AmeriFlux: Progress and emerging challenges

1. AmeriFlux:Progress and emerging challenges Beverly Law, Oregon State University, AmeriFlux Science Team Chair AmeriFlux Science Steering Group Dennis Baldocchi, University of California, Berkeley David Bowling, University of Utah Jing Chen, University of Toronto Kenneth Davis1, The Pennsylvania State University David Hollinger, USDA Forest Service Xuhui Lee, Yale University Hank Margolis, Laval University William Munger, Harvard University Steven Running, University of Montana Hans Peter Schmid, Forschungszentrum Karlsruhe Peter Thornton, National Center for Atmospheric Research Shashi Verma, University of Nebraska 1presenting

2. outline • Overview of AmeriFlux • Status report • Recent research progress • Emerging challenge: improving climate system modeling • What is needed to meet the challenge?

3. 0. Overview of AmeriFlux

4. AmeriFlux Networkhttp://public.ornl.gov/ameriflux • 93 active sites in 3 countries • 32 research teams • Companion Canadian network • Most major ecoregions in N. America covered • Calibration lab runs comparisons across sites • Open-access, central data base enables global use of observations • Operational since 1996

5. Science objectives • Quantify exchange of carbon, water and energy between terrestrial ecosystems and the atmosphere across a range of vegetation types, disturbance histories, and climatic conditions. • Understand processes governing the terrestrial carbon cycle and linkages with the water, energy and nitrogen cycles. • Produce a high-quality data base and synthesize observations across the network.

6. Core measurements • Fluxes of CO2, water vapor, and sensible heat flux via eddy covariance. • Radiative fluxes and micrometeorological conditions. • Biophysical characterization of sites (e.g. vegetation age and type, nutrient status, carbon pool sizes, soil type).

7. Current AmeriFlux Structure:A Cooperative • Membership requirements: • Address common science questions in strategic plan • Collect certain measurements year-round • Share data in standard format via common database • Participate at annual meetings • Participate in calibration and intercalibration activities • Participate in network-wide syntheses of results • No support or funding comes with membership • e.g. for data management and submission requirements, synthesis contributions • Responsibilities of membership are not binding

8. Characteristics of theCooperative Structure • Structure is very inclusive • participation is broad • growth has been rapid (20 sites 10 years ago, now ~100, 350 worldwide) • Funding structure encourages experimentation and innovation • Each funding cycle, each site must propose something “new” or risk a poor review. • Structure is ideal for learning how to build a network. • Structure is not ideal for maintaining a coherent, long-term network.

9. 1. Status of AmeriFlux

10. AmeriFlux Productivity Data Holdings • 548 site-years of half-hourly data from 100 sites • Flux measurements span 1991-2007 Publications • Investigators have produced roughly 100 peer-reviewed publications/year for the past 5 years. • Multi-site syntheses are increasingly common. http://public.ornl.gov/ameriflux/viewstatus_Ameriflux.cfm Following 3 figures courtesy of Tom Boden

11. AmeriFlux in a global context Number of sites contributing data to the La Thuile Fluxnet global synthesis data base • 74 AmeriFlux sites in Fluxnet dataset account for 305 site-years of data • More than 50 proposals for global synthesis papers received from site investigators. Global data not yet open-access (AmeriFlux portion is open). • About 30% of submitted AmeriFlux site-years were rejected due to incomplete or insufficient quality data - network is somewhat heterogeneous.

12. Length of Data Record and Sponsors for Active AmeriFlux Sites 11 new sites began in 2007 Mean operating age – 5.7 yrs 10 sites operating over a decade but some of these have uncertain future funding Number of sites Number of years of operation for a given site • Major sponsors for active sites – DOE (39), None (17), USDA (15), NOAA (7), NSF(7), Universities (5), and NASA (3). • Non-centralized nature of AmeriFlux leads to instability in the network - potentially high turnover rate among sites.

13. Summary of status • An AmeriFlux network of decadal-scale flux measurements is emerging within a global coop of networks of "standardized" flux and biological measurements. • Coherent network observations are central elements of many new synthesis studies. Research and publication is moving from site studies to network studies. • There is increasing use of network data products by the carbon cycle and climate modeling communities. • There is a recent decrease in the number of funded sites and the potential for a high turnover rate among sites. • Some sites are providing insufficient data for synthesis activities. • Network goals are compromised by funding sites individually.

