CLIMATE AND WILDFIRES IN
BRITISH COLUMBIA
In recent years, especially during the record-breaking 2023 wildfire season, wildfires have increased in area not only in BC, but across the whole country of Canada.
Climate parameters such as temperature and precipitation, but also wind and relative humidity play a major role in terms of wildfire risk (Pagnon et al. 2023).
Since Canada is a country that is highly influenced by climate change and it is the climate parameters that determine the wildfire risk, it is necessary to investigate whether climate change is responsible for the increasing wildfire risk observed in Canada. The following analysis contributes to this by examining the correlation between the area burned by wildfires per year and the two climate parameters temperature and precipitation. Correlations with the annual mean temperature and the total annual precipitation were determined for both the annual wildfire data and the 5-year mean values of the burned area.
This was done for 3 selected regional districts of British Columbia in the period from 1951 to 2020. The selection of the investigated regions was based on trends in burned area during the study period as well as the burned area relative to the total area of the district. The regional districts of Cariboo and Bulkley-Nechako were chosen because their burned area has increased more strongly compared to any other regional district over the 70-year study period. The Kootenay Boundary regional district was selected because a larger area burned down than in any other regional district compared to the total area of the respective regional district. The location of the districts studied within British Columbia is shown on the map to the right.
For more information on the data and the statistical methods used, see the Statistical Analysis section in Methods.
Temperature, precipitation and wildfires in Cariboo
Temperature, precipitation and wildfires in Bulkley-Nechako
The regional district of Bulkley-Nechako has a total area of 73,361 km². Similar to the observations from Cariboo, high values of the burnt area in Bulkley-Nechako only occurred after the year 2000, while the mean annual temperature started to increase since the 1990s and precipitation only showed a slight increase. The largest area (556,728 ha) burned down during the 2018 wildfire season.
The results of the correlations also show very comparable results to those in Cariboo. The only significant correlation was found for the mean annual temperature and the 5-year mean of the burned area (p < 0.05; ρ = 0.29).
Cariboo has a total area of 80,609 km². In no other regional district in British Columbia, the area burned by wildfires has increased as strongly as in Cariboo over the last 70 years. The burned area was generally low over large parts of the study period until it started to increase since the year 2002, reaching its peak in 2017 (1,068,999 ha). The mean annual temperature showed an increase since the 1990s while annual precipitation remains relatively stable.
The table to the right shows the p-values and the correlation coefficient ρ (rho) for the correlations between temperature and burned area (annual values and 5-year mean) and precipitation and burned area (annual values and 5-year mean). All correlations (not only in Cariboo, but also in Bulkley-Nechako and Kootenay-Boundary) between a climate parameter and the annual values of the burned area were strongly insignificant (p-values ≥ 0.46). While no significant correlation could be found for precipitation and the 5-year means of the burned area, a moderate significant correlation (p < 0.05; ρ = 0.31) was identified for temperature and the 5-year means of the burned area.
With a total area of 8,084 km², Kootenay-Boundary is the smallest of the three regions studied. Of all the regional districts, the area burned by wildfires is the largest compared to the area of the district in Kootenay-Boundary. Even though the figure shows that extreme fire seasons occured more frequently after the year 2000 than before, there were also years in the 1950s, 1970s and 1980s in which large areas in Kootenay-Boundary burned down. While no clear trend in total annual precipitation was found, the mean annual temperature has been increasing since the 1990s.
As presented in the table to the right, none of the correlations between temperature or precipitation and burned area was significant. The lack of correlation between the temperature and the 5-year mean of the burned area can be explained by the extreme fire seasons that have already occurred in the last century.
Temperature, precipitation and wildfires in Kootenay-Boundary
Conclusion
Nevertheless, such an influence could still be present, which is why more detailed analyses need to be carried out to get to the bottom of the connection. It is particularly important to analyse small-scale temporal patterns in temperature and precipitation, which can lead to high wildfire risk during the fire season.
The analyses show that severe wildfire seasons in Cariboo and Bulkley-Nechako rarely occurred before the year 2000, while this is not the case for Kootenay Boundary. Significant correlations were only identified between temperature and the five-year mean of the burned area in Cariboo and Bulkley-Nechako in the period from 1951 to 2020. In this form, the results do not indicate a strong influence of climate change on wildfires.