The role of land-surface interactions for the surface energy fluxes in the EC-Earth earth system model

The EC-Earth earth system model is characterized by biases in various aspects of the simulated climate. Biases in precipitation result in biases in soil moisture, while biases in temperature and precipitation contribute to biases in vegetation. In this study, the extent to which the biases in soil moisture and vegetation contribute to the biases in the surface energy fluxes (which, in turn, lead to near-surface climate biases) in EC-Earth through interactions with the atmosphere is investigated.

The study is based on two simulations for the recent period 19719-2017: an offline simulation with the land-surface component of EC-Earth, combining the HTESSEL land surface model and the LPJ-GUESS dynamical vegetation model forced, by the meteorological conditions from the ERA5 re-analyses, and a simulation with the atmospheric version of EC-Earth, where the land-surface conditions, i.e., soil moisture and vegetation, are prescribed from the offline simulation.

The purpose of the study is twofold: By comparing the offline simulation with the land-surface component of EC-Earth with observational estimates of the surface energy fluxes, it is investigated to which extent the land-surface component, combing HTESSEL and LPJ-GUESS, is capable to simulate the surface energy fluxes under “perfect” climate conditions. And by comparing the simulation with the atmospheric component of EC-Earth with the offline simulation, the effects of the land-surface atmosphere interactions on the biases of the surface energy fluxes in EC-Earth are assessed. These effects are, to a large extent, related to climate biases in the atmospheric component of EC-Earth, e.g., the radiative fluxes, precipitation or the near-surface climate conditions.