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NACP Workshop, August 25-27 2010 Boulder CO

A model-data intercomparison of CO 2 exchange across North America: Results from the North American Carbon Program Site Synthesis Christopher R Schwalm 1 , Christopher A. Williams 1 , Kevin Schaefer 2, NACP contributors JGR-Biogeosciences Accepted. NACP Workshop, August 25-27 2010 Boulder CO.

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NACP Workshop, August 25-27 2010 Boulder CO

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  1. A model-data intercomparison of CO2 exchange across North America: Results from the North American Carbon Program Site SynthesisChristopher R Schwalm1, Christopher A. Williams1, Kevin Schaefer2, NACP contributorsJGR-Biogeosciences Accepted NACP Workshop, August 25-27 2010 Boulder CO

  2. Contributors Christopher R. Schwalm, Christopher A. Williams, Kevin Schaefer, Ryan Anderson, M. Altaf Arain, Ian Baker, Alan Barr, T. Andrew Black, Guangsheng Chen, Jing Ming Chen, Philippe Ciais, Kenneth J. Davis, Ankur Desai, Michael Dietze, Danilo Dragoni, Marc L. Fischer, Lawrence B. Flanagan, Robert Grant, Lianhong Gu, David Hollinger, R. César Izaurralde, Chris Kucharik, Peter Lafleur, Beverly E. Law, Longhui Li, Zhengpeng Li, Shuguang Liu, Erandathie Lokupitiya, Yiqi Luo, Siyan Ma, Hank Margolis, Roser Matamala, Harry McCaughey, Russell K. Monson, Walter C. Oechel, Changhui Peng, Benjamin Poulter, David T. Price, Dan M. Riciutto, William Riley, Alok Kumar Sahoo, Michael Sprintsin, Jianfeng Sun, Hanqin Tian, Christina Tonitto, Hans Verbeeck, Shashi B. Verma

  3. Motivation • Are the various measurement and modeling estimates of carbon, water, and energy fluxes at individual sites consistent with each other - and if not, why? • Focus on factors contributing to model-data mismatch • Need to quantify forward ecosystem model skill and sources of uncertainty

  4. Model skill • Monthly NEP • Non-gap-filled data only • Model skill metrics • NMAE (normalized mean absolute error) • S (Taylor skill; 1-number summary of Taylor diagram) • Χ2 (distance between observation and simulation in multiple of observational error) • Biome, climatic season, drought, model structure, site history

  5. Model skill (NMAE) by model, climactic season, and drought level

  6. Models Crop only (n≤ 5) Generalist (n≥ 30 sites) Range RMSE: 0.4 to 1.2 σ: 0.4 to 1.4 ρ: -0.1 to +0.9 Other

  7. 3D surface of model skill

  8. Distribution of model skill (S) Variable importance by site (green) and model structural (blue) attribute

  9. Within-group difference in Taylor skill Small effect sizes despite high variable importance (and statistical significance)

  10. What did we learn? • Overall model performance was poor; the difference between observations and simulations was ~10-times observational uncertainty • Forested ecosystems better simulated than non-forested. • Model-data agreement was highest in summer and in temperate evergreen forests. • Model skill declined in spring and fall, especially in ecosystems with large deciduous components, and in dry periods during the growing season. • Models with the highest skill used prescribed canopy phenology, calculated NEE as the difference between GPP and TER, and did not use a daily time step. • Mean model ensemble, optimized model did well. • One model can be used in all biomes if requisite structure present.

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