Biophysics and vegetation cover change: a process-based evaluation framework for confronting land surface models with satellite observations

Abstract

15Land use and land cover change (LULCC) alter the biophysical properties of the Earth's surface. The associated changes in vegetation cover can perturb the local surface energy balance, which in turn can affect the local climate. The sign and magnitude of this change in climate depends on the specific vegetation transition, its timing and location, as well as on the background climate. Land surface models (LSMs) can be used to simulate such land-climate interactions and study their impact in past and future climates, but their capacity to model biophysical effects accurately across the globe remain unclear 20 due to the complexity of the phenomena. Here we present a framework to evaluate the performance of such models with respect to a dedicated dataset derived from satellite remote sensing observations. Idealized simulations from four LSMs (JULES, ORCHIDEE, JSBACH and CLM) are combined with satellite observations to analyse the changes in radiative and turbulent fluxes caused by 15 specific vegetation cover transitions across geographic, seasonal and climatic gradients. The seasonal variation in net radiation associated with land cover change is the process that models capture best, whereas LSMs 25 perform poorly when simulating spatial and climatic gradients of variation in latent, sensible and ground heat fluxes induced by land cover transitions. We expect that this analysis will help identify model limitations and prioritize efforts in model development as well as to inform where consensus between model and observations is already met, ultimately helping to improve the robustness and consistency of model simulations to better inform land-based mitigation and adaptation policies.

Land Cover Impacts on Land‐Atmosphere Coupling Strength in Climate Simulations With WRF Over Europe

“…On the other hand, it strengthened the predominance of the wet soil advantage on nAC days (Figure S1c). The LULCC responses in surface flux partitioning mostly coincided with the findings of Duveiller, Forzieri, et al (2018) who examined the effects of a suite of vegetation transitions on the radiation and energy balances at the land surface.…”

“…de Noblet‐Ducoudré et al (2012) find that the regional biogeophysical impacts of LULCC can exceed the magnitude of radiative forcing caused by greenhouse gas emissions, although their assessment is still uncertain in sign and magnitude within climate models (Davin & de Noblet‐Ducoudré, 2010). This is because counteracting effects of radiative and nonradiative processes on water and energy exchanges vary in time and space and depend on the type of LULCC (Duveiller, Forzieri, et al, 2018; Duveiller, Hooker, & Cescatti, 2018; Snyder et al, 2004). Deforestation, for example, increases the surface albedo, because cropland or grassland usually have a brighter surface than forests.…”

Evaporative Resistance is of Equal Importance as Surface Albedo in High‐Latitude Surface Temperatures Due to Cloud Feedbacks

“…It is important to note that there is substantial disagreement between different land models for the robustness of biophysical climate responses to vegetation change (De Noblet‐Ducoudré et al, ). While land surface models generally agree with each other, as well as with observations, on the effects of vegetation change on radiative fluxes, there is a much larger disagreement on how vegetation change should impact the partitioning of turbulent energy into sensible and latent heat fluxes (Duveiller et al, ; De Noblet‐Ducoudré et al, ). In addition, atmospheric responses to vegetation change are substantial (Laguë et al, ), which means that models have a large uncertainty in the impact of vegetation change on near‐surface climate not only from differences in the land models and their flux representations but also in the sensitivity of various atmospheric models to changes in land surface fluxes.…”

Evaluating the Interplay Between Biophysical Processes and Leaf Area Changes in Land Surface Models

“…The implicit assumptions with these simulations are that (1) the energy and water fluxes of a given PFT in a pure cell are comparable with those of the same PFT in a mixed cell and (2) potential feedbacks due to the land‐atmosphere interactions were excluded since all simulations were forced with observed climate. More details on the model setup protocol are described in Duveiller et al ().…”