Evaluating the Respective Impact of the Radiative Forcing and Fertilization Response of Vegetation to a Carbon Dioxide Enriched Atmosphere during Severe Heatwaves in Western Europe

Abstract:

In a CO2 enriched atmosphere, vegetation-land-atmosphere interactions can change the intensity of extreme meteorological episodes like heatwaves, alter the timing of occurrence and modify the way they evolve. We propose to focus on the 2003 heatwave in Western Europe. How this extreme meteorological event would be different under CO2 atmospheric concentration expected for 2100?

To investigate this question, we couple an atmospheric model (WRF) to a surface model (ORCHIDEE). Both models use atmospheric CO2 concentration as an input parameter; both can have different CO2 concentrations without producing any conflict. Four simulations have been designed and run in order to quantify and understand the impact of the radiative forcing and the response of the vegetation to CO2 fertilization. Based on the actual recorded meteorology, a first simulation is performed with today’s CO2 concentration applied to both the atmospheric and surface models, defined as the control run (CTL). A second simulation is run with the 2100 CO2 concentration applied to the atmospheric model only (impacting radiation), the surface model being run with today’s conditions. This way we can evaluate the impact of the radiative forcing (RAD). In a third simulation, the surface model is run with the 2100 atmospheric CO2 concentration, while the today’s conditions are applied to the atmospheric model. This run enables us to quantify the response of the vegetation fertilization (and change in water use efficiency) in a CO2 enriched atmosphere (PHOT). A last simulation is achieved with 2100 conditions applied to both the atmospheric and surface models (FUT).

 We measure opposite effects on the surface temperature from the radiative forcing (warming effect) and from the vegetation response (cooling effect), even if in both cases the effect stays relatively small. Both effects partly compensate each other in future conditions simulation (see Figure 1). None of the investigated feedback overtakes the other one. Latent heat seems to play a key role.