Using Biophysical Models to Ask (and Answer) Questions About Biosphere-Atmosphere Interactions

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Using Biophysical Models to Ask (and Answer)
Questions About Biosphere-Atmosphere Interactions

• Dennis Baldocchi
• Alexander Knohl
• James Dorsey
• Biometeorology Lab
• University of California, Berkeley

ILEAP Meeting Boulder, CO Jan, 2006
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ILEAPS Paradigm
Isotopicexchange
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Sub-Grid VariabilityWhat are Errors in ET
Scaling?
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Answering Questions with Models

• Diffuse Radiation
• Light Use Efficiency
• Isoprene emission
• Water Use Efficiency
• Stable Isotopes
• Sub-Grid Parameterization, Energy Balance Closure
  and Scaling
• Insights from a 2-D, Wet DaisyWorld

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CANVeg MODEL
Physiology
Photosynthesis
Stomatal Conductance
Transpiration
Micrometeorology
Leaf/Soil Energy Balance
Radiative Transfer
Lagrangian Turbulent Transfer
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Key Attributes of CanVeg

• Seasonality
• Leaf Area Index
• Photosynthetic Capacity (Vcmax)
• Model parameters based on Site Measurements and
  EcoPhysiological Rules and Scaling
• Stomatal Conductance scales with Photosynthesis
• Jmax and Rd scale with Vcmax
• Multilayer Framework
• Computes Fluxes (non-linear functions) on the
  basis of a leafs local environment
• Considers
• Sun and Shade Leaf Fraction
• Leaf Clumping
• Leaf Inclination Angle
• Non-local Turbulent Transport and
  Counter-Gradient Transfer

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CO2 Flux Model Test Hourly to Annual Time Scales
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Another Form of Model Testing Reproducing
Spectral Fidelity
Baldocchi et al, 2001 Ecological Modeling
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Results and Discussion
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How Sky Conditions Affect Net Carbon Exchange
(NEE)? Data
Baldocchi, 1997 PCE
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CO2 Flux and Diffuse RadiationData from
AmeriFlux
Niyogi et al., GRL 2004
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Volcanoes, Aerosols NEE
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How do Changes in Diffuse Radiation affect Canopy
Fluxes? Case Mt Pinatubo Explosion, 10 of
beam -gt diffuse
direct beam
Solar radiation W m-2
Year of Mt. Pinatuboeruption
diffuse
Solar elevation angle
Gu et al, 2003, Science
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Canopy Photosynthesis and Aerosols Impact on
Daily Annual Scales, I
increase diffuse by 10 beam 1527 gC m-2 y-1
Canopy Photosynthesis may increase by 50 gC m-2
y-1
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Conventional WisdomMore Light Absorption with
Diffuse Radiation
WHY?
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More Efficient Use of Light by Shade Leaves?
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vpd is Correlated with Diffuse Fraction Less
Physiological Stress (?)
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(No Transcript)
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Isoprene and Diffuse Radiation
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Stable Isotope Discrimination and Diffuse Light
Preference of photosynthesis for light 12CO2 vs.
heavier 13CO2
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Autocorrelations among Ci/Ca, vpd and
diffuse/Total
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Water Use Efficiency (A/T) and diffuse light
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Simple Model suggests A/T decreases with D or
Ci/Ca
e.g. A/T of C4 gt C3
But Complex feedbacks need to be considered!
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How Do Changes in vpd and Ci/Ca conspire to
affect A/T?
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In toto (considering coupled energy balance
feedbacks) A/T increases with Ci/Ca
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Sub-Grid Variability Lessons Derived from Wet
DaisyWorld
Latent Heat Exchange Map
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Eddy covariance footprints and ecosystem
representativeness
Footprint representation
Newly developed 3d Lagrangian stochastic
footprint model was run for a 1 m canopy and 3 m
measurement height. Half a million trajectories
were integrated to calculate the source
probability density.
The footprint calculation was run using the same
grid geometry as the DaisyWorld simulation to
allow convolution of the results. The EC tower
was placed in different locations in the
simulated ecosystem, and the EC system's view of
the ecosystem was calculated.
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Eddy covariance footprints and ecosystem
representativeness
Each histogram shows 500 separate tower locations
within the simulated ecosystem.
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Errors in ET Scaling
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Conclusions

• Biophysical Model aids in understanding the
  impact of diffuse light on photosynthesis,
  isoprene emission, water use efficiency and
  stable isotope discrimination
• A cellular automata, energy balance model shows
  that spatial averaging of energy balance drivers
  can produce huge errors in grid-scale energy
  fluxes and can explain lack of energy balance
  closure

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Acknowledgements

• Funding
• NASA, DOE/TCP, NIGEC/WESTGEC
• Diffuse Light and Carbon
• Lianhong Gu
• Isoprene
• Peter Harley, Jose Fuentes, Dave Bowling, Russ
  Monson Alex Guenther
• 13C Isotopes
• Dave Bowling, Russ Monson
• Footprints DaisyWorld
• Monique Leclerc, Tess Krebs, Joon Kim, Peter
  Levy, HaPe Schmid, Brian Amiro

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Canopy Photosynthesis and Aerosols Impact on
Daily Annual Time Scales, II
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Role of Diffuse Light on Water Use Efficiency A/E
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Baldocchi et al, 2005 Tellus
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Quantifying Sources and Sinks

• Biology
• Leaf area density, a(z)
• internal conc, Ci
• stomatal resistance, rs
• Physics
• Boundary layer resistance, rb
• Scalar conc, C(z)

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Partial ExplanationFiso is very sensitive to
Leaf Temperature, which changed little in
response to the imposed direct to diffuse
partitioning