Bridging the Gap Between Policy-Driven Land Use Changes and Regional Climate Projections

Changes in the land surface interact with a changing climate. Moreover, the impact of land surface changes on the local and regional climate can be as large as the impact of increasing greenhouse gas emissions. The land surface-climate interactions are best represented by high-resolution models to capture the mesoscale circulation features. The future land surface changes are preferably represented by scenarios that illustrate plausible storylines. Furthermore, the impact of future urbanization is relevant for the highly urbanized region of Europe. In this study, we assess the interactions between climate and land surface dynamics by modeling the near-future climate state for western Europe based on a policy-driven land use change scenario at high resolution. The global climate model CNRM-CM5.1 has been downscaled to the regional climate of western Europe by using ALARO-SURFEX at 4-km horizontal resolution. SURFEX provides a parameterization of the urban physical properties so that the impact of urban surfaces on the regional climate can be modeled realistically. Results are interpreted with respect to the near-future climate change without land surface changes. The near future presents a uniform temperature increase of 0.3-0.6 degrees C. This is in contrast to changes by the land surface that are more heterogeneous in space and much stronger at the local scale. Deforestation and conversion to arable land diminishes climate change effects, whereas urbanization results in an enhancing effect of climate change. Moreover, urbanization is as big as the radiative forcing warming for minimum temperature.