Multi-tower Synthesis Scaling of Regional Carbon Dioxide Flux

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Multi-tower Synthesis Scaling of Regional Carbon
Dioxide Flux

• Another fine mess of observed data, remote
  sensing and ecosystem model parameterization

Ankur Desai Penn State University Meteorology
Dept. ChEAS Meeting VII June 2005
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Goals

• Identify key processes of within-site and
  cross-site variability of carbon dioxide flux in
  space and time with stand-scale observations
• Develop simple multiple flux tower synthesis
  aggregation methods to test the hypotheses that
  stand-scale towers can sufficiently sample
  landscape for upscaling to regional flux
• Parameterize and optimize ecosystem models of
  varying complexity to the region using biometric
  inventory, remote sensing and component flux data
  and test effect of input parameter resolution and
  type on model performance
• Constrain top-down regional CO2 flux using
  multi-tower concentration measurements, and
  simple Eulerian and Lagrangian/stochastic
  transport schema

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ChEAS region and sites

• 13 stand-scale flux towers, 1 tall tower, new
  roving towers

Legend MODIS IGBP 1km landcover
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Interannual variability of NEE

• Interannual variability of NEE is coherent at
  many but not all sites. This does not hold as
  well for GEP or ER

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Intercomparisons and Upscaling
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Flux tower spatial variability

• Stand age is a strong driver of variability
  within specific cover types

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CO2 flux variation drivers

• Canopy height serves as a good proxy for stand
  age
• Canopy height is well correlated to NEE and GEP,
  but not to ER, as one might expect
• The relationship holds for multiple vegetation
  types, especially for GEP
• Thus, remotely sensed measurements of forest
  height, e.g., canopy lidar, could be beneficial
  to regional scaling

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Multi-tower aggregation method

• While mature hardwood sites are dominant in the
  40-km radius around WLEF region according to FIA
  and 30-m Wiscland data, wetlands and young and
  intermediate aspen sites cannot be ignored

• Simple method used to aggregate flux tower data
  using land cover and FIA data and tower derived
  parameters

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Multi-tower aggregation results

• Multi-tower synthesis aggregation and footprint
  weighted decomposition results for 40-km radius
  are in very close agreement
• Tall tower has greater ER and smaller NEE
  compared to bottom-up methods

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Multi-tower aggregation results
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Regional flux comparisons

• Convergence in regional estimates of CO2 flux
• These estimates are larger than tall tower flux
• Reasons remain elusive

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Ecosystem modeling

• Competing effects of ecosystem model complexity
  and data assimilation / parameterization in the
  upper Midwest
• Examine two models
• BIOME-BGC stand-scale single-layer BGC model
• ED gap-scale model with explicit
  disturbance/mortality/size
• Assimilate ChEAS area ecosystem information
• Remotely sensed land cover, phenology
• FIA stand age distribution, harvest rates, land
  use
• Component flux optimized PFT rates and
  decomposition rates
• Compare model to tall tower and other regional
  estimates
• Compare to multi-tower aggregation, footprint
  decomposition, ABL budget based methods
• Assess impact of model complexity
• Assess role of data optimization, scale, density
• Predict future changes in regional CO2 flux

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Biome-BGC

• Daily time step relatively simple
  biome/stand-scale ecosystem process model
• Stand age and disturbance can be externally
  prescribed
• Initial work here will be used with more
  elaborate scaling for currently ongoing roving
  tower/scaling project by F.A. Heinsch, U. Montana

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Ecosystem Demography model

• Moorcroft, P. R, G. C. Hurtt, S. W. Pacala, A
  method for scaling vegetation dynamics the
  ecosystem demography model (ED), Ecological
  Monographs, 71, 557-585, 2001.
• Explicit consideration of stochastic disturbance
  events, effect of stand age and mortality

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Remote-sensing

• IKONOS 4-m 10x10 km around tall tower
  (courtesy B. Cook)
• Legend

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Spatial resolution and land cover

