Uncertainties in land-atmosphere coupling still a big obstacle for accurate climate projections

Terrestrial energy, water and carbon exchanges are regulated by the strength and sign of the coupling between the land surface and the atmosphere. Simulating this land-atmosphere coupling is crucial for realistic weather and climate projections and, especially, to anticipate the evolution of extreme events. After an exploration of the metrics and datasets available for studying land-atmosphere coupling at different temporal and spatial scales, we demonstrate that uncertainties in data products based on in-situ measurements, remote sensing data, and Earth System Model simulations remain large. The evaluation of model simulations according to a variety of land-atmosphere coupling metrics reveals large structural uncertainties in comparison with the small effect of internal variability on land-atmosphere coupling. We show that reducing uncertainties in available Earth Observations (EO) products for studying land-atmosphere coupling is also necessary. This could be done by collecting long-term measurements at the land surface and implementing more observational and physical constraints in the algorithms used to derive EO products. The availability of more accurate, physically consistent EO products with an accurate representation of land-atmosphere coupling will in turn help to develop the future generation of Earth System Models.