1. Continental Modeling and Analysis of the North American Carbon Cycle
CHRISTOPHER POTTER and RAMAKRISHNA NEMANI,
NASA Ames Research Center
U.S. Investigators NACP Meeting
January 23, 2007

2. Synthesis Questions
Which ecosystems types and/or regional land cover areas in North America have been the largest contributors to annual net carbon fluxes for the continent over the past 5-10 years?
What are the principal sources of uncertainty in the estimate(s) from Question 1 above?

3. Ecosystem Modeling & Remote Sensing Approaches
Land Cover Products
Process Model
Biomass
Pools
Elevation
NPP/Rh Flux .
User Defined Output
Region of Interest
Time Frame
Biophysical
Management
Climate Scenario
Outputs: landscape-to continental scale predictive maps of above and below ground distributions of sequestered carbon for different climate scenarios .
Climate data
Inputs include continental-scale
land cover, EVI, FPAR, LAI, elevation, soils, and climate data …
Carbon Sequestration Predictions
Inventory and Analysis Data
Tower Data
Multi-scale Validation Information

4. Interannual Variability in MODIS NPP Carbon Fluxes
Source: Maosheng Zhao, Steve Running, et al. (2006)

6. Compared to inventory data, the default MODIS algorithm tends to underestimate NPP for the northern hardwood forests and overestimates NPP for coniferous and mixed forests
-- But can be corrected by modeling soil moisture limitations.

7. Biome-BGC vs Flux (Evergreen Needleleaf Forest)

8. Terrestrial Carbon Cycle from Biome-BGC (1950-2003)
GPP (gC/m2/y)
GPP CV (%)
NEE (gC/m2/y)
NEE σ

9. Post et al. (2006): The impact of ENSO cycles on NEP of North America terrestrial ecosystems indicated by the simulations of GTEC.
During the unusual El Niño of the early 1990’s when Mount Pinatubo erupted, there is a large increase in the simulated North America carbon sink.
Maps of the modeled NEP summed for X years indicate an increased carbon uptake by nearly all terrestrial ecosystems with the largest changes occurring in the eastern and boreal forests.

10. NASA-CASA Simulation Model
EOS Satellite Product Inputs
(a) Daily Soil Moisture Balance and
Irrigation of Cultivated Land
(b) Plant Production and
Nutrient Mineralization
(c) Fertilizer Application and
Trace Gas Emissions
FPAR/EVI
CO2
Air Chemistry
Model
PPT
TEMP
PPT
PET
SOLAR }
PET
NPP
NEP
Biomass
M 0
M 1
M 2
M 3
M 0
M 1
M 2
M 3
M 0
M 1
M 2
M 3
Soil Surface
Soil
Profile
Layers
Freeze/Thaw
Fertilizer N
Leaf Litter
f(N form)
f(Application)
Wood Litter
Root Litter
f(pH)
f(Temp)
f(Water)
Heat &
Water
Flux
Microbes
Soil Organic
Matter
f(Temp)
f(Water)
f(Lit q)
CO2 (CH4)
N2O
(NH3 & NO)
f(Lit q)
Crop/Grass Shrub Tree
LAND COVER TYPES
Soil N

11. NASA-CASA Model Prediction of North American Carbon Sink
Fall AGU ‘01 B52B-03 “The North America Carbon Sink from ”
1996
1997
1998
0.14 Pg C sink
0.39 Pg C sink
0.32 Pg C sink
C Source
C Sink
Summary:
Since 1982, the terrestrial ecosystem sink for atmospheric CO2 in North America has been fairly consistent (at ca. 0.3 Pg C per year), except during relatively cool periods.
(b) Regional warming has had the greatest impact on high latitude (boreal) forest sinks for atmospheric CO2 in North America.
g C m-2 yr -1
Smoothed Annual Temperature
30o - 60o N. America

12. BOREAS

13. NASA-CASA Model Prediction of U.S. Annual NEP Flux
Potter et al. (submitted); Estimated using MODIS 8-km EVI Products

14. Terrestrial Carbon Budget of the Continental United States All numbers are in units of Pg C for the late 1990s (Potter et al., 2006)

15. NASA-CASA Model Prediction of Surface Soil C Pools
Potter et al. (2006); Does not include soil C stored below 30 cm depth

16. Source: Potter, C. , S. Klooster, et al
Source: Potter, C., S. Klooster, et al , Methane emissions from natural wetlands in the United States: Satellite-derived estimation based on ecosystem carbon cycling, Earth Interactions (in press). Estimated total U.S. annual emissions = 5 Tg CH4

17. Agricultural Management Impacts on Soil Carbon Storage
(Download available at )
References for the Data Set:
Eve, M.D., M. Sperow, K. Paustian, and R. Follett National-scale estimation of changes in soil carbon stocks on agricultural lands. Environmental Pollution, 116:
USDA National Resources Inventory (NRI):
NASA/USDA Carbon Cycle Science project: CO2 Fluxes Between Agricultural Lands and the Atmosphere: Towards More Complete Accounting by Integrating Remote Sensing with Simulation Modeling PI: Stephen Ogle, Colorado State University

19. Source: T. West, et al. (2006)

20. Observations and Recommendations
Numerous regional-to-global modeling approaches show similar patterns in predicted NPP and carbon cycle variations over the U.S. continental region.
Areas of the contiguous U.S. that are contributing the most (in magnitude and variability) to the annual carbon cycle are in the Southeast, Gulf Coast, and Mountain West regions.
Uncertainties on which NACP Investigators should focus most of their efforts are the roles of major disturbances (drought, wildfire, and hurricane) and forest management practices in these three above-named regions of the U.S.