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  A generic pixel-to-point comparison for simulated large-scale ecosystem properties and ground-based observations: an example from the Amazon region

Rammig, A., Heinke, J., Hofhansl, F., Verbeeck, H., Baker, T. R., Christoffersen, B., Ciais, P., De Deurwaerder, H., Fleischer, K., Galbraith, D., Guimberteau, M., Huth, A., Johnson, M., Krujit, B., Langerwisch, F., Meir, P., Papastefanou, P., Sampaio, G., Thonicke, K., Randow, C. v., Zang, C., Rödig, E. (2018): A generic pixel-to-point comparison for simulated large-scale ecosystem properties and ground-based observations: an example from the Amazon region. - Geoscientific Model Development, 11, 12, 5203-5215.

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Rammig, A.1, Author
Heinke, Jens2, Author              
Hofhansl, F.1, Author
Verbeeck, H.1, Author
Baker, T. R.1, Author
Christoffersen, B.1, Author
Ciais, P.1, Author
De Deurwaerder, H.1, Author
Fleischer, K.1, Author
Galbraith, D.1, Author
Guimberteau, M.1, Author
Huth, A.1, Author
Johnson, M.1, Author
Krujit, B.1, Author
Langerwisch, Fanny2, Author              
Meir, P.1, Author
Papastefanou, P.1, Author
Sampaio, G.1, Author
Thonicke, Kirsten2, Author              
Randow, C. von1, Author
Zang, C.1, AuthorRödig, E.1, Author more..
1External Organizations, ou_persistent22              
2Potsdam Institute for Climate Impact Research, ou_persistent13              


Free keywords: -
 Abstract: Comparing model output and observed data is an important step for assessing model performance and quality of simulation results. However, such comparisons are often hampered by differences in spatial scales between local point observations and large-scale simulations of grid cells or pixels. In this study, we propose a generic approach for a pixel-to-point comparison and provide statistical measures accounting for the uncertainty resulting from landscape variability and measurement errors in ecosystem variables. The basic concept of our approach is to determine the statistical properties of small-scale (within-pixel) variability and observational errors, and to use this information to correct for their effect when large-scale area averages (pixel) are compared to small-scale point estimates. We demonstrate our approach by comparing simulated values of aboveground biomass, woody productivity (woody net primary productivity, NPP) and residence time of woody biomass from four dynamic global vegetation models (DGVMs) with measured inventory data from permanent plots in the Amazon rainforest, a region with the typical problem of low data availability, potential scale mismatch and thus high model uncertainty. We find that the DGVMs under- and overestimate aboveground biomass by 25 % and up to 60 %, respectively. Our comparison metrics provide a quantitative measure for model–data agreement and show moderate to good agreement with the region-wide spatial biomass pattern detected by plot observations. However, all four DGVMs overestimate woody productivity and underestimate residence time of woody biomass even when accounting for the large uncertainty range of the observational data. This is because DGVMs do not represent the relation between productivity and residence time of woody biomass correctly. Thus, the DGVMs may simulate the correct large-scale patterns of biomass but for the wrong reasons. We conclude that more information about the underlying processes driving biomass distribution are necessary to improve DGVMs. Our approach provides robust statistical measures for any pixel-to-point comparison, which is applicable for evaluation of models and remote-sensing products.


 Dates: 2018
 Publication Status: Finally published
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.5194/gmd-11-5203-2018
PIKDOMAIN: Climate Impacts & Vulnerabilities - Research Domain II
PIKDOMAIN: Earth System Analysis - Research Domain I
eDoc: 8281
Research topic keyword: Ecosystems
Model / method: Model Intercomparison
Regional keyword: South America
Organisational keyword: RD2 - Climate Resilience
Organisational keyword: RD1 - Earth System Analysis
Working Group: Ecosystems in Transition
Working Group: Land Use and Resilience
 Degree: -



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Title: Geoscientific Model Development
Source Genre: Journal, SCI, Scopus, p3, oa
Publ. Info: -
Pages: - Volume / Issue: 11 (12) Sequence Number: - Start / End Page: 5203 - 5215 Identifier: CoNE: https://publications.pik-potsdam.de/cone/journals/resource/journals185
Publisher: Copernicus