Select from available options to download raster data in GeoTIFF format. The full raster extent can be subset in one of three ways from the Extent button on the map.
When uploading a file or selecting an ecoregion the raster data will be masked outside of the polygon boundary.
Uncertainties that exist in the data products are the results of the estimation and projection methods used for the assessment. Major sources of uncertainties for baseline (1992-2005) data products include assumptions made in structure and parameterization of specific methods and models used in the assessment, relations and integration of these methods and models, and input data availability and quality. The use of land- and climate-change scenarios in the assessment, as part of the carbon modeling, is an additional source of uncertainty for the projected (2006-2050) data products.
Because of the specific methods used in the assessment, the uncertainties are distributed both in temporal and spatial dimensions and they vary by product, location, and specific use. Along the temporal dimensions, mean values of baseline and projection years should be used instead of any given individual years. Along the spatial dimensions, data aggregated to the scale of ecoregions should be used instead of the individual pixels or over relatively small areas of the maps. In addition, the available multiple models and scenarios provide users with ranges of values for a given estimate, which may be used as a means of quantifying the spread of uncertainties.
Methane (CH4) flux is the net rate of methane exchange between an ecosystem and the atmosphere. The Western United States was a methane sink with a flux ranging from −3.1 to −2.9 TgCO2-eq/yr in the baseline period (2001-2005), and little change was projected from 2006 to 2050. Both forests and grasslands/shrublands were methane sinks, and wetlands were methane sources. The methane budget varied regionally; Mediterranean California was a source and the other ecoregions were sinks.
Zhu, Zhiliang, ed., Bergamaschi, Brian, Bernknopf, Richard, Clow, David, Dye, Dennis, Faulkner, Stephen, Forney, William, Gleason, Robert, Hawbaker, Todd, Liu, Jinxun, Liu, Shuguang, Prisley, Stephen, Reed, Bradley, Reeves, Matthew, Rollins, Matthew, Sleeter, Benjamin, Sohl, Terry, Stackpoole, Sarah, Stehman, Stephen, Striegl, Robert, Wein, Anne, and Zhu, Zhiliang, 2010, A method for assessing carbon stocks, carbon sequestration, and greenhouse-gas fluxes in ecosystems of the United States under present conditions and future scenarios: U.S. Geological Survey Scientific Investigations Report 2010–5233, 188 p. (Available from USGS).
The net rates of methane exchange in terrestrial ecosystems in the western United States were estimated using the Paint-By-Number (PBN) model embedded in the USGS General Ensemble Biogeochemical Modeling System (GEMS). PBN only accounts for the impacts of land cover change defined by scenarios according to storylines A1B, A2, or B1 from the Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios (IPCC–SRES). Specifically, the PBN model estimated methane fluxes for different LULC classes and ecoregions using emission factors that were compiled from an extensive review of the literature. Methane fluxes were expressed in carbon dioxide equivalent (CO2-eq) using a factor of 21.