those using conventional RCMs. The third thesis by Virginia Edith Cortes Hernandez underlined that high-resolution RCMs improve the simulation of small-scale coastal meteorological processes (sea breezes and orographic precipitation) occurring over Corsica Island and that precipitation extremes are expected to increase more in the future using high-resolution RCMs compared to conventional ones.