The effect of global warming on forest fires in Canada

The Canadian Fire Weather Index (CFWI) system is a wildfire risk evaluation tool used in several countries. This index estimates fire intensity based on meteorological variables. We use the CFWI framework to investigate how global warming will impact the risk of forest fires in Canada. We calculate the CFWI indices in equilibrium 5000-year integrations of the Canadian Earth system model (CanESM5) with different prescribed atmospheric CO₂ levels (pre-industrial to 4x pre-industrial). We find that higher atmospheric CO₂ levels lead to higher fire weather index (FWI) values and longer fire seasons across Canada. The yearly maximum FWI values also tend to increase with CO2, suggesting that global warming will raise the risk of extreme wildfire. The FWI  increase is mainly driven by temperature: higher CO₂ levels and temperatures lead to more efficient and sustained drying periods, resulting in more flammable, drier fuel for forest fires. However, more CO₂ in the atmosphere also leads to more precipitation, higher relative humidity, and slower wind speeds, resulting in regional differences in the response of CFWI to changes in CO₂. We further conduct a regional analysis of fire indices to examine how global warming will impact Canada at the provincial level. This model-based information will be useful to evaluate the risk of wildfire across Canada in the future, and a similar analysis could be applied in other world regions.