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Discussion papers | Copyright
https://doi.org/10.5194/hess-2017-682
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 12 Feb 2018

Research article | 12 Feb 2018

Review status
This discussion paper is a preprint. It has been under review for the journal Hydrology and Earth System Sciences (HESS). The revised manuscript was not accepted.

Potential evaporation at eddy-covariance sites across the globe

Wouter H. Maes1, Pierre Gentine2, Niko E. C. Verhoest1, and Diego G. Miralles1 Wouter H. Maes et al.
  • 1Laboratory of Hydrology and Water Management, Ghent University, Coupure Links 653, 9000 Gent, Belgium
  • 2Department of Earth and Environmental Engineering, Columbia University, New York, 10027, USA

Abstract. Potential evaporation (Ep) is a crucial variable for hydrological forecast and in drought monitoring systems. However, multiple interpretations of Ep exist, and these reflect a diverse range of methods to calculate Ep. As such, a comparison of the performance of these methods against field observations in different global ecosystems is badly needed. In this study, we used eddy-covariance measurements from 107 sites of the FLUXNET2015 database, covering 11 different biomes, to parameterize and compare the main Ep methods and uncover their relative performance. For each site, we extracted the days for which ecosystems are unstressed based on both an energy balance approach and on a soil water content approach. The evaporation measurements during these days were used as reference to validate the different methods to estimate Ep. Our results indicate that a simple radiation-driven method calibrated per biome consistently performed best, with a mean correlation of 0.93, an unbiased RMSE of 0.56mmday−1, and a bias of −0.02mmday−1 against in situ measurements of unstressed evaporation. A Priestley and Taylor method, calibrated per biome, performed just slightly worse, yet substantially and consistently better than more complex Penman, Penman-Monteith-based or temperature-based approaches. We show that the poor performance of Penman-Monteith based approaches relates largely to the fact that the unstressed stomatal conductance was assumed constant. Further analysis showed that the biome-specific parameters required for the simple radiation-driven methods are relatively constant per biome. This makes this simple radiation-driven method calibrated per biome a robust method that can be incorporated into models for improving our understanding of the impact of global warming on future global water use and demand, drought severity and ecosystem productivity.

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Wouter H. Maes et al.
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Status: closed
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AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Wouter H. Maes et al.
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Sample code and sample dataset W. H. Maes, P. Gentine, N. E. C. Verhoest, and D. G. Miralles https://doi.org/10.5281/zenodo.1169909

Wouter H. Maes et al.
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Latest update: 24 Sep 2018
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Short summary
Potential evaporation is a key parameter in numerous models used for assessing water use and drought severity. Yet, multiple incompatible methods have been proposed, thus estimates of potential evaporation remain uncertain. Based on the largest available dataset of FLUXNET data, we identify the best method to calculate potential evaporation globally. A simple radiation-driven method calibrated per biome consistently performed best; more complex models did not perform as good.
Potential evaporation is a key parameter in numerous models used for assessing water use and...
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