• Land cover in region is highly sensitive to
  resolution due to large number of small area
  cover types, especially wetlands
• Land cover change is also important due to
  logging and disturbance

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Incorporation of FIA data

• FIA statistics on age, biomass, mortality and CWD
  can be used to prescribe model parameters

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Multi-tower ABL budget

• Simple Eulerian models with 1-D ABL depth model
  and NOAA aircraft CO2 profile data can be used to
  test ring of tower validity and provide
  confidence for inversion

• More sophisticated stochastic Lagrangian model,
  similar to COBRA, to be developed to test methods
  to assimilate multi-tower synthesis data

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Conclusions

• Coherent variations in time for NEE across most
  sites but not as much for ER and GEP
• Stand age, canopy height, cover type can explain
  large proportion of cross-site variation
• Convergence is seen in bottom-up and top-down
  regional flux estimates but they generally
  differ from tall-tower flux, except when
  reweighted for footprint contribution
• Ecosystem models to be run this summer
• Resolution of remotely sensed data can have large
  impact on scaling results in heterogeneous region
  
• Simple budget methods with ring of towers
  suggests that more complex inversions will work
• Multi-tower work here complements single-tower
  footprint and budget work of W. Wang and
  tall-tower modeling of D. Ricciuto

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Some publications

• Cook, B.D., Davis, K.J., Wang, W., Desai, A.R.,
  Berger, B.W., Teclaw, R.M., Martin, J.M.,
  Bolstad, P., Bakwin, P., Yi, C. and Heilman, W.,
  2004. Carbon exchange and venting anomalies in an
  upland deciduous forest in northern Wisconsin,
  USA. Agricultural and Forest Meteorology,
  126(3-4) 271-295 (doi10.1016/j.agrformet.2004.06
  .008).
• Desai, A.R., Bolstad, P., Cook, B.D., Davis, K.J.
  and Carey, E.V., 2005. Comparing net ecosystem
  exchange of carbon dioxide between an old-growth
  and mature forest in the upper Midwest, USA.
  Agricultural and Forest Meteorology, 128(1-2)
  33-55 (doi 10.1016/j.agrformet.2004.09.005).
• Desai, A.R., Noormets, A., Bolstad, P.V., Chen,
  J., Cook, B.D., Davis, K.J., Euskirchen, E.S.,
  Gough, C.M., Martin, J.M., Ricciuto, D.M.,
  Schmid, H.P., Tang, J. and Wang, W., submitted.
  Influence of vegetation and climate on carbon
  dioxide fluxes across the Upper Midwest, USA
  Implications for regional scaling, Agricultural
  and Forest Meteorology.
• Heinsch, F.A., Zhao, M., Running, S.W., Kimball,
  J.S., Nemani, R.R., Davis, K.J., Bolstad, P.V.,
  Cook, B.D., Desai, A.R., et al., in press.
  Evaluation of remote sensing based terrestrial
  producitivity from MODIS using regional tower
  eddy flux network observations, IEEE Transactions
  on Geosciences and Remote Sensing.

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Ph.D. plans

• May ChEAS meeting, fieldwork
• Jun-Aug Ecosystem model parameterization and
  runs, potential return visits to Montana/Harvard
  for model work
• July-Aug Top-down Lagrangian ABL budget
• Jun-Oct ChEAS special issue paper reviews
• Sep pre-dissertation defense committee meeting
• Sep-Dec dissertation writing, redo footprint
  model, add 2004 tower data to 1st chapter,
  finalize multi-tower aggregation chapter, apply
  to jobs
• Sep present at International CO2 conference,
  Boulder, CO
• Oct ChEAS fall fieldwork
• Oct-Nov present at Ameriflux, Boulder, CO
• Dec present at AGU, San Francisco, CA
• Dec-Feb finish dissertation, send to committee
  and to format review
• Jan present ABL research at AMS, Atlanta, GA?
• Mar defend dissertation!
• Mar-Sep submit final model results for
  publication, party, travel
• Fall 2006 post-doc?

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Thank You
ChEAS
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