O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 1 Carbon Cycle Modeling Terrestrial Ecosystem Models W.M. Post, ORNL Atmospheric Measurements

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OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Carbon Cycle Modeling

Terrestrial Ecosystem Models

W.M. Post, ORNL

Atmospheric Measurements and Models

S. Denning, CSU

Global and Regional Inferences from Monitoring

C.D. Keeling, SIO

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Terrestrial Modeling

Objectives Progress New Directions Future Challenges

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Terrestrial Modeling - Objectives

Quantify CO2 exchanges with the atmosphere

Project how terrestrial CO2 exchanges will change in the future

Provide estimates of trace gas sources and sinks for use with atmospheric models or in Earth System Models

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Terrestrial Modeling - Progress

Photosynthesis, evapotranspiration - detailed characterization, Biochemical models Light-use efficiency models

Soil organic matter decomposition – robust representation, model/data comparisons at different temporal scales Multicompartment structure C, N and nutrient dynamics

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Terrestrial Models - Progress (cont.)

Model intercomparison projects CMEAL, VEMAP, CCMLP

Model - data comparison projects Individual experimental and monitoring sites AmeriFlux modeling activity Ecosystem Model-Data Intercomparison

(EMDI)

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MAESTRA Simulations vs. Eddy Covariance Measurements – Duke FACE (Luo et al. 2001)

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Global Biogeochemical Simulations

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Regional Light-Use Efficiency Model Calculations

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Model - Experimental Observations Interaction

Detailed process level description allows: Incorporation of new experimental findings Model comparison to experimental and field

measurements Identify measurements and processes that

suggest additional hypotheses

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North America Historical Simulation

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Local Time (Hours)

0 5 10 15 20

CO

2 E

xcha

nge

Rat

es ( m

ol m

-2 s

-1)

-30

-20

-10

0

10

Effects of Mt Pinatubo perturbation on CO2 exchanges

on a clear day in Oak Ridge, Tennessee

Global PAR: -3%Direct PAR: -30%Air and soil temperature: -0.5oC

Normal

Perturbed

Ecosystem respiration

GPP

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Pure diffuse or direct PAR (mol m-2 s-1)

0 500 1000 1500

Diff

use

to d

irect

canopy

q

uantu

m y

ield

ratio

1

2

3

4

Tallgrass prairie

Aspen forest

Scots pine forest

Winter wheat

Mixed deciduousforest

Increase in Photosynthesis with Diffuse Radiationfor Different Ecosystems

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Role of clouds, aerosols in global carbon cycle

• Diffuse radiation results in higher light use efficiencies by plant canopies

• Diffuse radiation has a much less tendency to cause canopy photosynthetic saturation

• Under a turbid atmospheric environment caused by natural events such as volcanic eruptions, canopy photosynthesis can be enhanced if part of the reduction in direct solar radiation is converted into diffuse radiation

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Terrestrial Modeling - New Directions

Additional processes Phenology Allocation

Biogeography shifts Land-use change

Inventories and surveys Remote sensing

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Terrestrial Modeling - Challenges

Continue to increase spatial and temporal resolution improves process representation of regional

and global spatial variation allows use of wider range of observations for

tests of consistency/validation

Data assimilation Parameter estimation Initial condition or state estimation

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North America Carbon Cycle (GTEC)

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Level of NEP Depends on Initial Conditions

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Initial Condition Strategy

Model spin-up with conditions “typical” of pre-simulation period

Adjust initial conditions with simulation using available historical observations (land-use statistics, age-class structure, remote sensing)

Use numerical weather prediction like data assimilation techniques to continually adjust model states to be consistent with “real time” monitoring information (Ameriflux, Globalview, MODIS, FIA, etc.)

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Terrestrial Modeling - Summary

Biogeochemical process understanding results in: Improving generality of terrestrial models Improving representation of interactions and feedbacks

between CO2, radiation, climate, nutrient cycles

Terrestrial models are increasing in spatial and temporal resolution

Integration with atmospheric models will be critical for identifying terrestrial C sources and sinks

Documents

O AK R IDGE N ATIONAL L ABORATORY U. S. D EPARTMENT OF E NERGY 1 Carbon Cycle Modeling Terrestrial Ecosystem Models W.M. Post, ORNL Atmospheric Measurements