How much carbon is released and taken up by California? We will collect field data (eddy covariance, biomass, ANPP, LAI, C-14), analyze remote-sensing images (ETM+, MODIS), assemble existing data (fire history, land and energy use), develop mechanistic models (ISOLSM, CASA), and build and run a data analysis framework that will produce carbon budgets for California. The budgets will include the sources and sinks associated with natural ecosystems, agriculture, and fossil fuel combustion. The budgets will be spatially resolved for the state, and will include the hourly, daily, seasonal, annual and interannual carbon exchanges from March 2000 to December 2007.
How much confidence should we have in our C budgets? We will estimate uncertainties for the input data by comparison with independent data. We will propagate these uncertainties by Monte Carlo simulation to determine confidence intervals for the budgets. We will also test the budgets by comparing the regional pattern of atmospheric CO2 and CO concentration predicted from the budgets with observed CO2 and CO concentrations.
How do our results compare with previous budgets? The Environmental Protection Agency (EPA) has created annual C budgets for the US since 1997 for reporting to the United Nations Framework Convention on Climate Change. These budgets overlap markedly with the NACP’s goals. We will compare our results for California with budgets that were created by the California Energy Commission (CEC) using the EPA protocol. Our focus on mechanistic controls, and on the C exchanges at a range of time scales, goes well beyond the EPA’s and CEC’s scope. Nonetheless, we feel it is important to relate our results to the EPA’s and CEC’s parallel efforts.
How much, and why, does California’s carbon balance vary from year to year? We will use our budgets to quantify the year-to-year differences in California’s CO2 exchange. We will consider the importance of interannual precipitation variability, fire emission, recovery from disturbance (fire, logging, and disease), stand thickening with fire suppression, land-use change, and agriculture. We hypothesize that variability in climate and fire cause large year-to-year differences in CO2 exchange by California’s ecosystems.
What processes control the CO2 concentration of air leaving California? We will use our budgets and an atmospheric tracer model (MM5) to explore the effects of the various carbon sources and sinks on the atmosphere’s CO2 concentration. We will partition the enrichment or depletion of CO2 in air leaving California into the effects of fossil fuel emission and the exchanges with short-lived and long-lived ecosystem pools. We hypothesize that the imprint of exchanges with short-lived ecosystem pools (sugars, leaves, fine roots) and fossil fuel emissions dominate the regional patterns of CO2 concentration. As a result, inversions of regional CO2 concentration are unlikely to provide much information about carbon uptake by long-lived pools (wood, soil).
Where do California’s CO2 emissions go? We will use the tracer model to determine how California’s carbon exchanges affect the concentration of CO2 at larger scales. We will focus on better understanding the magnitude, composition, and flow direction of the carbon-enriched (or depleted) plumes of air originating from California’s cities and ecosystems. We will determine whether covariances between extreme events (e.g., fires) and circulation (e.g., strong offshore flow during Santa Ana winds) decouple some components of California’s carbon budget from the North American air mass.