Drivers of extreme burnt area in Portugal: fire weather and vegetation

Abstract

Abstract. Fire weather indices are used to assess the effect of weather on wildfire behaviour and to support fire management. Previous studies identified the high daily severity rating percentile (DSRp) as being strongly related to the total burnt area (BA) in Portugal, but it is still poorly understood how this knowledge can support fire management at a smaller spatial scale. The aims of this study were to (1) assess whether the 90th DSRp (DSR90p) threshold is adequate for estimating most of the BA in mainland Portugal; (2) analyse the spatial variability of the DSRp threshold that explains a large part of BA, at higher resolution; and, (3) analyse whether vegetation cover can justify the DSRp spatial variability. We used weather reanalysis data from ERA5-Land, wildfire and land use data from Portuguese land management departments for an extended summer period (15 May to 31 October) from 2001 to 2019. We computed and related DSRp to large wildfires (BA > 100 ha) and land use to clarify the effectiveness of the DSRp for estimating BA in Portugal and assess how vegetation influences it. Results revealed that the DSR90p is an adequate indicator of extreme fire weather days and BA in Portugal. In addition, the spatial pattern of the DSRp associated with most of the total BA shows variability at the municipality scale. Municipalities where large wildfires occur with more extreme weather conditions have most of the BAs in forests and are in coastal areas. By contrast, municipalities where large wildfires occur with less extreme weather conditions are predominantly covered by shrublands and are situated in eastern and inland regions. These findings are a novelty for fire science in Portugal and should be considered by fire managers and fire risk assessors.

The Influence of Wildfire Climate on Wildfire Incidence: The Case of Portugal

“…A concentration of the incidence of wildfires, not just the larger ones, in certain regions is evident, as has already been reported in previous studies [12,15,16,61,70,[92][93][94][95][96]. This spatial heterogeneity is necessarily associated with climatic (spatial) variability, namely with the fact that the atmospheric conditions conducive to the occurrence and development of wildfires do not have to be observed simultaneously throughout the territory, at least with the same magnitude, despite the small size of the country [57,[97][98][99].…”

“…Several previous studies point to the influence of wildfire climate on wildfire incidence in Portugal and the world, especially on the spatial and temporal distribution, especially in the intraannual variability [25,31,[51][52][53][54]. In Portugal and many regions of the world, the interannual variability of wildfire incidence is essentially due to climatic variability and the occurrence of anomalous wildfire weather and extreme events [15][16][17][18]34,39,[55][56][57][58][59][60]. However, the objective and quantitative assessment of this influence in all its dimensions is a gap in the current state of knowledge of wildfire science.…”