Fire regime

Fire regime describes the pattern (type, frequency, intensity, size, seasonality, severity, cause of ignition) of wildland fire in a particular area or ecosystem over time. It is influenced by:

• fuel
• climate
• ignition source
• topography
• land use
• fire suppression activities

View monthly and seasonal forecast maps on the Canadian Wildland Fire Information System (CWFIS).

Understanding fire regime is important for:

• assessing the likelihood of wildland fire and its possible impacts
• developing effective suppression strategies
• recognizing biophysical processes that vary over time and space
• managing forest resources
• adapting to climate change

Changes in fire regime can significantly affect:

• infrastructure and property
• health and safety
• availability and accessibility of resources
• forest health and vegetation type
• Canada’s carbon flux

Wildland fire activity in Canada naturally varies from year to year, but the hotter and drier conditions caused by climate change are shifting fire patterns and dynamics beyond historical observations. Projections indicate that by 2100, some regions may face fire seasons lasting over a month longer, resulting in an increase in the amount of forest area burned annually.

Fire regime components

Wildland fire has a crucial role in forest regeneration and maintaining healthy and diverse ecosystems. Fire regimes vary widely across Canada and are characterized by a set of fire-related metrics that capture fire activity patterns across space and time. These metrics include:

• Ignition (natural or human activity)
  • wildland fires can be ignited by lightning or by human activities (campfires, road traffic, powerlines, etc.)
  • fire occurrences (frequency, location, season) tend to differ depending on the ignition cause
• Frequency (temporal dynamic)
  • represents the number of fires per year within a region
  • can also describe the average number of years between 2 fire events (fire interval)
• Fire size (spatial extent)
  • represents the area burned by a fire, usually in hectares (ha)
  • provides insights about the area impacted, as well as the spatial distribution of burn scars across the landscape
  • although most wildland fires in Canada's managed forests are contained or self-extinguished before reaching 200 ha in size, fires that grow beyond this threshold make up approximately 97% of the area burned annually
• Fire intensity and severity (fire behaviour)
  • fire intensity represents the energy released from the fire or characterizes fire behaviour (i.e., flame length, rate of spread)
  • fire severity describes the consumption or alteration in organic matter above and belowground
  • fire behaviour affects air quality, vegetation, soils, as well as other ecosystem components, and it informs fire suppression strategies
• Seasonality (time of year)
  • seasonal changes influence fuel and weather conditions, which in turn affect fire size, frequency and behaviour
  • determines leaf flush of broadleaf trees, which influences fire behaviour and occurrence
• Fire type
  • ground fire: smolders beneath the forest floor in organic material, burning at varying depths based on organic matter and drought conditions
  • surface fire: burns through ground-level materials like dead leaves and vegetation without reaching the tree crowns; occasional flare-ups (torching) may occur and embers can be carried by wind to create new fires (spotting)
  • crown fire: advances through the treetops (canopy) usually alongside a surface fire, creating a wall of flame that spreads rapidly and poses significant challenges for fire suppression

These fire regime metrics can be combined to obtain statistics such as annual area burned (AAB), average surface area burned annually or fire cycle (number of years needed to burn the equivalent of a given area).

Fire Regime Units and Fire Regime Types

A fire regime zonation system divides landscapes into distinct geographical areas that share similar fire behaviours and environmental characteristics. This approach helps understand fire patterns across large regions by breaking complex landscapes into simpler, homogenous zones. At the Canada-wide scale, two main systems are currently used:

• Fire Regime Units (FRUs)
  • 60 geographical areas across Canada
  • fire characteristics (i.e., frequency, size, burn rate, seasonality, ignition cause) tend to be relatively similar within a specific FRU
  • detailed, local level
• Fire Regime Types (FRTs)
  • 15 classifications across Canada
  • characterized by a unique set of indices related to fire activity, seasonality and ignition cause
  • broader, regional or national scale

Fire regime zonation systems are important for:

• understanding fire dynamics at large spatial scales
• identifying knowledge gaps about fire activity across time and space
• reducing uncertainty in anticipating how fires interact with their environment
• serving as a baseline for measuring changes driven by climate and human activities
• developing region-specific strategies for
  • wildland fire management (mitigation and suppression)
  • community protection and well-being
  • biodiversity, and forest productivity
• ensuring wildland fire management practices support the health, recovery and resiliency of impacted ecosystems

Fire regime and climate change

Changes in fire regime resulting from climate change can have significant impacts to Canada’s forests, our forest industry and ourselves. The annual area of burned forest and the number of large fires (>200 ha) have increased since 1959, when comprehensive monitoring of wildland fire in Canada began. Projections indicate continued increases to both in the future.