Recent evolution of spatial and temporal patterns of burnt areas and fire weather risk in the Iberian Peninsula

The weather is an important driver of the wildfire incidence because it strongly influences fuel availability and flammability. In the Mediterranean climate, the spatial and temporal patterns of fire weather present high variability, which help to understand the variable fire regimes. To assess this link in the Iberian Peninsula and the role of fire weather on fire incidence variability, this work identified pyro-regions, characterized the fire regimes in these regions and compared them with the spatial and seasonal distribution of several components of the Canadian Forest Fire Weather Index (FWI) System. A cluster analysis was performed on monthly normalized burnt area (NBA) series for the 1980 - 2015 period in each administrative division of the Iberian Peninsula (Portuguese districts and Spanish provinces), which revealed four pyro-regions (Northwest, North, Southwest and East) as well as significant spatial and temporal variability of NBA patterns. A separate analysis for 1980 - 1997 and 1998 - 2015 revealed noteworthy changes in the border of pyro-regions caused by changes in NBA seasonal patterns in some administrative regions. The analysis of the fire weather risk distribution for 1980 - 2017 included the assessment of extreme fire weather days, defined as days with Daily Severity Rating (DSR) above the 95th percentile, for the summer fire season, and as days with Drought Code above the 95th percentile, for the winter-spring fire season. The distribution of the monthly extreme fire weather days is highly correlated with the NBA seasonal variability and explains the differences between seasonal wildfire characteristics and the recent changes in the border administrative regions. The analysis of the fire weather patterns for large wildfires disclosed that these events were linked with extreme DSR days, especially in the NW pyro-region. These findings highlight the strong link between climate variability and fire regimes in the Iberian Peninsula, and can therefore help assess the impacts of climate change and to project future burnt area patterns.