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A model-data intercomparison of CO2 exchange across North America: results from the North American Carbon Program site synthesis

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Abstract
Our current understanding of terrestrial carbon processes is represented in various models used to integrate and scale measurements of CO2 exchange from remote sensing and other spatiotemporal data. Yet assessments are rarely conducted to determine how well models simulate carbon processes across vegetation types and environmental conditions. Using standardized data from the North American Carbon Program we compare observed and simulated monthly CO2 exchange from 44 eddy covariance flux towers in North America and 22 terrestrial biosphere models. The analysis period spans similar to 220 site-years, 10 biomes, and includes two large-scale drought events, providing a natural experiment to evaluate model skill as a function of drought and seasonality. We evaluate models' ability to simulate the seasonal cycle of CO2 exchange using multiple model skill metrics and analyze links between model characteristics, site history, and model skill. Overall model performance was poor; the difference between observations and simulations was similar to 10 times observational uncertainty, with forested ecosystems better predicted than nonforested. Model-data agreement was highest in summer and in temperate evergreen forests. In contrast, model performance declined in spring and fall, especially in ecosystems with large deciduous components, and in dry periods during the growing season. Models used across multiple biomes and sites, the mean model ensemble, and a model using assimilated parameter values showed high consistency with observations. Models with the highest skill across all biomes all used prescribed canopy phenology, calculated NEE as the difference between GPP and ecosystem respiration, and did not use a daily time step.
Keywords
GLOBAL VEGETATION MODEL, NET ECOSYSTEM EXCHANGE, MIXED HARDWOOD FOREST, EDDY COVARIANCE DATA, LEAF-AREA INDEX, INTERANNUAL VARIABILITY, DIOXIDE EXCHANGE, PRIMARY PRODUCTIVITY, UNITED-STATES, ATMOSPHERE EXCHANGE

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Chicago
Schwalm, Christopher R, Christopher A Williams, Kevin Schaefer, Ryan Anderson, M Altaf Arain, Ian Baker, Alan Barr, et al. 2010. “A Model-data Intercomparison of CO2 Exchange Across North America: Results from the North American Carbon Program Site Synthesis.” Journal of Geophysical Research-biogeosciences 115.
APA
Schwalm, C. R., Williams, C. A., Schaefer, K., Anderson, R., Arain, M. A., Baker, I., Barr, A., et al. (2010). A model-data intercomparison of CO2 exchange across North America: results from the North American Carbon Program site synthesis. JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES, 115.
Vancouver
1.
Schwalm CR, Williams CA, Schaefer K, Anderson R, Arain MA, Baker I, et al. A model-data intercomparison of CO2 exchange across North America: results from the North American Carbon Program site synthesis. JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES. 2010;115.
MLA
Schwalm, Christopher R, Christopher A Williams, Kevin Schaefer, et al. “A Model-data Intercomparison of CO2 Exchange Across North America: Results from the North American Carbon Program Site Synthesis.” JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES 115 (2010): n. pag. Print.
@article{1091566,
  abstract     = {Our current understanding of terrestrial carbon processes is represented in various models used to integrate and scale measurements of CO2 exchange from remote sensing and other spatiotemporal data. Yet assessments are rarely conducted to determine how well models simulate carbon processes across vegetation types and environmental conditions. Using standardized data from the North American Carbon Program we compare observed and simulated monthly CO2 exchange from 44 eddy covariance flux towers in North America and 22 terrestrial biosphere models. The analysis period spans similar to 220 site-years, 10 biomes, and includes two large-scale drought events, providing a natural experiment to evaluate model skill as a function of drought and seasonality. We evaluate models' ability to simulate the seasonal cycle of CO2 exchange using multiple model skill metrics and analyze links between model characteristics, site history, and model skill. Overall model performance was poor; the difference between observations and simulations was similar to 10 times observational uncertainty, with forested ecosystems better predicted than nonforested. Model-data agreement was highest in summer and in temperate evergreen forests. In contrast, model performance declined in spring and fall, especially in ecosystems with large deciduous components, and in dry periods during the growing season. Models used across multiple biomes and sites, the mean model ensemble, and a model using assimilated parameter values showed high consistency with observations. Models with the highest skill across all biomes all used prescribed canopy phenology, calculated NEE as the difference between GPP and ecosystem respiration, and did not use a daily time step.},
  articleno    = {G00H05},
  author       = {Schwalm, Christopher R and Williams, Christopher A and Schaefer, Kevin and Anderson, Ryan and Arain, M Altaf and Baker, Ian and Barr, Alan and Black, T Andrew and Chen, Guangsheng and Chen, Jing Ming and Ciais, Philippe and Davis, Kenneth J and Desai, Ankur and Dietze, Michael and Dragoni, Danilo and Fischer, Marc L and Flanagan, Lawrence B and Grant, Robert and Gu, Lianhong and Hollinger, David and Izaurralde, R C{\'e}sar and Kucharik, Chris and Lafleur, Peter and Law, Beverly E and Li, Longhui and Li, Zhengpeng and Liu, Shuguang and Lokupitiya, Erandathie and Luo, Yiqi and Ma, Siyan and Margolis, Hank and Matamala, Roser and McCaughey, Harry and Monson, Russell K and Oechel, Walter C and Peng, Changhui and Poulter, Benjamin and Price, David T and Riciutto, Dan M and Riley, William and Sahoo, Alok Kumar and Sprintsin, Michael and Sun, Jianfeng and Tian, Hanqin and Tonitto, Christina and Verbeeck, Hans and Verma, Shashi B},
  issn         = {0148-0227},
  journal      = {JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES},
  keyword      = {GLOBAL VEGETATION MODEL,NET ECOSYSTEM EXCHANGE,MIXED HARDWOOD FOREST,EDDY COVARIANCE DATA,LEAF-AREA INDEX,INTERANNUAL VARIABILITY,DIOXIDE EXCHANGE,PRIMARY PRODUCTIVITY,UNITED-STATES,ATMOSPHERE EXCHANGE},
  language     = {eng},
  pages        = {22},
  title        = {A model-data intercomparison of CO2 exchange across North America: results from the North American Carbon Program site synthesis},
  url          = {http://dx.doi.org/10.1029/2009JG001229},
  volume       = {115},
  year         = {2010},
}

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