Hot spots of vegetation-climate feedbacks under future greenhouse forcing in Europe

We performed simulations of future biophysical vegetation"climate feedbacks with a regional Earth System Model, RCA"GUESS, interactively coupling a regional climate model and a process"based model of vegetation dynamics and biogeochemistry. Simulated variations in leaf area index and in the relative coverage of evergreen forest, deciduous forest, and open land vegetation in response to simulated climate influence atmospheric state via variations in albedo, surface roughness, and the partitioning of the land"atmosphere heat flux into latent and sensible components. The model was applied on a ∼50 × 50 km grid over Europe under a future climate scenario. Three potential "hot spots" of vegetation"climate feedbacks could be identified. In the Scandinavian Mountains, reduced albedo resulting from the snow"masking effect of forest expansion enhanced the winter warming trend. In central Europe, the stimulation of photosynthesis and plant growth by "CO2 fertilization" mitigated warming, through a negative evapotranspiration feedback associated with increased vegetation cover and leaf area index. In southern Europe, increased summer dryness restricted plant growth and survival, causing a positive warming feedback through reduced evapotranspiration. Our results suggest that vegetation"climate feedbacks over the European study area will be rather modest compared to the radiative forcing of increased global CO2 concentrations but may modify warming projections locally, regionally, and seasonally, compared with results from traditional "off"line" regional climate models lacking a representation of the relevant feedback mechanisms.