14. 2. Recent research highlights • Process studies • quantify and understand processes that influence ecosystem-atmosphere interactions • Diagnoses of regional carbon budgets • construct large scale flux estimates • Applications of flux network data to improving climate system modeling

15. Quantification of climate-ecosystem interactions: Clouds, aerosols and ecosystems • AmeriFlux data quantifies the impact of clouds and aerosols on carbon sequestration and evapotranspiration at the land surface • Flux observations showed aerosol and cloud effects on light quality and photosynthesis • Importance of diffuse light effects now being incorporated in regional/global land surface models • Similar process-oriented studies, using single or multiple sites, are ongoing and common across AmeriFlux sites. Net CO2 Flux (mol m-2 s-1) sink Law et al. 2002 Niyogi et al. 2004

16. Diagnoses of regional carbon budgets:Regional clusters of flux towers (Law et al. 2004, Turner et al. 2007) (Desai et al., 2007; in press) Several studies have now combined flux tower observations, satellite remote sensing, environmental conditions and terrestrial carbon cycle models to estimate regional fluxes.

17. r = 0.855 ± 0.175 Diagnosis of regional carbon budgets: MODIS-AmeriFlux synthesis Heinsch et al., 2006 Figures courtesy of Steve Running

18. Improvement of a climate system model using flux network data: NCAR CCSM/CLM example Community Land Model (CLM) versions CLM3.0: original code (Oleson et al. 2004) CLMgw: prognostic ground water scheme, more infiltration, sun-shade canopy etc. CLMgw+rsoil: new bare soil evaporation resistance CLM3.5: diagnostic nitrogen control on Vmax, photosynthesis and stomatal conductance AmeriFlux, Canadian and Amazon sites 8 sites and 52 site-years of data CarboEurope sites 7 sites and 45 site-years of data Temperate, tropical, sub-alpine, boreal and mediterranean sites CLM3.0 vs. CLM3.5 yields large differences in regional hydrologic balances. Courtesy Reto Stoeckli, Colorado State University

19. Terrestrial carbon cycle model Optimized terrestrial carbon cycle model Model prior parameter values (and pdfs) Flux observations (subset) Flux observations (independent set) Biometric data. Soil moisture. Leaf area. Environmental conditions at flux tower site Flux tower site vegetation, soil, and disturbance characteristics Bayesian parameter estimation algorithm Assimilation of flux measurements into terrestrial carbon cycle models for model evaluation 1 Modeled fluxes at tower sites Evaluation 2 Optimized model parameters (and pdfs) Site-years analyzed WLEF: 1997-2004 Harvard: 1992-2003 Howland: 1996-2003 UMBS: 1999-2003 M. Monroe: 1999-2003 TRIFFID model (used in Cox et al., 2000) Ricciuto et al., in prep 3 4 Modeled fluxes at tower sites Evaluation

20. seasonal cycle mean annual flux Assimilation of flux measurements into terrestrial carbon cycle models Diurnal, synoptic and seasonal cycles, and mean annual fluxes can be reproduced well. Interannual variability in mean annual fluxes is not simulated well. Results broadly consistent with previous efforts (e.g. Braswell et al., 2005)

21. 3. Emerging challenge: Evaluate and improve climate prediction/projection using climate system models

22. Problem: Uncertainty in the interaction of the terrestrial carbon cycle and climate • C4MIP: comparison of 10 coupled climate/carbon models. • Large uncertainty (225 ppm range in cumulative atmospheric CO2) in terrestrial biosphere contribution to atmospheric CO2 through 2100. Friedlingstein et al., 2006

23. IPCC WG1 AR4 Summary for Policy Makers Page 14: “Models used to date do not include uncertainties in climate-carbon cycle feedback nor do they include the full effects of changes in ice sheet flow, because a basis in published literature is lacking.” Page 17: “Climate carbon cycle coupling is expected to add carbon dioxide to the atmosphere as the climate system warms, but the magnitude of this feedback is uncertain. This increases the uncertainty in the trajectory of carbon dioxide emissions required to achieve a particular stabilisation level of atmospheric carbon dioxide concentration.”

