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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

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Ameriflux progress and emerging challenges l.jpg

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


Outline l.jpg
outline

  • Overview of AmeriFlux

  • Status report

  • Recent research progress

  • Emerging challenge: improving climate system modeling

  • What is needed to meet the challenge?



Ameriflux network http public ornl gov ameriflux l.jpg
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


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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.


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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).


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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


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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.



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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


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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.


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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.


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  • Summary of status Sites

  • 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.


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  • 2. Recent research highlights Sites

  • 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


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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


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Diagnoses of regional carbon budgets: aerosols and ecosystemsRegional 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.


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r = 0.855 ± 0.175 aerosols and ecosystems

Diagnosis of regional carbon budgets: MODIS-AmeriFlux synthesis

Heinsch et al., 2006

Figures courtesy of Steve Running


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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


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Terrestrial carbon cycle model data: NCAR CCSM/CLM example

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


Assimilation of flux measurements into terrestrial carbon cycle models l.jpg

seasonal cycle data: NCAR CCSM/CLM example

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)


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3. Emerging challenge: data: NCAR CCSM/CLM example

Evaluate and improve climate prediction/projection using climate system models


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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


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IPCC WG1 AR4 Summary for Policy Makers carbon cycle and climate

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.”


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3rd IPCC carbon cycle and climate

report



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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


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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.


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Future: Poorly maintained network climate-carbon cycle modeling

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


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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


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C-LAMP Model Simulations Land Model intercomparison Project (C-LAMP)


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C-LAMP Land Model intercomparison Project (C-LAMP)evaluation metrics utilize:flux network data, ecological inventories, remote sensing, atmospheric CO2, ecosystem experiments


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Role of AmeriFlux within the North American Carbon Program Land Model intercomparison Project (C-LAMP)

Diagnose, attribute, predict.


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4. What is needed to meet this challenge? Land Model intercomparison Project (C-LAMP)


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Observational constraints Land Model intercomparison Project (C-LAMP)

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


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Needs Land Model intercomparison Project (C-LAMP)

  • 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


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  • Summary of status Land Model intercomparison Project (C-LAMP)

  • 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.


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Recommendations Land Model intercomparison Project (C-LAMP)

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.


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Additional materials in case of questions. Land Model intercomparison Project (C-LAMP)

Delete when posting talk online.




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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?


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Observed interannual variability: data and modelsOnly 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


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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