Spatial variability in the relation between fire weather and burned area: patterns and drivers in Portugal

Abstract. Fire weather indices are used to assess the effect of weather conditions on wildfire behaviour and the high Daily Severity Rating percentile (DSRp) is strongly related to the total burned area (BA) in Portugal. The aims of this study were to: 1) assess if the 90th DSRp (DSR90p) threshold is adequate for Portugal; 2) identify and characterize regional variations of the DSRp threshold that justifies the bulk of BA; and, 3) analyse if vegetation cover can explain the DSRp spatial variability. We used wildfire data, weather reanalysis data from ERA5, for the 2001–2019 period, and the land use map for Portugal. DSRp were computed for an extended summer period and combined with individual large wildfires. Cluster analysis was performed using the relationship between DSRp and BA, in each municipality. Results revealed that the DSR90p is an adequate threshold for Portugal and well related to large BA. However, at the municipality scale, differences appear between the DSRp linked to the majority of accumulated BA. Cluster analysis revealed that municipalities where large wildfires occur in high DSRp present higher BA in forests and are located in coastal areas. In contrast, clusters with lower DSRp present greater BA in shrublands and are situated in eastern regions. These findings can support better prevention and fire suppression planning.