TY - JOUR
T1 - The GEWEX LandFlux project
T2 - Evaluation of model evaporation using tower-based and globally gridded forcing data
AU - McCabe, M. F.
AU - Ershadi, A.
AU - Jimenez, C.
AU - Miralles, D. G.
AU - Michel, D.
AU - Wood, Eric F.
N1 - Funding Information:
Research reported in this publication was supported by the King Abdullah University of Science and Technology (KAUST). D. G. Miralles acknowledges the financial support from The Netherlands Organization for Scientific Research through grant 863.14.004. We appreciate the support of the ESA funded WACMOS-ET project for both fruitful scientific discussions and guidance in ensuring complementarity of these joint efforts. We thank the FLUXNET site investigators for allowing for the use of their meteorological data. This work used eddy-covariance data acquired by the FLUXNET community and in particular by the AmeriFlux program (U.S. 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, Environment Canada, and NRCan), GreenGrass, KoFlux, LBA, NECC, TCOS-Siberia, USCCC. We acknowledge the financial support to the eddy-covariance data harmonisation provided by CarboEuropeIP, FAO-GTOS-TCO, iLEAPS, Max Planck Institute for Biogeochemistry, National Science Foundation, University of Tuscia, Université Laval and Environment Canada and US Department of Energy and the database development and technical support from Berkeley Water Centre, Lawrence Berkeley National Laboratory, Microsoft Research eScience, Oak Ridge National Laboratory, University of California – Berkeley, University of Virginia.
Publisher Copyright:
© Author(s) 2016.
PY - 2016/1/26
Y1 - 2016/1/26
N2 - 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 to 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; 61Wm-2; 0.65), followed closely by GLEAM (0.68; 64Wm-2; 0.62), with values in parentheses representing the R2, RMSD and Nash-Sutcliffe efficiency (NSE), respectively. PM-Mu (0.51; 78Wm-2; 0.45) tended to underestimate fluxes, while SEBS (0.72; 101 Wm-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. Challenges related to the robust assessment of the LandFlux product are also discussed.
AB - 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 to 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; 61Wm-2; 0.65), followed closely by GLEAM (0.68; 64Wm-2; 0.62), with values in parentheses representing the R2, RMSD and Nash-Sutcliffe efficiency (NSE), respectively. PM-Mu (0.51; 78Wm-2; 0.45) tended to underestimate fluxes, while SEBS (0.72; 101 Wm-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. Challenges related to the robust assessment of the LandFlux product are also discussed.
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U2 - 10.5194/gmd-9-283-2016
DO - 10.5194/gmd-9-283-2016
M3 - Article
AN - SCOPUS:84956694930
VL - 9
SP - 283
EP - 305
JO - Geoscientific Model Development
JF - Geoscientific Model Development
SN - 1991-959X
IS - 1
ER -