The WACMOS-ET project – Part 1: Tower-scale evaluation of four remote-sensing-based evapotranspiration algorithms

D. Michel, C. Jiménez, Diego G. Miralles, M. Jung, M. Hirschi, Ali Ershadi, B. Martens, Matthew McCabe, J. B. Fisher, Q. Mu, S. I. Seneviratne, E. F. Wood, D. Fernández-Prieto

Research output: Contribution to journalArticlepeer-review

166 Scopus citations

Abstract

The WAter Cycle Multi-mission Observation Strategy EvapoTranspiration (WACMOS-ET) project has compiled a forcing data set covering the period 2005 2007 that aims to maximize the exploitation of European Earth Observations data sets for evapotranspiration (ET) estimation. The data set was used to run four  established ET algorithms: the Priestley Taylor Jet Propulsion Laboratory model (PT-JPL), the Penman Monteith algorithm from the MODerate resolution Imaging Spectroradiometer (MODIS) evaporation product  (PM-MOD), the Surface Energy Balance System  (SEBS) and the Global Land Evaporation Amsterdam Model  (GLEAM). In addition, in situ meteorological data from 24  FLUXNET towers were used to force the models, with results from both forcing sets compared to tower-based flux observations. Model performance was assessed on several timescales using both sub-daily and daily forcings. The PT-JPL model and GLEAM provide the best performance for both satellite- and tower-based forcing as well as for the considered temporal resolutions. Simulations using the PM-MOD were mostly underestimated, while the SEBS performance was characterized by a systematic overestimation. In general, all four algorithms produce the best results in wet and moderately wet climate regimes. In dry regimes, the correlation and the absolute agreement with the reference tower ET observations were consistently lower. While ET derived with in situ forcing data agrees best with the tower measurements ($\textit{R}$^{2} €¯ = €¯0.67), the agreement of the satellite-based ET estimates is only marginally lower ($\textit{R}$^{2} €¯ = €¯0.58). Results also show similar model performance at daily and sub-daily (3-hourly) resolutions. Overall, our validation experiments against in situ measurements indicate that there is no single best-performing algorithm across all biome and forcing types. An extension of the evaluation to a larger selection of 85  towers (model inputs resampled to a common grid to facilitate global estimates) confirmed the original findings.
Original languageEnglish (US)
Pages (from-to)803-822
Number of pages20
JournalHydrology and Earth System Sciences
Volume20
Issue number2
DOIs
StatePublished - Feb 23 2016

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This study was funded by the European Space
Agency (ESA) and conducted as part of the project WACMOS-ET
(Contract no. 4000106711/12/I-NB). D. G. Miralles acknowledges
the financial support from the Netherlands Organization for Scientific Research through grant 863.14.004 and the Belgian Science
Policy Office (BELSPO) in the framework of the STEREO III
programme, project SAT-EX (SR/00/306). M. F. McCabe and
A. Ershadi acknowledge the support of the King Abdullah University of Science and Technology. The SEBS team is acknowledged
for facilitating discussions concerning the implementation of
their model. This work used eddy-covariance data acquired by
the FLUXNET community and in particular by the following
networks: AmeriFlux (US Department of Energy, Biological and
Environmental Research, Terrestrial Carbon Program, DE-FG02-
04ER63917 and DE-FG02-04ER63911), AfriFlux, AsiaFlux,
CarboAfrica, CarboEuropeIP, CarboItaly, CarboMont, ChinaFlux,
Fluxnet-Canada (supported by CFCAS, NSERC, BIOCAP, Envi-
ronment Canada and NRCan), GreenGrass, KoFlux, LBA, NECC,
OzFlux, TCOS-Siberia and USCCC. Data and logistical support
for the station US-Wrc were provided by the US Forest Service
Pacific Northwest Research Station. All WACMOS-ET forcing
data and ET estimates are publicly available and can be requested
through the project website (http://wacmoset.estellus.eu).

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