Title: The GEWEX LandFlux project: Evaluation of model evaporation using tower-based and globally gridded forcing data

Abstract

Determining the spatial distribution and temporal development of evaporation at regional and global scales is required to improve our understanding of the coupled water and energy cycles and to better monitor any changes in observed trends and variability of linked hydrological processes. With recent international efforts guiding the development of long-term and globally distributed flux estimates, continued product assessments are required to inform upon the selection of suitable model structures and also to establish the appropriateness of these multi-model simulations for global application. In support of the objectives of the Global Energy and Water Cycle Exchanges (GEWEX) LandFlux project, four commonly used evaporation models are evaluated against data from tower-based eddy-covariance observations, distributed across a range of biomes and climate zones. The selected schemes include the Surface Energy Balance System (SEBS) approach, the Priestley–Taylor Jet Propulsion Laboratory (PT-JPL) model, the Penman–Monteith-based Mu model (PM-Mu) and the Global Land Evaporation Amsterdam Model (GLEAM). Here we seek to examine the fidelity of global evaporation simulations by examining the multi-model response to varying sources of forcing data. To do this, we perform parallel and collocated model simulations using tower-based data together with a global-scale grid-based forcing product. Through quantifying the multi-model response tomore » high-quality tower data, a better understanding of the subsequent model response to the coarse-scale globally gridded data that underlies the LandFlux product can be obtained, while also providing a relative evaluation and assessment of model performance. Using surface flux observations from 45 globally distributed eddy-covariance stations as independent metrics of performance, the tower-based analysis indicated that PT-JPL provided the highest overall statistical performance (0.72; 61 W m ^–2; 0.65), followed closely by GLEAM (0.68; 64 W m ^–2; 0.62), with values in parentheses representing the R ², RMSD and Nash–Sutcliffe efficiency (NSE), respectively. PM-Mu (0.51; 78 W m ^–2; 0.45) tended to underestimate fluxes, while SEBS (0.72; 101 W m ^–2; 0.24) overestimated values relative to observations. A focused analysis across specific biome types and climate zones showed considerable variability in the performance of all models, with no single model consistently able to outperform any other. Results also indicated that the global gridded data tended to reduce the performance for all of the studied models when compared to the tower data, likely a response to scale mismatch and issues related to forcing quality. Rather than relying on any single model simulation, the spatial and temporal variability at both the tower- and grid-scale highlighted the potential benefits of developing an ensemble or blended evaporation product for global-scale LandFlux applications. Hence, challenges related to the robust assessment of the LandFlux product are also discussed.« less

Authors:

McCabe, M. F.  ^[1];

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Ershadi, A. ^[1]; Jimenez, C. ^[2]; Miralles, D. G.  ^[3];

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Michel, D. ^[4]; Wood, E. F. ^[5]

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+ Show Author Affiliations

1. King Abdullah Univ. of Science and Technology, Thuwal, (Saudi Arabia). Div. of Biological and Environmental Sciences and Engineering
2. Estellus, Paris (France)
3. Univ. Amsterdam, Amsterdam, (Netherlands). Dept. of Earth Sciences VU
4. Inst. for Atmospheric and Climate Sciences, ETH Zurich, Zurich, (Switzerland)
5. Princeton Univ., Princeton, NJ, (United States). Dept. of Civil and Environmental Engineering

Publication Date:

2016-01-26

Research Org.:

Princeton Univ., NJ (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); King Abdullah University of Science and Technology (KAUST); Netherlands Organization for Scientific Research (NWO); ESA; CFCAS; Natural Sciences and Engineering Research Council of Canada (NSERC); BIOCAP; Environment Canada; NRCan; CarboEuropeIP; FAO-GTOS-TCO; iLEAPS; Max Planck Institute for Biogeochemistry; National Science Foundation (NSF); University of Tuscia; Universite Laval

OSTI Identifier:

1268175

Grant/Contract Number:  

FG02-04ER63917; FG02-04ER63911

Resource Type:

Accepted Manuscript

Journal Name:

Geoscientific Model Development (Online)

Additional Journal Information:

Journal Name: Geoscientific Model Development (Online); Journal Volume: 9; Journal Issue: 1; Journal ID: ISSN 1991-9603

Publisher:

European Geosciences Union

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; gross primary productivity; light-use efficiency; balance system sebs; eddy-covariance; energy-balance; surface-temperature; carbon-dioxide; heat-flux; evapotranspiration algorithm; ecosystem productivity