- Related Research Areas
- Carbon Cycle & Ecosystems
One of the major challenges of the North American Carbon Program is to develop an integrated approach to characterizing regional carbon budgets. Net ecosystem exchange (NEE), the net biologically driven exchange of CO2 between terrestrial ecosystems and the atmosphere, is arguably the single-most important variable that should be measured and modeled because it directly influences intra-annual and inter-annual variation in the CO2 concentration of the atmosphere. The proposed research will generate daily and annual estimates of gross ecosystem exchange and NEE over North America at the 1 km spatial resolution for the MODIS era using spatially distributed models. We will investigate sources of variation and uncertainty in our estimates associated with interannual variation in climate, with how disturbance history is characterized, and with the form of the spectral data used in the scaling procedure. The approach will use a combination of prognostic and diagnostic carbon cycle models, with a focus on satellite-driven diagnostic models developed with previous NASA support. There will be heavy reliance on eddy covariance flux tower observations for model parameter optimization and validation, and the core tower sites will include 8 sites previously used for validation of MODIS Land Products in the NASA-supported BigFoot Project. Disturbance history will be prescribed with data from the LEDAPS Project and the MODIS Burned Area Product. Alternative FPAR (fraction of photosynthetically active radiation absorbed by the vegetation canopy) products, including those from the MODIS, SeaWiFS, VEGETATION, and MERIS sensors, will be tested along with the MODIS EVI product at 250, 500, and 1000 m resolution. We will evaluate our continental NEE estimates by comparisons to continental scale estimates of NEE from an inversion approach based on observations of CO2 concentration (NOAA’s CarbonTracker). Our fluxes will also be input to CarbonTracker and discrepancies between observed and predicted CO2 concentrations will be used to evaluate alternative model algorithms and inputs (e.g. MODIS vs. SeaWiFS FPAR). By including satellite-based information on previous disturbance, and model algorithms that account for increased heterotrophic respiration after disturbances, our approach addresses a major gap in the current NACP effort to quantify the carbon budget of North America. By including satellite-based information on vegetation phenology, along with distributed climate data, the proposed work will significantly enhance our ability for attribution, i.e. distinguishing the relative roles of net primary production and heterotrophic respiration in accounting for interannual variation in NEE. Because quantifying the terrestrial carbon sink in North America is of policy significance in relation to addressing the climate change issue, this research contributes to the NASA strategic goal of advancing scientific understanding of Earth and meeting societal needs. It will further the NASA research objective of improving carbon cycle models, and results will inform the next NACP assessment of the state of the carbon cycle.
Project PI: David Turner/Oregon State University
Department of Forest Science Oregon State University Corvallis, Oregon 97331
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