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

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?

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

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

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.

Biome-BGC vs Flux (Evergreen Needleleaf Forest)

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

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.

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

NASA-CASA Model Prediction of North American Carbon Sink Fall AGU ‘01 B52B-03 “The North America Carbon Sink from 1982-1998” 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. -100 -50 0 +50 +100 -100 -50 0 +50 +100 g C m-2 yr -1 Smoothed Annual Temperature 30o - 60o N. America

BOREAS

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

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

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

Source: Potter, C. , S. Klooster, et al Source: Potter, C., S. Klooster, et al. 2007, 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

Agricultural Management Impacts on Soil Carbon Storage (Download available at http://geo.arc.nasa.gov/sge/casa/cquestwebsite/ ) References for the Data Set: Eve, M.D., M. Sperow, K. Paustian, and R. Follett. 2002. National-scale estimation of changes in soil carbon stocks on agricultural lands. Environmental Pollution, 116: 431-438. USDA National Resources Inventory (NRI): http://www.nrcs.usda.gov/technical/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

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

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.