The occurrence, frequency and behaviour of wildland fires have varied greatly over time and space, chiefly as a result of the complicated influences of climate change and climate variability.
Also contributing to the variations have been changes in land use, vegetation composition, firefighting (meaning suppression) efforts, and other factors.
This complex combination of influences makes it difficult to identify clearly whether any measurable changes in the patterns of wildland fire over the last few decades can be linked directly to climate change. Nevertheless, pattern changes do appear to be underway.
In Canada’s northwestern boreal regions, for example, the annual amount of forest area burned by wildland fires rose steadily over the second half of the 20th century. Some of this increase has been attributed to climate change.
By contrast, in Canada’s southern boreal forest, the annual amount of area burned seems to have decreased during the 20th century. This trend might be the result of climate change causing greater amounts of precipitation over time in these regions.
However, analyses of fire history suggest that it is the effect of climate variability on precipitation regimes that is the primary reason for the decreasing fire activity in southern regions
“Climate change” vs “climate variability”
Climate change and climate variability share a common definition. Both refer to a change in the state of the climate—a change that is identifiable by shifts in the mean of climate properties (such as temperature and precipitation), and that persists for an extended period, typically decades or longer.
Generally speaking, however, the term “climate change” is most often used to mean human activity that alters the composition of the global atmosphere. And the term “climate variability” is used to mean changes that occur through natural processes over which humans have no control (for example changes in ocean currents or solar output).
Expected shifts in wildland fire patterns
Climate change during the 21st century is expected to result in more frequent fires in many boreal forests, with severe environmental and economic consequences.
From global climate models and scenarios, researchers are interpreting how climate change and climate variability may alter patterns of lightning, fuel moisture, temperature, precipitation and vegetation—all factors that can affect fire occurrence.
Fire-prone conditions are predicted to increase across Canada. This could potentially result in a doubling of the amount of area burned by the end of this century, compared with amounts burned in recent decades. Boreal forests, which have been greatly influenced by fire through history, will likely be especially affected by this change.
Other climate change impacts that could add damaged or dead wood to the forest fuel load (for example, as a result of insect outbreaks, ice storms or high winds) may increase the risk of fire activity.
New research is aimed at refining these climate change estimates of fire activity, and at investigating adaptation strategies and options to deal with future fire occurrence. There is growing consensus that as wildland fire activity increases, fire agency suppression efforts will be increasingly strained.