Methodology of land cover datasets for global and regional climate models

The different model approaches within OptFor-EU are associated with different requirements on the representation of land cover. The two RCMs, REMO2020iMOVE and RegCM, conduct coordinated simulations. The first set of RCM simulations is conducted for the European continent covering all CSAs and using the new dataset LUCAS LUC developed by Hoffmann et al. 2023. These experiments include transient LULCC at 0.11° horizontal resolution. After evaluation experiments, which assess the uncertainty of our models using reanalysis forcing, we conduct experiments for the historical period (1950 – 2014) and for the SSP126 scenario (2015 - 2100) implying strong afforestation. In order to represent the FMP thinning, we will conduct a second set of RCM simulations for selected CSAs on convection-permitting scale at 0.0275° (~3 km) horizontal resolution. For this set of simulations, a high-resolution dataset with an implemented thinning procedure had to be developed. In this deliverable we describe the development of a new land cover dataset, that includes thinning for both selected CSAs: CSA4 (Eastern Lowlands in Lower Saxony) and CSA6 (Arges and Teleorman county). We use the LANDMATE dataset at 0.018° horizontal resolution as basis and, as first step, interpolated it to our target resolution of 0.0275°. As second step, we implemented thinning with a changed tree-grass-proportion in the grid cells. We take advantage of the different model approaches in OptFor-EU and link our assumptions to the experiments conducted by the forest models in D2.2 Report on new Forest Management Practices (FMP) in forest models and implications for land cover change parametrisation in climate models (Neumann et al. 2024b) under the BAU procedures. The dataset is publicly available for the two selected CSAs. For addressing different coordinate systems or additional CSAs, the source code for the dataset creation is published with the data (Pop et al. 2024). The new data will be implemented in both RCMs and simulations for both CSAs will be performed with and without the FMP thinning. The effects of changes in forest-grass proportions on land surface characteristics and land-atmosphere exchange processes will be examined, along with further impacts and feedback on the atmosphere and climatic patterns. Here, we will focus mainly on regional climate regulating variables selected in D1.2 Report on a novel set of Essential Forest Mitigation Indicators (EFMIs), including indicator factsheets with open-access code (Linser et al., in prep.): temperature, precipitation, soil moisture, evapotranspiration, water vapour content and runoff. For more information, please visit the project website: https://optforeu.eu/