How Has the Southern African Biomass Burning Season Changed in the Last 20 Years?

Biomass burning over Africa accounts for roughly half of global, fire-related carbon emissions. Fire risks are projected to increase as temperatures rise with climate change, but because the number of fires is mostly declining currently in southern Africa, the future impacts of African fires and their aerosol emissions are uncertain. Here we examine the processes that govern smoke and fire variability on multi-year time scales during June-November, using primarily the MODIS burned-area data processed at 250m spatial resolution by the ESA’s Fire_cci project (FireCCI51, 2001-2020), combined with a 40-year ERA5 data record and a 17-year carbon monoxide (CO) time series from an ECMWF aerosol reanalysis (EAC4). Leading questions are understanding changes to the seasonal evolution of wildfires over time, how climatic trends in tropical and subtropical circulations affect seasonal meteorology, and how the circulation changes impact the smoke transport over time. While CO has decreased globally with reductions in industrial emissions, it has slightly increased in the lower free troposphere over the southeast Atlantic, despite reduced fires in the savannas and grasslands of southern Africa. Further south, increased land surface temperatures have contributed to increased and expanded southern African easterly jet wind speeds during the austral winter and spring, enabling the increased CO levels over the southeast Atlantic.