Evapotranspiration uncertainty at micrometeorological scales: The impact of the eddy covariance energy imbalance and correction methods

Authors: BAMBACH, NICOLAS - University Of California, Davis; Kustas, William - Bill; Alfieri, Joseph; Prueger, John; HIPPS, LAWRENCE - Utah State University; McKee, Lynn; CASTRO-BUSTAMANTE, SEBASTIAN - University Of California, Davis; VOLK, J - Desert Research Institute; ALSINA, MARIA - E & J Gallo Winery; McElrone, Andrew

Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2022
Publication Date: 3/26/2022
Citation: Bambach, N.E., Kustas, W.P., Alfieri, J.G., Prueger, J.H., Hipps, L., McKee, L.G., Castro-Bustamante, S., Volk, J., Alsina, M.M., McElrone, A.J. 2022. Evapotranspiration uncertainty at micrometeorological scales: The impact of the eddy covariance energy imbalance and correction methods. Irrigation Science. https://doi.org/10.1007/s00271-022-00783-1.
DOI: https://doi.org/10.1007/s00271-022-00783-1

Interpretive Summary:

Technical Abstract: Evapotranspiration fluxes derived through the eddy covariance technique, in an ideal case, are considered a direct measurement of crop water use. Eddy covariance flux measurements provide estimates at a temporal frequency that allows examining sub-daily, daily, and seasonal scale processes and relationships between different surface fluxes. The Grape Remote Sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX) project has collected micrometeorological and biophysical data aiming to ground-truth new remote sensing tools to fine-tune irrigation management. In this study, we focus on quantifying the impact of using different established approaches to post-process flux tower data. Daily and seasonal actual evapotranspiration estimates derived from different averaging periods; de-spiking, filtering, and gap-filling methods; and energy balance closure approaches. We found that the magnitude of the uncertainty can be up to 37% of the estimated mean daily actual evapotranspiration computed from all the different methods. At seasonal scales, these differences can lead to considerable biases, which in some cases are within the magnitude of the total annual precipitation for a given region. We highlight the importance of recognizing the limitation of the state of the art of observational techniques to quantify canopy scale evapotranspiration. Thus, further advancing micrometeorological techniques should be a key aspect of further advancing remote sensing techniques that require accurate and precise means of validation.