Global Fire Emissions Database version 4 (GFED4)

We present the fourth generation of our Global Fire Emissions Database (GFED4). Burned area was derived from satellite-based 500-meter maps (MODIS MCD64A1 burned area product) for the MODIS era and relations with active fire detections from the VIRS and ATSR sensors for the pre-MODIS era as described in the GFED4 burned area dataset. In addition, we added new estimates of contributions in burned area from relatively small fires that were detected by active fire algorithms but not the MCD64A1 product. Modeled fuel consumption was optimized in the modeling framework by adjusting turnover rates and compared reasonably well with measurements at the biome-level. However, discrepancies are still substantial in some biomes, highlighting the difficulty in representing fuel dynamics. For the boreal biome, we used new satellite-derived information to inform combustion completeness and fire-induced tree mortality. In general, fuel consumption (kg C m-2 of burned area) decreased compared to GFED3, especially in regions dominated by herbaceous fuels. This is compensated for by the higher burned area estimates due to the addition of small fire burned area. However, these small fires are difficult to validate at large scales, which adds to our uncertainty. In regions where small fires may play a large role, including the US, Central America, Europe, and parts of Southeast Asia, emissions have increased substantially and are now sometimes twice as high as GFED3 estimates. Global mean annual emissions over 1997-2013 were 2.1 Pg C, 350 Tg CO, and 16 Tg CH4; in general somewhat higher than GFED3 because increases in burned area were larger than decreases in fuel consumption. Interannual variability was especially large in the first years of our record with high emissions in 1997 and 1998 (3.0 and 2.7 Pg C, respectively), while the lowest year in our record was 2000 (1.8 Pg C). Emissions were also relatively low during the latter part of the record with decreasing emissions from fires associated with tropical deforestation and with socio-economic developments in northern hemisphere Africa. Interannual variability was still substantial after 2000 in many regions, especially those with high forest cover, but these regions tended to cancel each other out on a global scale; emissions remained between 1.8 and 2.3 Pg C per year after 2000.