European fire weather synchronicity under climate change: three perspectives from regional to continental scales

European countries share essential firefighting equipment and personnel to manage wildfires. Nevertheless, climate change is increasing the likelihood of synchronous fire danger—periods when wildfire conducive weather conditions occur simultaneously across multiple European regions. Synchronous fire weather conditions could strain existing resource sharing plans and overwhelm firefighting capacities. To ensure an effective wildfire response in a warming climate, it is essential to understand how climate change influences the occurrence and spatial scale of synchronous fire danger.

 

Here, we analyze future fire weather synchronicity across ten European regions using the Canadian fire weather index (FWI) with three complementary perspectives—regional, inter-regional, and continental. Our analysis is based on a regional Single Model Initial condition Large Ensemble (SMILE), i.e. the CRCM5-LE, spanning the period from 1990 to 2099. This enables a robust quantification of both internal variability and forced response, as well as a sufficient sampling of extreme events. To identify impact-relevant fire weather conditions, we derive regional thresholds of FWI anomaly according to its cumulative distribution function (CDF) on burned area during 2001-2020, using CERRA reanalysis data and FireCCI burned area observations. Thereby, we focus on two levels of fire danger: moderate (FWI anomaly corresponding to 50% of burned area) and extreme (FWI anomaly corresponding to 90% of burned area). We then apply these regional thresholds to the FWI anomaly from the CRCM5-LE ensemble for each grid cell within the respective region. To quantify inter-regional and continental synchronicity, we compute weekly block maxima of the regional land area exceeding these thresholds as a proxy for regional fire danger.

 

From a regional perspective, we find that the magnitude (i.e., spatial extent) of fire danger increases with increasing global warming level (GWL) in all ten European regions. The increase is larger for extreme fire weather conditions than for moderate fire weather conditions. We find the strongest increases (fivefold) in the magnitude of extreme conditions in France and the Alps under 4 °C GWL. From an inter-regional perspective, we find an increasing pair-wise dependence of fire danger between regions under climate change, for both the moderate and extreme conditions. France, the Alps and Central Europe will become strongly dependent on each other in their weekly fire danger under 4 °C GWL. All region pairs show an emergence of synchronous fire danger between 2 and 3 °C GWL compared to 1990-2019, with southern regions emerging earlier (or at lower GWLs) than northern regions. From a continental perspective, we find that increasing GWLs also increases the odds of more than five European regions co-experiencing fire danger in one week, with an even stronger increase for extreme than moderate conditions.

 

Our results point toward increasing fire weather synchronicity in Europe under climate change and underscore the urgency to adapt current fire management strategies and collaboration in a warming climate. This is especially relevant for France, the Alps and Central Europe, that have historically low wildfire activity but will undergo a strong increase in fire danger under climate change.