The effect of relative humidity on eddy covariance latent heat flux measurements and its implication for partitioning into transpiration and evaporation

Research output: Contribution to journalResearch articleContributedpeer-review

Contributors

  • Weijie Zhang - , Max Planck Institute for Biogeochemistry, Ghent University (Author)
  • Martin Jung - , Max Planck Institute for Biogeochemistry (Author)
  • Mirco Migliavacca - , Max Planck Institute for Biogeochemistry, European Commission Joint Research Centre Institute (Author)
  • Rafael Poyatos - , CREAF - Centre for Ecological Research and Forestry Applications, Autonomous University of Barcelona (Author)
  • Diego G. Miralles - , Ghent University (Author)
  • Tarek S. El-Madany - , Max Planck Institute for Biogeochemistry (Author)
  • Marta Galvagno - , Environmental Protection Agency of Aosta Valley (Author)
  • Arnaud Carrara - , Mediterranean Center for Environmental Studies (CEAM) (Author)
  • Nicola Arriga - , European Commission Joint Research Centre Institute (Author)
  • Andreas Ibrom - , Technical University of Denmark (Author)
  • Ivan Mammarella - , University of Helsinki (Author)
  • Dario Papale - , Tuscia University, Euro-Mediterranean Center on Climate Change (Author)
  • Jamie R. Cleverly - , James Cook University Queensland (Author)
  • Michael Liddell - , James Cook University Queensland (Author)
  • Georg Wohlfahrt - , University of Innsbruck (Author)
  • Christian Markwitz - , University of Göttingen (Author)
  • Matthias Mauder - , Chair of Meteorology (Author)
  • Eugenie Paul-Limoges - , University of Zurich (Author)
  • Marius Schmidt - , Jülich Research Centre (Author)
  • Sebastian Wolf - , ETH Zurich (Author)
  • Christian Brümmer - , Johann Heinrich von Thunen Institute (Author)
  • M. Altaf Arain - , McMaster University (Author)
  • Silvano Fares - , National Research Council of Italy (CNR) (Author)
  • Tomomichi Kato - , Hokkaido University (Author)
  • Jonas Ardö - , Lund University (Author)
  • Walter Oechel - , San Diego State University, University of Exeter (Author)
  • Chad Hanson - , Oregon State University (Author)
  • Mika Korkiakoski - , University of Helsinki (Author)
  • Sébastien Biraud - , Lawrence Berkeley National Laboratory (Author)
  • Rainer Steinbrecher - , Karlsruhe Institute of Technology (Author)
  • Dave Billesbach - , University of Nebraska-Lincoln (Author)
  • Leonardo Montagnani - , Free University of Bozen-Bolzano (Author)
  • William Woodgate - , University of Queensland, Commonwealth Scientific & Industrial Research Organisation (CSIRO) (Author)
  • Changliang Shao - , Chinese Academy of Agricultural Sciences (Author)
  • Nuno Carvalhais - , Max Planck Institute for Biogeochemistry, NOVA University Lisbon (Author)
  • Markus Reichstein - , Max Planck Institute for Biogeochemistry, Michael Stifel Center Jena for Data-driven and Simulation Science (Author)
  • Jacob A. Nelson - , Max Planck Institute for Biogeochemistry (Author)

Abstract

While the eddy covariance (EC) technique is a well-established method for measuring water fluxes (i.e., evaporation or 'evapotranspiration’, ET), the measurement is susceptible to many uncertainties. One such issue is the potential underestimation of ET when relative humidity (RH) is high (>70%), due to low-pass filtering with some EC systems. Yet, this underestimation for different types of EC systems (e.g. open-path or closed-path sensors) has not been characterized for synthesis datasets such as the widely used FLUXNET2015 dataset. Here, we assess the RH-associated underestimation of latent heat fluxes (LE, or ET) from different EC systems for 163 sites in the FLUXNET2015 dataset. We found that the LE underestimation is most apparent during hours when RH is higher than 70%, predominantly observed at sites using closed-path EC systems, but the extent of the LE underestimation is highly site-specific. We then propose a machine learning based method to correct for this underestimation, and compare it to two energy balance closure based LE correction approaches (Bowen ratio correction, BRC, and attributing all errors to LE). Our correction increases LE by 189% for closed-path sites at high RH (>90%), while BRC increases LE by around 30% for all RH conditions. Additionally, we assess the influence of these corrections on ET-based transpiration (T) estimates using two different ET partitioning methods. Results show opposite responses (increasing vs. slightly decreasing T-to-ET ratios, T/ET) between the two methods when comparing T based on corrected and uncorrected LE. Overall, our results demonstrate the existence of a high RH bias in water fluxes in the FLUXNET2015 dataset and suggest that this bias is a pronounced source of uncertainty in ET measurements to be considered when estimating ecosystem T/ET and WUE.

Details

Original languageEnglish
Article number109305
Pages (from-to)1-11
Number of pages11
JournalAgricultural and forest meteorology
Volume2023
Issue number330
Publication statusE-pub ahead of print - 5 Jan 2023
Peer-reviewedYes

External IDs

ORCID /0000-0002-8789-163X/work/163766097

Keywords

Keywords

  • Eddy covariance, Energy balance closure, Evapotranspiration, FLUXNET, Latent energy