Impacts of climate variability and change on regional fire weather in heterogeneous landscapes of Central Europe

Wildfires have reached an unprecedented scale in recent fire seasons of the Northern Hemisphere as demonstrated by the summers of 2021 and 2022. Severe fire seasons, characterized by heat, drought and windy conditions, might become even more frequent and will extend to more temperate regions in northern latitudes under global warming. Still, quantifying the effects of climate change on future fire danger is challenging because natural variability hides trends of increasing fire danger in climate model simulations in future potentially fire-prone areas. Single Model Initial-Condition Large Ensembles (SMILEs) help scientists to distinguish climate trends from natural variability. Here, we leverage the capabilities of SMILEs to assess future changes in fire weather conditions in a currently non-fire-prone area in Central Europe. The study area covers four heterogeneous landscapes, namely the Alps, the Alpine Foreland (southern parts), the lowlands of the Southern German Escarpment, and the eastern mountain ranges of the Bavarian Forest (northern parts). We use a SMILE of the Canadian regional climate model version 5 (CRCM5-LE) under the RCP 8.5 scenario from 1980 to 2099 to analyze trends in fire danger quantified by the globally applicable Canadian Fire Weather Index (FWI).

Our results show the strongest increases for the median (50th percentile) and extreme (90th percentile) FWI in the northern parts of the study area during the late summer months July, August and September. The southern, more alpine parts are affected less strongly and show high fire danger mostly in August by the end of the 21st century for the median FWI. Over the whole study area, we find that the extreme FWI in the present climate period will become much more frequent at the end of the century. In the South German Escarpment and Eastern Mountain Ranges, the climate change trend exceeds natural variability in the late 2040’s. Due to weaker variability, the time of emergence is reached in the Alps and Alpine Foreland in the early 2040's.

These results demonstrate that the CRCM5-LE is a suitable dataset to disentangle climate trends from natural variability in a multivariate fire danger metric. Our study emphasizes that regions with a low fire danger under current climate conditions will experience weather conditions facilitating the development of potentially uncontrollable wildfires in a warming climate.