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Jonas Ardö

Professor

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

Författare

  • Weijie Zhang
  • Martin Jung
  • Mirco Migliavacca
  • Rafael Poyatos
  • Diego G. Miralles
  • Tarek S. El-Madany
  • Marta Galvagno
  • Arnaud Carrara
  • Nicola Arriga
  • Andreas Ibrom
  • Ivan Mammarella
  • Dario Papale
  • Jamie R. Cleverly
  • Michael Liddell
  • Georg Wohlfahrt
  • Christian Markwitz
  • Matthias Mauder
  • Eugenie Paul-Limoges
  • Marius Schmidt
  • Sebastian Wolf
  • Christian Brümmer
  • M. Altaf Arain
  • Silvano Fares
  • Tomomichi Kato
  • Jonas Ardö
  • Walter Oechel
  • Chad Hanson
  • Mika Korkiakoski
  • Sébastien Biraud
  • Rainer Steinbrecher
  • Dave Billesbach
  • Leonardo Montagnani
  • William Woodgate
  • Changliang Shao
  • Nuno Carvalhais
  • Markus Reichstein
  • Jacob A. Nelson
Visa allt

Summary, in English

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.

Avdelning/ar

  • Institutionen för naturgeografi och ekosystemvetenskap
  • BECC: Biodiversity and Ecosystem services in a Changing Climate

Publiceringsår

2023-03-01

Språk

Engelska

Publikation/Tidskrift/Serie

Agricultural and Forest Meteorology

Volym

330

Dokumenttyp

Artikel i tidskrift

Förlag

Elsevier

Ämne

  • Oceanography, Hydrology, Water Resources

Nyckelord

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

Status

Published

ISBN/ISSN/Övrigt

  • ISSN: 0168-1923