Abstract
African landscape fires are widespread, recurrent and temporally dynamic. They burn large areas of the continent, modifying land surface properties and significantly affect the atmosphere. Satellite Earth Observation (EO) data play a pivotal role in capturing the spatial and temporal variability of African biomass burning, and provide the key data required to develop fire emissions inventories. Active fire observations of fire radiative power (FRP, MW) have been shown to be linearly related to rates of biomass combustion (kg s−1). The Meteosat FRP-PIXEL product, delivered in near real-time by the EUMETSAT Land Surface Analysis Satellite Applications Facility (LSA SAF), maps FRP at 3 km resolution and 15-min intervals and these data extend back to 2004. Here we use this information to assess spatio-temporal variations in fire activity across sub-Saharan Africa, and identify an overall trend of decreasing annual fire activity and fuel consumption, agreeing with the widely-used Global Fire Emissions Database (GFEDv4) based on burned area measures. We provide the first comprehensive assessment of relationships between per-fire FRE-derived fuel consumption (Tg dry matter, DM) and temporally integrated Moderate Resolution Imaging Spectroradiometer (MODIS) net photosynthesis (PSN) (Tg, which can be converted into pre-fire fuel load estimates). We find very strong linear relationships over southern hemisphere Africa (mean r = 0.96) that are partly biome dependent, though the FRE-derived fuel consumptions are far lower than those derived from the accumulated PSN, with mean fuel consumptions per unit area calculated as 0.14 kg DM m−2. In the northern hemisphere, FRE-derived fuel consumption is also far lower and characterized by a weaker linear relationship (mean r = 0.76). Differences in the parameterization of the biome look up table (BLUT) used by the MOD17 product over Northern Africa may be responsible but further research is required to reconcile these differences. The strong relationship between fire FRE and pre-fire fuel load in southern hemisphere Africa is encouraging and highlights the value of geostationary FRP retrievals in providing a metric that relates very well to fuel consumption and fire emission variations. The fact that the estimated fuel consumed is only a small fraction of the fuel available suggests underestimation of FRE by Spinning Enhanced Visible and Infrared Imager (SEVIRI) and/or that the FRE-to-fuel consumption conversion factor of 0.37 MJ kg−1 needs to be adjusted for application to SEVIRI. Future geostationary imaging sensors, such as on the forthcoming Meteosat Third Generation (MTG), will reduce the impact of this underestimation through its ability to detect even smaller and shorter-lived fires than can the current second generation Meteosat.
Highlights
Andela and van der Werf [16] indicates that over roughly the last decade, annual burned area in southern hemisphere Africa has been on a generally slightly upward trajectory whilst a decreasing trend is observed in northern hemisphere Africa which is attributed to the expansion of cropland into savanna
This study has used a variety of remotely sensed datasets to investigate the spatial and temporal variations in fire activity and fuel consumption across sub-Saharan Africa, focusing on years between 2004 and 2016
The agreement in the southern hemisphere (r >= 0.9) is stronger than that found in the northern hemisphere (r > 0.66) and is consistent on an annual basis, but it is clear that the fire radiative energy (FRE)-derived fuel consumptions are underestimated
Summary
Data from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra and Aqua polar orbiting satellites is used to provide burned area products [9,10,11,12]. These data feed into so-called ‘bottom-up’ fire emissions inventories, such as the widely-used Global Fire Emissions Database (GFED; [13,14]). Andela and van der Werf [16] indicates that over roughly the last decade, annual burned area in southern hemisphere Africa has been on a generally slightly upward trajectory (possibly driven by climate anomalies occurring over this period) whilst a decreasing trend is observed in northern hemisphere Africa which is attributed to the expansion of cropland into savanna
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