eLTER PLUS Deliverable D9.3 - A report detailing the pan-European continental scale terrestrial ecosystem model

In this deliverable, we describe the setup of a terrestrial ecosystem model, the Community Land Model 5 (CLM5), over continental Europe in the framework of the eLTER RI. For this setup, we first create input data of atmospheric conditions and static land surface information in 3 km resolution and conduct a long-term carbon cycle spin-up for adequate initial conditions of the carbon pools. Then, we evaluate our model results by comparing in-situ observations from eLTER with model data and identify caveats by analyzing the scale differences and data processing methods. To evaluate the simulated ecosystem processes from the European CLM5, we leverage the co-location with data on energy, water, and carbon fluxes from the ICOS RI spanning the whole station network on the continent and the years 1995 to 2018. The evaluation includes the grid level and the plant functional type (PFT) level of CLM5 data. We find that the CLM5 PFT level has a lower systematic bias than the CLM5 grid level, indicating a positive effect of the functional disaggregations in CLM5.  Furthermore, we determine Europe's water-use efficiency (WUE) trends from the European CLM5 and remote sensing data and discover significantly decreasing WUE trends in Central and Eastern Europe. The observations confirmed the decreasing WUE in Central Europe, but the underrepresentation of the station network in Eastern Europe hampered the validation of our simulations. Finally, we outline further activities where the eLTER RI and the  European CLM5 can find synergies, including finding recommendations of focus regions for the RI network design, drought analysis, data assimilation, and creating an ecosystem reanalysis streamlining a data service to users of the RI. To conclude, we emphasize the substantial impact on continental, eco-hydrological research that eLTER
already has as an emergent RI, and the high potential for impactful research with the established RI in future.