Environmental factors affecting wildfire-burned areas in southeastern France, 1970–2019

Résumé En

Forest fires burn an average of about 440 000 ha each year in southern Europe. These fires cause numerous casualties and deaths and destroy houses and other infrastructure. In order to elaborate on suitable firefighting strategies, complex interactions between human and environmental factors must be taken into account. In this study, we investigated the spatiotemporal evolution in the burned area over a 50-year period (1970–2019) and its interactions with topography (slope aspect and inclination) and vegetation type in southeastern France by exploiting the geographic information system (GIS) databases. Data were analyzed for two 25-year periods (1970–1994 and 1995–2019), since a new fire suppression policy was put into place after 1994, which focused on rapid extinction of fires in their early phase. In the last 25 years, the burned area decreased sharply, and the geographic distribution of fires also changed, especially in regions where large fires occur (Var administrative division). Elsewhere, even though forest fires remain frequent, the total extent of the burned area decreased substantially. Fire hotspots appear closer to built-up areas in the west, are randomly distributed in the east, and they almost completely disappear in the central region of the study area where there is a history of large fires. Slope orientation presents an increasingly important role in the second period; south-facing slopes are preferred the most by fire, and north-facing slopes are preferentially avoided. Even though the slope inclination is less affected by the new firefighting strategy, low slope inclinations are even more avoided after 1994. The greatest proportion of the burned area is strongly associated with the location of sclerophyllous vegetation clusters which exhibit highly fire prone and expand in area over time. Natural grasslands are also preferred by fire, while broadleaved, coniferous, and mixed forest are increasingly avoided by fire.