Recent trends in Central African fires and possible drivers

Fire is an integral Earth system process that links and influences regional and global biogeochemical cycles, human activity, and vegetation distribution and structure. Current estimates of global biomass burning suggest that Africa is responsible for ~70% of global burned area and ~50% of fire-related carbon emissions. Possible higher fire risks attributed to the warming climate and observed hydroclimatic variations over Central Africa raise the urgency to study potential variations in local fire events. Here we investigated long-term trends in fire using burned area data from the MODerate resolution Imaging Spectroradiometer (MODIS) and the Global Fire Emission Database (GFED4s) detections over Central Africa (10°E-40°E, 15°N-15°S) for the period 1997-2018. The 3-D connected component Labeling was applied to identify an individual fire and its size. We found that burned area has declined by 2.7-3.3 Mha (~1.3%) per year for the period 2003-2017, particularly in northern Central Africa. Decreased burned area was attributed to significant decrease in both fire frequency and size, particularly for large fire (> 100ha) which contributes to ~90% of the total burned area. The estimated decrease in burned area was the largest in savannas and grasslands, while burned area has increased at the edges of the Congolese rainforest. A random forest regression tree procedure was applied to address hypotheses concerned with anthropogenic and climatic influences as the drivers of burned area trends over different subregions. Overall, changes in burned area were less attributed to land use changes but were more affected by climatic variations such as annual rainfall, dry season length, specific humidity, wind and lightning. Decreased annual rainfall amount and longer dry season contributed to significant declined burned area over savannas and grasslands, where vegetation productivity and fuel availability were suppressed. Decreased lightning frequency during dry season was responsible for decreased burned area in savannas and grasslands south of the equator as well. Over edges of the Congolese rainforest, an intensifying dry season and decreased annual rainfall were responsible for more dehydrated vegetation (i.e., fuel) and increased burned area.