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Evaluation of land model simulations across multiple sites and multiple models: Results from the NACP site-level synthesis effort. Peter Thornton 1 , Gautam Bisht 1 , Dan Ricciuto 1 , NACP Site-Level Synthesis Participants

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Evaluation of land model simulations across multiple sites and multiple models:Results 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

sponsors
Sponsors
  • NASA Terrestrial Ecology Program
  • DOE, Office of Biological and Environmental Research, Climate and Environmental Sciences Division, Terrestrial Ecosystem Science Program
premise
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
analysis setting
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
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

12 Models and 13 Sites
diurnal cycle of gpp us dk3
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

findings 1
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
findings 2
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
findings 3
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?
findings 4 underway
Findings: 4 (underway)
  • Introducing transient forcing (disturbance, rising atmospheric CO2, changing N deposition) seems to improve estimate of decadal-scale NEE
    • Doesn’t seem to change conclusions obtained from steady-state simulations
    • This is the most critical flux for evaluation of long-term climate-carbon cycle feedbacks
conclusions
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.
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