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Volume 20, issue 2 | Copyright
Hydrol. Earth Syst. Sci., 20, 823-842, 2016
https://doi.org/10.5194/hess-20-823-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 23 Feb 2016

Research article | 23 Feb 2016

The WACMOS-ET project – Part 2: Evaluation of global terrestrial evaporation data sets

D. G. Miralles1,2, C. Jiménez3, M. Jung4, D. Michel5, A. Ershadi6, M. F. McCabe6, M. Hirschi5, B. Martens2, A. J. Dolman1, J. B. Fisher7, Q. Mu8, S. I. Seneviratne5, E. F. Wood9, and D. Fernández-Prieto10 D. G. Miralles et al.
  • 1Department of Earth Sciences, VU University Amsterdam, Amsterdam, the Netherlands
  • 2Laboratory of Hydrology and Water Management, Ghent University, Ghent, Belgium
  • 3Estellus, Paris, France
  • 4Max Planck Institute for Biogeochemistry, Jena, Germany
  • 5Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
  • 6Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
  • 7Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
  • 8Department of Ecosystem and Conservation Sciences, University of Montana, Missoula, Montana, USA
  • 9Department of Civil and Environmental Engineering, Princeton University, Princeton, New Jersey, USA
  • 10ESRIN, European Space Agency, Frascati, Italy

Abstract. The WAter Cycle Multi-mission Observation Strategy – EvapoTranspiration (WACMOS-ET) project aims to advance the development of land evaporation estimates on global and regional scales. Its main objective is the derivation, validation, and intercomparison of a group of existing evaporation retrieval algorithms driven by a common forcing data set. Three commonly used process-based evaporation methodologies are evaluated: the Penman–Monteith algorithm behind the official Moderate Resolution Imaging Spectroradiometer (MODIS) evaporation product (PM-MOD), the Global Land Evaporation Amsterdam Model (GLEAM), and the Priestley–Taylor Jet Propulsion Laboratory model (PT-JPL). The resulting global spatiotemporal variability of evaporation, the closure of regional water budgets, and the discrete estimation of land evaporation components or sources (i.e. transpiration, interception loss, and direct soil evaporation) are investigated using river discharge data, independent global evaporation data sets and results from previous studies. In a companion article (Part 1), Michel et al. (2016) inspect the performance of these three models at local scales using measurements from eddy-covariance towers and include in the assessment the Surface Energy Balance System (SEBS) model. In agreement with Part 1, our results indicate that the Priestley and Taylor products (PT-JPL and GLEAM) perform best overall for most ecosystems and climate regimes. While all three evaporation products adequately represent the expected average geographical patterns and seasonality, there is a tendency in PM-MOD to underestimate the flux in the tropics and subtropics. Overall, results from GLEAM and PT-JPL appear more realistic when compared to surface water balances from 837 globally distributed catchments and to separate evaporation estimates from ERA-Interim and the model tree ensemble (MTE). Nonetheless, all products show large dissimilarities during conditions of water stress and drought and deficiencies in the way evaporation is partitioned into its different components. This observed inter-product variability, even when common forcing is used, suggests that caution is necessary in applying a single data set for large-scale studies in isolation. A general finding that different models perform better under different conditions highlights the potential for considering biome- or climate-specific composites of models. Nevertheless, the generation of a multi-product ensemble, with weighting based on validation analyses and uncertainty assessments, is proposed as the best way forward in our long-term goal to develop a robust observational benchmark data set of continental evaporation.

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The WACMOS-ET project aims to advance the development of land evaporation estimates on global and regional scales. Evaluation of current evaporation data sets on the global scale showed that they manifest large dissimilarities during conditions of water stress and drought and deficiencies in the way evaporation is partitioned into several components. Different models perform better under different conditions, highlighting the potential for considering biome- or climate-specific model ensembles.
The WACMOS-ET project aims to advance the development of land evaporation estimates on global...
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