Abstract
Previous studies based on observations and models are uncertain about the biophysical impact of af- and deforestation in the northern hemisphere mid-latitude summers, and show either a cooling or warming. The magnitude and direction is still uncertain. In this study, the effect of three different albedo parameterizations in the regional climate model COSMO-CLM (v5.09) is examined performing afforestation experiments at 0.44° horizontal resolution across the EURO-CORDEX domain during 1986-2015. Idealized de- and af-forestation simulations are compared to a simulation with no land cover change. Emphasis is put on the impact of changes in radiation and turbulent fluxes. A clear latitudinal pattern is found, which results partly due to the strong land cover conversion from forest- to grassland in the high latitudes and open land to forest conversion in mid-latitudes. Afforestation warms the climate in winter, and strongest in mid-latitudes. Results are indifferent in summer owing to opposing albedo and evapotranspiration effects of comparable size but different sign. Thus, the net effect is small for summer. Depending on the albedo parameterization in the model, the temperature effect can turn from cooling to warming in mid-latitude summers. The summer warming due to deforestation to grassland is up to 3 °C higher than due to afforestation. The cooling by grass or warming by forest is in magnitude comparable and small in winter. The strength of the described near-surface temperature changes depends on the magnitude of the individual biophysical changes in the specific background climate conditions of the region. Thus, the albedo parameterization need to account for different vegetation types. Furthermore, we found that, depending on the region, the land use change effect is more important than the model uncertainty due to albedo parameterization. This is important information for model development.
Highlights
Future strategies for climate change mitigation envision extensive afforestation to stabilize temperature rise due to their role in the global carbon cycle (Popp et al, 2017)
The effect of three different albedo parameterizations is examined for afforestation experiments at 0.44◦ horizontal resolution across the EURO-CORDEX domain during 1986-2015
Idealized de- and af-forestation simulations are compared to the simulation with no land cover change
Summary
Future strategies for climate change mitigation envision extensive afforestation to stabilize temperature rise due to their role in the global carbon cycle (Popp et al, 2017). Forest cover changes exert strong influences on the energy and water balance by modifying the solar and long wave radiation, and atmospheric turbulence. This results in alterations in the fluxes of momentum, heat, water vapor, and CO2 as well as other trace gases, and both anorganic and biogenic aerosols including dust between vegetation, soils, and the atmosphere (Pielke et al, 2011). The outcome of the competition between albedo warming and evapotranspiration cooling, and the specific background climate exerts the climate of the region (Duveiller et al, 2018) The strength of both effects, the direction of change, depend on the type of change, and on the interactions with soil conditions (Pielke et al, 2011). Landscape changes due to forests affect the regional/local near-surface air temperature patterns (Tölle et al, 2014), and can be different for mean vs. extreme quantities (Alkama and Cescatti, 2016)
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