24. 3rd IPCC report

25. AmeriFlux network record: a fundamental climate system observation

26. AmeriFlux network record: a fundamental climate system observation Causal chain: CO2 fluxes CO2 mixing ratio Surface temperature Note: A single flux measurement does not capture a global value

27. Challenge: Improve predictive skill in coupled climate-carbon cycle modeling • AmeriFlux role: Provide a CO2 flux network data product that can be used as the instrumental temperature record has been used.

28. Future: Poorly maintained network Observational constraints 10 Possible carbon cycle forecasts Future: Well maintained network Current Terrestrial uptake of carbon (GtC yr-1) 5 0 present -5 hindcast forecast Time Potential coupled climate-carbon cycle model evaluation

29. The NCAR Community Climate Systems Model (CCSM) Carbon and Land Model intercomparison Project (C-LAMP) Objectives: • To provide feedback to the science community on the performance of terrestrial biogeochemistry models coupled to CLM within CCSM3 • To provide a new observation-based diagnostics package for terrestrial carbon cycling in coupled carbon-climate models • To define, conceptually, how biogeochemistry should be evaluated in climate models Forrest Hoffman, Peter Thornton, Yen-Huei Lee, Nan Rosenbloom, Jim Randerson, Inez Fung and Steve Running

30. C-LAMP Model Simulations

31. C-LAMPevaluation metrics utilize:flux network data, ecological inventories, remote sensing, atmospheric CO2, ecosystem experiments

32. Role of AmeriFlux within the North American Carbon Program Diagnose, attribute, predict.

33. 4. What is needed to meet this challenge?

34. Observational constraints 10 Possible carbon cycle forecasts Future: Well maintained network Current Terrestrial uptake of carbon (GtC yr-1) 5 0 present -5 hindcast forecast Time Vision

35. Needs • Sustain and enhance a core set of long-term, high-quality flux measurement sites. • Continue mechanistic research to improve model structure and identify important climate-ecosystem interactions • Conduct network design studies • How many sites are needed? • What mix of shorter vs. longer term sites is optimal? • How long are the required time series? • What complementary data are needed at each site? • Sustain and enhance an easily-accessed, homogeneous, data base

36. Summary of status • An AmeriFlux network of decadal-scale flux measurements is emerging within a global coop of networks of "standardized" flux and biological measurements. • Coherent network observations are central elements of many new synthesis studies. Research and publication is moving from site studies to network studies. • There is increasing use of network data products by the carbon cycle and climate modeling communities. • There is a recent decrease in the number of funded sites and the potential for a high turnover rate among sites. • Some sites are providing insufficient data for synthesis activities. • Network goals are compromised by funding sites individually.

37. Recommendations The AmeriFlux science steering group recommends sustaining and enhancing a core network of long-term, high-quality flux measurement sites to address the increasing need for syntheses of multi-site, long-term data records. A coherent network of sites has added value that exceeds a collection of individual, short-term studies. A mechanism should be developed to recognize this added value when questions of funding arise. A stable core network will provide a critical contribution to our ability to predict future climate by enabling the development and evaluation of coupled carbon-climate models and earth systems analysis models.

39. Additional materials in case of questions. Delete when posting talk online.

40. Relationship between AmeriFlux and NEON: Complementary, intersecting efforts

41. Role of AmeriFlux within the North American Carbon Program

42. Topics that can be addressed with integration of AmeriFlux data and models • Where and when will forests be vulnerable to fires, and how do changes in forest processes affect climate? • How would biofuel harvesting impact forest functioning and C sequestration? • How will changes in water availability and population impact water availability to crops and forested watersheds that serve urban areas? • What are potential interactions between future climate scenarios, and carbon, water, and nitrogen cycling?

43. Observed interannual variability: Only local processes? Probably not. Gap-filled fluxes from the 6 midwestern flux tower sites. Interannual variability of similar plant functional types appears to be coherent. Similar processes, linked to climate, influencing sites as far as several hundred kilometers apart in a similar way? LC = wetland; WC, MMSF, UMBS = mature hardwood; Syl = mixed old growth; WLEF = mixed

44. Contributions of AmeriFlux Research to DOE Climate Change Science Program Elements • Climate forcing – carbon cycle, atmospheric water vapor • Climate change prediction • Responses of ecosystems to climate change • Climate mitigation