Variability in Terrestrial Carbon Sinks over Two Decades. Part I: North America

Abstract

Seventeen years (1982?98) of net carbon flux predictions from a simulation model based on satellite observations of monthly vegetation cover have been analyzed. The NASA?CASA model was driven by vegetation cover properties derived from the Advanced Very High Resolution Radiometer and radiative transfer algorithms that were developed for the Moderate Resolution Imaging Spectroradiometer (MODIS). It is found that although the terrestrial ecosystem sink for atmospheric CO2 on the North American continent has been fairly consistent at between +0.2 and +0.3 Pg C yr?1, high interannual variability in net ecosystem production (NEP) fluxes can be readily identified at locations across the continent. Five major areas having the highest variability were detected: 1) along the extreme northern vegetated zones of Canada and Alaska, 2) the northern Rocky Mountains, 3) the central-western U.S. Great Plains and central farming region, 4) across the southern United States and Mexico, and 5) in coastal forest areas of the United States and Canada. Analysis of climate anomalies over this 17-yr time period suggests that variability in precipitation and surface solar irradiance could be associated with trends in carbon sink fluxes within regions of high NEP variability.