An assessment of vegetation fire in Africa (1981-1991):: Burned areas, burned biomass, and atmospheric emissions

This paper presents the first published time series of burned area maps of Africa, covering an 8 year period, 1981-1983 and 1985-1991. These maps were derived from the analysis of the advanced very high resolution radiometer (AVHRR) global area coverage (GAC) images at 5 km resolution. The burned area maps for the period 1985-1991 were used with biomass density and burning efficiency figures, to estimate the quantity of burned biomass during this 6 year period. Emission factors were further used to estimate the trace gas and aerosol emissions produced by vegetation fires. Biomass density was estimated based on values found in the literature and on the accumulated normalized difference vegetation index (NDVI) as derived from the remote sensing images. Burning efficiency was assessed with a dryness index that was based on the relative greenness index (RGI), also derived from the NDVI. Average emission factors were retrieved from the literature. The uncertainties in the burned area, biomass density, combustion efficiency, and emission factors were considered, with a total error of 51% for the burned biomass and 58% for the emission estimates. The results obtained for the burned biomass in Africa were compared with other values found in the literature and showed values lower by a factor of 1.1-3.3. The annual burned biomass from vegetation fires in Africa on average was estimated between 704 and 2168 Tg. In the same way, the atmospheric emissions on average ranges are as follows: CO2 (990-3726 Tg), CO (40-151 Tg), CH4 (1.2-4.4 Tg), NOx (2.8-10.6 Tg), and PM (< 2.5 mu m) (3.3-12.4 Tg).