Linking fire synchronicity in Europe to persistent weather regimes

Synchronous fires, that is fires co-occurring at different geographical locations within a few days of each other, challenge the distribution of firefighting resources among regions and can have more severe impacts on human health, infrastructure and environmental systems than individual fire events. However, so far very little is known about the occurrence, spatial patterns and the atmospheric drivers of synchronous fires in Europe.

In this work, we use fire observations from a global fire event dataset FRYv2.0 to (1) detect fire synchronicity between ten European regions during 2001–2020 and (2) link the occurrence of synchronous fires to seven dominant European-Atlantic weather regimes. To detect fire synchronicity, we apply complex network theory and an event synchronicity statistical framework to identify significant links between the ten regions. To analyze the relationship between synchronous fire events and dominant weather regimes, we use a conditional probability-based measure calculating the dependency of synchronous fires –between each region pair– on seven common European weather regimes. We perform 2000 block permutations to test the statistical significance of these dependencies. Lastly, we use the CERRA reanalysis data to analyze the seasonal anomalies of relevant atmospheric variables under each weather regime, including temperature, wind speed, precipitation and relative humidity.

We find multiple significant connections between regions across Europe showing fire synchronicity in spring, summer and fall. We show that (1) northern and western regions in Europe experience fire synchronicity in spring under the influence of blocking regimes (i.e., European and Scandinavian Blocking) which promote warm and dry conditions; (2) eastern regions show fire synchronicity in spring and fall during the Zonal Regime under warm and dry conditions; and (3) fire synchronicity in southern regions are significantly modulated by Scandinavian Troughs due to positive wind speed anomalies and dry conditions in spring and fall as well as by Atlantic Ridges due to positive wind speed anomalies in summer.

Our work reveals significant fire synchronicity across Europe with significant links to atmospheric circulation patterns. As the seven weather regimes have predictability on weekly to monthly time scales, our work might help to develop early warning systems for elevated risks of synchronous fires under climate change and improve fire emergency preparedness across different European regions.