Spatio-temporal trends in fire weather in the French Alps

Abstract

The Alpine area is particularly sensitive to climatic and environmental changes that might impact socio-ecosystems and modify the regime of natural hazards. Among them, wildfire is of major importance as it threatens both ecosystems and human lives and infrastructures. Wildfires result from complex interactions between available vegetation fuels, climate and weather, and humans who decide of the land use and are the main source of fire ignitions. The changes in fire weather during the past decades are rather unknown in the French Alps especially due to their complex topography. Moreover, local institutions and managers wonder if the ongoing climate changes might increase fire risk and affect the environmental quality and the different ecosystem services provided by the mountain forests. In this context, we used the national forest fires database together with daily meteorological observations from 1959 to 2015 to investigate the changes in wildfire danger in the French Alps. We analysed the spatial and temporal variations in terms of intensity, frequency, seasonality and window of opportunity of two fire weather indices: the fine fuel moisture code (FFMC) and the fire weather index (FWI) that measure the daily water content of vegetation and the potential intensity of fires, respectively. Our results showed a major contrast between Southern Alps with a high fire weather danger on average and a significant increase in the past decades, and Northern Alps with low to moderate danger on average that increased only at low elevations. This study contributes to the understanding of the consequences of ongoings climate changes on wildfires in the French Alps. It produced high resolution results that account for the topographic and climatic variability of the area. Finally, the maps of the different fire weather components have practical implications for fire management and modelling and for preventing indirect effects of fires on ecosystems and human assets.

Aridity and competition drive fire resistance trait covariation in mountain trees

“…The increasing severity of fire weather conditions (Dupire et al. ) together with higher fire intensity and crown fire likelihood at the dry range margin of mountain trees (Fréjaville et al. ) may increase the importance of fire resistance traits driving the composition of mountain forests, and the response of their communities to climate change.…”

“…Our results thus emphasize the importance of individual variability in understanding community assembly processes (Laughlin et al 2012) that may be critical for predicting how changing fire regimes (Fr ejaville and Curt 2017) will shift the distributions of fire-sensitive and fire-resistant mountain tree species. The increasing severity of fire weather conditions (Dupire et al 2017) together with higher fire intensity and crown fire likelihood at the dry range margin of mountain trees (Fr ejaville et al 2018) may increase the importance of fire resistance traits driving the composition of mountain forests, and the response of their communities to climate change.…”

“…), and fires are expected to increase in frequency and intensity with future warmer and drier conditions (Schumacher and Bugmann , Dupire et al. ). Paleoecological analyses have shown long‐term differences in fire activity between species and plant communities in the Alps (Tinner et al.…”

Has fire policy decreased the return period of the largest wildfire events in France? A Bayesian assessment based on extreme value theory

“…In mid-elevation hinterland (PCr-2) and in mountains (PCr-3), only a dozen fires larger than 100 ha were recorded each year on average since the 1990s. The ongoing climate changes favor an extension of areas with high fire weather danger towards the north and in the mountains (Dupire et al, 2017), and the season favorable to fire activity becomes longer. However, ignitions remain limited and fuels are rarely fully dry.…”

Ecohydrological dynamics in the Alps: Insights from a modelling analysis of the spatial variability

“…The European Alps—situated in the transition between the Mediterranean Sea and the Atlantic Ocean—comprise a unique mosaic of microclimates and vegetation types, which renders this area particularly interesting, but also complicates modelling attempts (Beniston, ). In the European Alps, air temperature is rising faster than the global average (Brunetti et al, ), reducing snow cover duration (Beniston et al, ) and increasing drought occurrence (Timofeeva et al, ), tree mortality (Rebetez & Dobbertin, ), and wildfires (Dupire, Curt, & Bigot, ). Observations show that vegetation species composition is changing in certain areas (Rigling et al, ); these changes might accelerate in the future (Booth et al, ; Schumacher & Bugmann, ).…”