Simulating the effect of anthropogenic vegetation land cover on heatwave temperatures over central France

Events similar to the 2003 heatwaves in France are likely to become more frequent, more intense and longer by the end of the 21st century. Policies for climate mitigation focus on carbon sequestration techniques while land cover change (LCC) may be a better short-term alternative at regional level. However, LCC impact studies conducted so far have often given contradictory results at mid-latitudes for summer temperature. Using a regional climate model, the impact of an afforestation scenario is evaluated for the years 2002 and 2003, and compared to an agricultural scenario. The favorable meteorological conditions in spring 2003 promote the development of agricultural vegetation compared to (1) conditions in 2002 and (2) tree phenology in the forested scenario. This dampens the extreme values of temperature from April to the end of June 2003 (up to 3°C during the June heatwave). From early July to October, drought conditions cause crop failure, while forests are not affected by the lack of soil moisture owing to a deeper root system. Eva - po transpiration is therefore smaller in the agricultural scenario, thus amplifying the July-August extreme temperatures. However this cooling capacity of trees in the afforestation scenario is limited during the August heatwave because the high temperatures reach a critical level above which the stomata close and transpiration is inhibited. Our experimental set-up highlights the role of climate-vegetation interactions during extreme events and demonstrates how choices of vegetation cover (e.g. trees versus crops) may substantially modify the summer temperatures in mid-latitude regions.