Ecoregion flammability thresholds: The global pyrogeography of dead fine fuel moisture content as a driver for wildfire activity

We identify the ecoregion flammability thresholds (EFTs) and the associated inflection point slope estimates (IPSEs) controlling landscapes' potential to burn for 791 distinct ecoregions. These thresholds were identified using a combination of: 1) the Terrestrial Ecosystems of the World regional classification system designating landscapes into hierarchical realms, biomes, and ecoregions; 2) ERA5 atmospheric reanalysis data to calculate dead fine fuel moisture content (DFFMC: %) using the Canadian Fire Weather Index (FWI) system; and 3) Moderate Resolution Imaging Spectroradiometer (MODIS) MCD64CMQ burnt area product. Nonlinear least squares regression formulae were fit to the association between an ecoregion's 25th percentile of DFFMC and the cumulative proportion of burnt area below a given value of DFFMC. Both the inflection point and reciprocal of the model scaling parameter were then extracted from the formulae and represent essential fuel moisture-fire threshold characteristics.