The GEWEX LandFlux project : evaluation of model evaporation using tower-based and globally gridded forcing dataReportar como inadecuado

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(2016)GEOSCIENTIFIC MODEL DEVELOPMENT.9(1).p.283-305 Mark abstract Determining the spatial distribution and temporal development of evaporation at regional and global scales is required to improve our understanding of the coupled wa- ter and energy cycles and to better monitor any changes in observed trends and variability of linked hydrological processes. With recent international efforts guiding the de- velopment of long-term and globally distributed flux esti- mates, continued product assessments are required to inform upon the selection of suitable model structures and also to establish the appropriateness of these multi-model simula- tions 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 cli- mate zones. The selected schemes include the Surface En- ergy 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 quantify- ing 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 Land-Flux product can be obtained, while also providing a relative evaluation and assessment of model performance.Using surface flux observations from 45 globally dis- tributed 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 R2, RMSD and Nash–Sutcliffe efficiency (NSE), respec- tively. PM-Mu (0.51; 78 W m−2; 0.45) tended to underesti- mate fluxes, while SEBS (0.72; 101 W m−2 ; 0.24) overes- timated values relative to observations. A focused analysis across specific biome types and climate zones showed con- siderable 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 mis- match and issues related to forcing quality. Rather than rely- ing on any single model simulation, the spatial and tempo- ral 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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Autor: MF McCabe, A Ershadi, C Jimenez, Diego Gonzalez Miralles , D Michel and EF Wood



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