Preprints
https://doi.org/10.5194/gmd-2022-216
https://doi.org/10.5194/gmd-2022-216
Submitted as: model evaluation paper
08 Nov 2022
Submitted as: model evaluation paper | 08 Nov 2022
Status: this preprint is currently under review for the journal GMD.

Getting the leaves right matters for estimating temperature extremes

Gregory Duveiller1,2, Mark Pickering3, Joaquin Muñoz-Sabater4, Luca Caporaso2, Souhail Boussetta4, Gianpaolo Balsamo4, and Alessandro Cescatti2 Gregory Duveiller et al.
  • 1Max Planck Institute for Biogeochemistry, Jena, Germany
  • 2European Commission Joint Research Centre, Ispra, Italy
  • 3JRC consultant, Ispra, Italy
  • 4European Centre for Medium Range Weather Forecasts, Reading, UK

Abstract. Atmospheric reanalyses combine observations and models through data assimilation techniques to provide spatio-temporally continuous fields of key surface variables. They can do so for extended historical periods whilst ensuring a coherent representation of the main Earth system cycles. ERA5, and its enhanced land surface component ERA5-Land, are widely used in Earth System science and form the flagship products of the Copernicus Climate Change Service (C3S) of the European Commission. Such land surface modelling frameworks generally rely on a state variable called leaf area index (LAI), representing the amount of leaves in a grid cell at a given time, to quantify the fluxes of carbon, water and energy between the vegetation and the atmosphere. However, the LAI within the modelling framework behind ERA5 and ERA5-Land is prescribed as a climatological seasonal cycle, neglecting any inter-annual variability and the potential consequences that this uncoupling between vegetation and atmosphere may have on the surface energy balance and the climate. To evaluate the impact of this mismatch in LAI, we analyse the corresponding effect it has on land surface temperature (LST) by comparing what is simulated to satellite observations. We characterise a hysteretic behaviour between LST biases and LAI biases that evolves differently along the year depending on the background climate. We further analyse their repercussion on the reconstructed climate during the more extreme conditions in terms of LAI deviations, with a specific focus on the 2003, 2010 and 2018 heatwaves in Europe where LST mismatches are exacerbated. We anticipate that our results will assist users of ERA5 and ERA5-Land data to understand where and when the larger discrepancies can be expected, but also guide developers towards improving the modelling framework. Finally, this study could provide a blueprint for a wider benchmarking framework for land surface model evaluation that exploits the capacity of LST to integrate the effects of both radiative and non-radiative processes affecting the surface energy.

Gregory Duveiller et al.

Status: open (until 06 Jan 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Gregory Duveiller et al.

Data sets

Dataset in support of the study "Getting the leaves right matters for estimating temperature extremes" Mark Pickering & Gregory Duveiller https://doi.org/10.5281/zenodo.6976942

Model code and software

Code in support of the study "Getting the leaves right matters for estimating temperature extremes" Gregory Duveiller & Mark Pickering https://doi.org/10.5281/zenodo.7275088

Gregory Duveiller et al.

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Short summary
Some of our best tools to describe the state of the land system, including the intensity of heatwaves, have a problem. The model behind currently assumes that the amount of leaves in ecosystems always follow the same cycle. By using satellite observations of when the leaves are present, we show that getting the yearly changes in this cycle is important to avoid errors in estimating surface temperature. We show this has strong implications on our capacity to describe heatwaves across Europe.