The data set consists of a southern African subset of the "Global Patterns of Carbon Dioxide Emissions from Soils on a 0.5 Degree Grid Cell Basis" (Raich and Potter 1996). Data files are provided in ASCII GRID format.
This source database contains global, spatially explicit (0.5-degree grid cells) and temporally explicit (monthly and annual) model output of soil CO2 emissions. The calculated emissions include the respiration of both soil organisms and plant roots.
The model (model B) used for these calculations is described in Raich and Potter (1995). The model is based on a stepwise linear multiple regression of 977 individual aggregated records of geographically referenced data on daily and/or monthly rates of CO2 flux rates from intact soils, temperature, precipitation, potential evapotranspiration, vegetation type, soil moisture status, and organic carbon and nitrogen contents of soil. These data points represent grid cells from every continent except Antarctica. Temperature and soil moisture status, as predicted by precipitation, were the only variables significantly correlated with soil CO2 efflux. Temperature and precipitation were, therefore, used as driving variables. The remaining model parameters for the mechanistic aspect of the model are (1) the soil CO2 efflux rate when temperature is zero and moisture not limiting, (2) the temperature coefficient and (3) the half-saturation coefficient of the precipitation function. These were obtained by Raich and Potter (1995) using least squares estimates.
To prevent extrapolation of the model beyond the range of observed temperatures, (1) soil CO2 fluxes were presumed to be zero at average monthly air temperatures less than -13.3 degrees Celsius, and (2) for all temperatures greater than 33.5 degrees Celsius, soil CO2 fluxes were set equal to the rate predicted at 33.5 degrees Celsius.
Raich and Potter (1995) evaluated their model predictions against previously published annual soil respiration rates from specific locations and with published predictions by an annual model (Raich and Schlesinger 1992) through linear regressions of predicted versus observed (or previously published predicted) soil emissions. Correlation coefficients were close to 0.5, intercepts not significantly different from zero and slopes not significantly different from one, indicating that the reliability of the predictions was not diminished by the monthly timescale and that the model provides quantitatively meaningful estimates of annual soil emissions.
More information can be found at: http://cdiac.esd.ornl.gov/ndps/db1015.html. Please note that there is an update to DB1015. "Interannual Variability in Global Soil Respiration on a 0.5 Degree Grid Cell Basis" is now available with enhanced documentation as numeric data package NDP-081 (http://cdiac.ornl.gov/epubs/ndp/ndp081/ndp081.html). Specifically, DB1015 used long-term climate data as model input while NDP-081 utilizes new climate and land cover data files.
Cite this data set as follows:
Raich, J. W., and C. S. Potter. 2002. SAFARI 2000 Annual CO2 Emissions from Soil, 0.5 Deg-Grid (Raich and Potter). Data set. Available on-line [http://www.daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. doi:10.3334/ORNLDAAC/644.
Raich, J. W., and C. S. Potter. 1995. Global patterns of carbon dioxide emissions from soils. Global Biogeochemical Cycles 9(1):23-36.
Raich, J. W., and C. S. Potter. 1996. Global Patterns of Carbon Dioxide Emissions from Soils on a 0.5 Degree Grid Cell Basis. ORNL/CDIAC DB-1015 (3-1996). Carbon Dioxide Information Analysis Center, U.S. Department of Energy, Oak Ridge National Laboratory, Oak Ridge, Tennessee, U.S.A.
Raich, J. W., C. S. Potter, and D. Bhagawati. 2003. Interannual Variability in Global Soil Respiration on a 0.5 Degree Grid Cell Basis. ORNL/CDIAC NDP-081. Carbon Dioxide Information Analysis Center, U.S. Department of Energy, Oak Ridge National Laboratory, Oak Ridge, Tennessee, U.S.A.
Raich, J. W., and W. H. Schlesinger. 1992. The global carbon dioxide flux in soil respiration and its relationship to vegetation and climate. Tellus 44 B:81-99.
For information on preparation of this subset, parameter/variable names, variable description/definition, units of measurement, and data file format see this companion file http://daac.ornl.gov/daacdata/safari2k/soils/soil_respiration_gridded/comp/raich_potter_grid_co2.pdf.