Decomposition of the effects on regional climate from recent historical
land cover changes in Europe
Abstract
Land cover changes (LCC) show biophysical effect on regional climate
because they modify the land surface albedo, evapotranspiration, and
surface roughness. Many previous studies focused on the effects of
individual land cover transitions, such as idealized large-scale
scenarios of deforestation/afforestation or historical forest clearance,
but the combined effects from the detected recent historical land cover
changes in Europe have not been explored. In this study, we use a
combination of a regional climate model (the Weather Research and
Forecasting model, WRF, v3.9.1) with a high resolution land cover data
to explore the effects on surface temperature of land cover changes
between 1992 and 2015. Previous studies use one unrealistic large-scale
simulation for each LCC to estimate its climate effects which present
large variations especially in mid-latitudes. Our analysis introduces a
new method simultaneously considering the effects of the mix of
historical land cover changes in Europe and the individual one
contribution. This approach, based on a ridge statistical regression,
does not require an explicit consideration of the different components
of the surface energy budget, and directly shows the temperature changes
from each land transition. Around 70 Mha of land transitions occurred in
Europe from 1992 to 2015. Approximately 25 Mha of agricultural land was
left abandoned, which was only partially compensated by cropland
expansion (about 20 Mha). Declines in agricultural land mostly occurred
in favor of forests (15 Mha) and urban settlements (8 Mha). Compared to
1992, we find that the land covers of 2015 are associated with an
average temperature cooling of -0.12±0.20 °C, with seasonal and spatial
variations. At a continental level, the mean cooling is mainly driven by
agriculture abandonment (cropland-to-forest transitions). Idealized
simulations where cropland transitions to other land classes are
excluded result in a mean warming of +0.10±0.19 °C, especially during
summer. Conversions to urban land always resulted in warming effects,
whereas the local temperature response to forest gains and losses shows
opposite signs from the western and central part of the domain (where
forests have cooling effects) to the eastern part (where forests are
associated to warming). Gradients in soil moisture and local climate
conditions are the main drivers of these differences. Our findings are a
first attempt to quantify the regional climate response to historical
LCC in Europe, and our method allows to unmix the temperature signal of
a grid cell to the underlying LCCs (i.e., temperature impact per land
transition). Further developing biophysical implications from LCCs for
their ultimate consideration in land use planning can improve synergies
for climate change adaptation and mitigation. Key words: land use/cover
change; regional climate mode; biophysical climate; EURO-CORDEX