The effect of forest cover changes on the regional climate conditions in Europe during the period 1986-2015

Afforestation affects the earths climate system by changing the biogeochemical and biogeophysical characteristics of the land surface. While the regional effects of afforestation are well understood in the tropics and the high-latitudes, its climate impact on the mid-latitudes is still subject of scientific discussions. The general impact of afforestation on the regional climate conditions in Europe during the last decades is investigated in this study. For this purpose, regional climate simulations are performed with different forest cover fractions over Europe. In a first simulation, afforestation in Europe is considered, while this is not the case for a second simulation. We focus on the years 1986-2015, a period in which the forest cover in Europe increased comparatively strong, accompanied by a strong general warming over the continent. Results show that afforestation has both local and non-local effects on the regional climate system in Europe. Due to an increased transport of turbulent heat (latent + sensible) into the atmosphere, afforestation leads to a significant reduction of the mean local surface temperatures in summer. In northern Europe, mean local surface temperatures were reduced about -0.3 K with afforestation, in central Europe about -0.5 K and in southern Europe about -0.8 K. During heat periods, this local cooling effect can reach to -1.9 K. In winter, afforestation results in a slight local warming both in northern and southern Europe, because of the albedo effect of forests. However, this effect is rather small and the mean temperature changes are not significant. In downwind direction, locally increased evapotranspiration rates with afforestation increase the general cloud cover, which results in a slight non-local warming in winter in several regions of Europe, particularly during cold spells. Thus, afforestation had a discernible impact on the climate change signal in Europe during the period 1986-2015, which may have mitigated the general warming trend in Europe, especially on the local scale in summer.