Evaluation of land model simulations across multiple sites and multiple models: Results from the NACP site-level synthesis effort

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Evaluation of land model simulations across
multiple sites and multiple modelsResults from
the NACP site-level synthesis effort

• Peter Thornton1, Gautam Bisht1, Dan Ricciuto1,
  NACP Site-Level Synthesis Participants
• 1 Oak Ridge National Laboratory, Environmental
  Sciences Division and ORNL Climate Change Science
  Institute

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Sponsors

• NASA Terrestrial Ecology Program
• DOE, Office of Biological and Environmental
  Research, Climate and Environmental Sciences
  Division, Terrestrial Ecosystem Science Program

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Premise

• Models can and should serve as tools for the
  integration and synthesis of our best
  understanding and knowledge
• Models can and should provide testable
  (falsifiable) hypotheses
• Through model-data synthesis efforts, those
  hypotheses can and should be tested, and
  discarded or improved when confidence is shown to
  be low

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Analysis setting

• Subset of sites and models from full NACP
  site-level synthesis effort
• Forest sites (evergreen and deciduous)
• Range of climates
• Models that include diurnal cycle
• Carbon, sensible heat, latent heat fluxes
• Diurnal cycle, seasonal cycle, interannual
  variability, long-term mean
• Influence of steady-state vs. transient forcings

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12 Models and 13 Sites

• CAN-IBIS
• CNCLASS
• CLM-CN
• ECOSYS
• ED2
• ISOLSM
• LOTEC
• ORCHIDEE
• SIB
• SIBCASA
• SSIB2
• TECO

• CA-Ca1 Campbell River
• CA-Oas Old aspen
• CA-Obs Old black spruce
• CA-Ojp Old jack pine
• CA-Qfo Mature black spruce
• CA-TP4 Turkey Point
• US-Dk3 Duke Forest pine
• US-Ha1 Harvard Forest main
• US-Ho1 Howland main
• US-Me2 Metolius intermediate
• US-MOz Missouri Ozark
• US-NR1 Niwot Ridge
• US-UMB U Michigan Bio Stn

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Diurnal cycle of GPP US-Dk3
Mean diurnal cycle for June-July-August, y-axis
units umol/m2/s, x-axis is half-hour time step.
Results from steady-state simulations
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Diurnal cycle of GPP CA-Obs
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Diurnal cycle of GPP US-UMB
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Diurnal cycle of NEE CA-Oas
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Diurnal cycle of NEE US-Ha1
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Diurnal cycle of NEE US-Dk3
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Diurnal cycle of NEE CLM-CN
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Seasonal cycle of CLM-CN US-Ha1
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Findings 1

• Time-scale of N-limitation mechanism in CLM-CN is
  wrong.
• Evident at both diurnal and seasonal
• Original hypothesis that plants respond to N
  availability on sub-daily time scale should be
  rejected
• Introducing new mechanism to buffer N
  availability in time

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Findings 2

• Evaluation of LE suggests that current basis for
  estimation of stomatal conductance in CLM-CN is
  reasonable
• This result should be revisited once new N
  storage mechanism is added

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Findings 3

• CLM-CN is very sensitive to fine root leaf
  allocation patterns
• Difficult measurement
• Likely candidate parameter for data assimilation
• Evidence emerging from global-scale studies and
  comparison to root turnover data that model fine
  root longevity needs to be modified
• Other models sensitive to this as well?

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Findings 4 (underway)

• Introducing transient forcing (disturbance,
  rising atmospheric CO2, changing N deposition)
  seems to improve estimate of decadal-scale NEE
• Doesnt seem to change conclusions obtained from
  steady-state simulations
• This is the most critical flux for evaluation of
  long-term climate-carbon cycle feedbacks

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Conclusions

• Approach has proved very useful in identifying
  strengths and weaknesses in CLM-CN
• This kind of critical evaluation across multiple
  models provides a path forward for improved
  future model generations
• Improving modelers ability to know what to ask
  for from observationalists and experimentalists.