Estimating carbon emissions from African wildfires

Africa is a continent dominated by fire. Vegetation fires, occurring naturally or human-ignited as a land management practice, have a long history in the continent's savannah ecosystems. These fires contribute substantially to the total carbon emissions (e.g. as CO2, CO, CH4, Volatile Organic Compounds, Black Carbon) over large parts of the continent. Many recent attempts to assess the total area burnt and the amount of carbon emitted have been based on satellite remote sensing of active fires. To calculate emissions, the burned area estimates are typically multiplied with emission factors that are specific for each compound and land cover type, or used to distribute output from a biogeochemical model spatially. We developed a technique for estimating carbon emissions using a modelling approach to scale burned area estimates from L3JRC, a map recently generated from remote sensing of burn scars instead of active fires. Carbon fluxes were calculated by the novel fire model SPITFIRE embedded within the dynamic vegetation model framework LPJ-GUESS, using daily climate input. For the time period from 2001 to 2005 an average area of 195.5±24×104 km2 was burned annually, releasing an average of 723±70 Tg C to the atmosphere; these estimates for the biomass burned are within the range of previously published estimates. Despite the fact that the majority of wildfires are ignited by humans, strong relationships with climatic conditions have been identified in savannas worldwide, driving inter-annual variability. Our investigation of the relationships amongst carbon emissions and its potential drivers, available litter and precipitation showed that burned area as well as carbon emissions show a uni-modal response to precipitation with a maximum at ca. 1000 mm annual precipitation for burned area and emissions and a maximum of ca. 1200 mm annual precipitation for litter availability.