Browsing by Person "Breil, Marcus"

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The effect of forest cover changes on the regional climate conditions in Europe during the period 1986–2015
(2024) Breil, Marcus; Schneider, Vanessa K. M.; Pinto, Joaquim G.
Afforestation affects the earth's 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 midlatitudes is still the 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 strongly, 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 -1.9 K. In winter, afforestation results in a slight local warming in both 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 the 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.
Extrapolation is not enough: impacts of extreme land use change on wind profiles and wind energy according to regional climate models
(2024) Wohland, Jan; Hoffmann, Peter; Lima, Daniela C. A.; Breil, Marcus; Asselin, Olivier; Rechid, Diana; Wohland, Jan; Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland; Hoffmann, Peter; Climate Service Center Germany (GERICS), Helmholtz-Zentrum Hereon, Hamburg, Germany; Lima, Daniela C. A.; Universidade de Lisboa, Faculdade de Ciências, Instituto Dom Luiz, Lisbon, Portugal; Breil, Marcus; Institute of Physics and Meteorology, University of Hohenheim, Stuttgart, Germany; Asselin, Olivier; Ouranos, Montréal, Canada; Rechid, Diana; Climate Service Center Germany (GERICS), Helmholtz-Zentrum Hereon, Hamburg, Germany
Humans change climate in many ways. In addition to greenhouse gases, climate models must therefore incorporate a range of other forcings, such as land use change. While studies typically investigate the joint effects of all forcings, here we isolate the impact of afforestation and deforestation on winds in the lowermost 350 m of the atmosphere to assess the relevance of land use change for large-scale wind energy assessments. We use vertically resolved sub-daily output from two regional climate models instead of extrapolating near-surface winds with simplified profiles. Comparing two extreme scenarios, we report that afforestation reduces wind speeds by more than 1 m s −1 in many locations across Europe, even 300 m above ground, underscoring its relevance at hub heights of current and future wind turbines. We show that standard extrapolation with modified parameters approximates long-term means well but fails to capture essential spatio-temporal details, such as changes in the daily cycle, and it is thus insufficient to estimate wind energy potentials. Using adjacent climate model levels to account for spatio-temporal wind profile complexity, we report that wind energy capacity factors are strongly impacted by afforestation and deforestation: they differ by more than 0.1 in absolute terms and up to 50 % in relative terms. Our results confirm earlier studies showing that land use change impacts on wind energy can be severe and that they are generally misrepresented with common extrapolation techniques.