# Fire Activity and Fuel Consumption Dynamics in Sub-Saharan Africa
## 4 Results
### MOD17 Productivity Assessment  
Prior to their use in fuel load estimation, an assessment of the MODIS productivity estimates (which include both growth and maintenance respiration terms) was carried out using the Copernicus dry matter productivity (DMP) product of reference [64] which is driven by Proba-V data and available from the Copernicus Global Land Service at 10-day temporal resolution and 1 km spatial resolution. Using three years of data (2013-2016), the productivity estimates were integrated over the MODIS burned areas (e.g., 'fire clusters') which burned in successive years, as described in Section 3. The results shown in Figure 3 indicate a stronger relationship between both datasets in southern hemisphere Africa (\(r=0.96\)) than in the northern hemisphere (\(r=0.8\)). A difference in magnitude is also evident between the MODIS and Copernicus products, with the former lower (albeit the latter does not account for below ground biomass or the costs associated with growth and maintenance respiration in woody tissue). To assess the impact of these respiration terms, the average ratio between annual MODIS NPP and annually accumulated MODIS PSN was calculated and reveals that, over Africa, 88% of pixels have a NPP/PSN ratio between 0.7-0.8 and that 40% of the pixels have a value of 0.79. The annual NPP/PSN ratio is more variable in northern hemisphere Africa where lower ratios occur in the tropical forests of central and west Africa (0.68-0.75) and the parts of Sahel and CAR (<0.65). The basis for comparing FRE-derived fuel consumption estimates to MODIS PSN estimates, which includes maintenance respiration and growth respiration of woody material, rather than the Copernicus DMP estimates is that these data only cover 2013-present whilst a longer time-series is available from MODIS. Comparison between FRE-Derived Fuel Consumption and MODIS Accumulated PSN and Copernicus Dry Matter Productivity (DMP)  
Here we provide the first comprehensive assessment of the relationship between FRE-derived fuel consumption (Tg DM) and temporally integrated MODIS PSN productivity (Tg) and Copernicus DMP (Tg DM) estimates. MODIS PSN estimates (2004-2016) are used as a surrogate for NPP since the latter is only available on an annual basis, which is inconsistent with the seasonal dynamics of landscape fires. It is acknowledged that FRE-derived fuel consumption is not directly comparable to PSN, since the latter contains contributions from woody material maintenance, growth respiration and below  
Figure 3: Comparison between MODIS net photosynthesis (PSN) (Tg) and Copernicus dry matter productivity (DMP, Tg DM) estimates that have been temporally integrated over MODIS burned areas that burned in successive years in the northern (**a**) and southern (**b**) African hemispheres. The grey shaded area represents the prediction interval and the blue shaded area is the slopes 95% confidence interval. Note that the \(x\)- and \(y\)-axis range differs among plots. ground biomass. Therefore, irrespective of variations in the combustion completeness, the temporally integrated PSN value should be greater than the FRE-derived fuel consumption estimates. The focus was on areas whose burning encompassed twenty or more MCD64A1 MODIS 500 m burned area pixels, thus omitting the smaller fires which SEVIRI finds harder to identify [41; 65]. The accumulated productivity estimates between the two years of burning were remapped into SEVIRI's grid and the total available fuel per burned area 'fire cluster', or contiguous cluster of pixels, calculated using the burned area (m\({}^{2}\)) measurements (assuming 47% fuel carbon content; reference [66]).