Fire weather

Increases in length of fire season will affect forest ecosystems and human health and safety.

Fire weather refers to weather conditions that are conducive to wildland fire, affecting their occurrence and subsequent behaviour. It determines the fire season – the period each year in which forest fires are likely to start, spread and do damage. Changes in fire weather affect forest ecosystems, as well as human health and safety and the ability to access the forest.

Preliminary analyses show that the fire season has become longer in some regions of eastern Canada and shorter in most of southwestern Canada. Future projections suggest that the fire season will lengthen in almost all areas. By 2100, the fire season in certain forest regions may have lengthened by more than a month.

Read how fire weather and its indicators are defined

Fire weather refers to weather conditions that are conducive to fire. These conditions determine the fire season, which is the period(s) of the year during which fires are likely to start, spread and do sufficient damage to warrant organized fire suppression. By contrast, fire seasonality refers to the moment when fires actually occur.

Forest Change fire weather indicators include the start, end and length of fire season. They are very sensitive to climate change and are highly associated with fire risk. The start- and end-of-fire-season indicators were estimated using the Forest Fire Weather Index (FWI) start-up and end dates.

  • Start of fire season – For stations that report significant snow cover during the winter (i.e., more than 10 cm, with snow cover present at least 75% of the days in January and February), start-up occurs when the station has been snow-free for 3 consecutive days, with noon temperatures of at least 12°C. For stations that do not report significant snow cover during the winter, start-up occurs when the mean daily temperature has been 6°C or higher for 3 consecutive days (6°C represents the approximate lower limit for plant growth).
  • End of fire season – The fire season ends with the onset of winter, generally following 7 consecutive days of snow cover. If there are no snow data, shutdown occurs following 7 consecutive days with noon temperatures lower than or equal to 5°C.
  • Length of fire season – The start- and end-of-fire-season dates determine the total length of the fire season.

Why fire weather is important

Forest ecosystems and human health and safety, as well as timber supply face fire risks during the fire season.

Wildland fires are natural disturbances that occur in forest ecosystems. They affect human health, through smoke emissions and safety risks, and reduce the ability to access the forest for both recreation and economic activities. Wildland fires also can affect vast amounts of timber supply.

Understanding changes in fire weather over time can allow for better management of forest resources by taking into account spatiotemporal changes in fire risk. It can also allow forest communities to better plan for wildland fire evacuations.

What has changed?

The length of fire season has increased in some regions of eastern Canada and has become shorter in most of southwestern Canada.

Preliminary analyses show that the length of fire season has increased in some regions of eastern Canada and decreased in most of southwestern Canada. New analyses and maps are being done to identify whether changes were predominantly a result of an earlier start or a later ending of the fire season.

 

The outlook

Fire season is expected to become longer in almost all areas.

The projected increase in spring and fall temperatures will have a strong influence on fire season start date (Figure 1), end date (Figure 2) and length (Figure 3), particularly in areas subject to reductions in winter precipitation and earlier snowmelt.

Mainly as a result of projected earlier start dates, the length of the fire season (Figure 3) is expected to increase in almost all areas, by 2100 becoming longer by more than a month in certain regions (e.g., central and eastern Quebec, and northern British Columbia). Even areas that showed a recent shortening of the fire season length, such as southern coastal British Columbia, are projected to have a longer fire season (Figure 3).

Set of five maps of Canada showing the mean start date of the fire season for the reference period 1981–2010 compared to the projected start dates for the short term (2011–2040), medium term (2041–2070), and long term (2071–2100) using climate scenario RCP 2.6 and again, for the long term, using climate scenario RCP 8.5.

Figure 1 – Reference period (1981–2010) and projected fire season start dates for the short- (2011–2040), medium- (2041-2070), and long-term (2071–2100) under the Representative Concentration Pathway (RCP)Footnote * 2.6 (rapid emissions reductions) and, for the long-term (2071–2100), under RCP 8.5 (continued emissions increases) for Canada

Larger image [301 Kb]

Set of five maps of Canada showing the mean end date of the fire season for the reference period 1981–2010 compared to the projected end dates for the short term (2011–2040), medium term (2041–2070), and long term (2071–2100) using climate scenario RCP 2.6 and again, for the long term, using climate scenario RCP 8.5.

Figure 2 – Reference period (1981–2010) and projected fire season end dates for the short- (2011–2040), medium- (2041-2070), and long-term (2071–2100) under the Representative Concentration Pathway (RCP)Footnote * 2.6 (rapid emissions reductions) and, for the long-term (2071–2100), under RCP 8.5 (continued emissions increases) for Canada

Larger image [369 Kb]

Set of five maps of Canada showing the mean length of the fire season for the reference period 1981–2010 compared to the projected length of the fire season for the short term (2011–2040), medium term (2041–2070), and long term (2071–2100) using climate scenario RCP 2.6 and again, for the long term, using climate scenario RCP 8.5.

Figure 3 – Reference period (1981–2010) and projected fire season length for the short- (2011–2040), medium- (2041-2070), and long-term (2071–2100) under the Representative Concentration Pathway (RCP)Footnote * 2.6 (rapid emissions reductions) and, for the long-term (2071–2100), under RCP 8.5 (continued emissions increases) for Canada

Larger image [303 Kb]

 
Sources and references for fire weather and its indicators

Canadian Forest Service key contacts

Richard Carr, Fire Research Analyst, Northern Forestry Centre
Yan Boulanger, Research Scientist, Forest Ecology, Laurentian Forestry Centre

Adaptation tools and resources

Fire Smart Canada – helps people understand the potential of wildland fire affecting homes and communities; includes a risk reduction program for forestry companies

Forest Change Toolkit – a list of tools and resources for climate change adaptation

Find out more
Related Canadian Forest Service research