Increases in length of fire season will affect forest ecosystems and both human health and safety.
Fire weather refers to weather conditions that are conducive to wildland fire, affecting its occurrence and subsequent behaviour. It determines the fire season – the annual period during which forest fires are likely to start, spread, and cause 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.
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 can also 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.
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).
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 annual period(s) of the year during which fires are likely to start, spread, and cause sufficient damage to warrant organized fire suppression. By contrast, fire seasonality refers to the moment when fires actually occur.
The 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.
Sources and references for fire weather and its indicators
- Albert-Green, A., Dean, C.B., et al. 2012. A methodology for investigating trends in changes in the timing of the fire season with applications to lightning-caused forest fires in Alberta and Ontario, Canada. Canadian Journal of Forest Research 43, 39–45.
- Canadian Interagency Forest Fire Centre (CIFFC). 2003. Glossary of forest fire management terms [374 Kb PDF].
- Intergovernmental Panel on Climate Change (IPCC). 2013. Climate change 2013: The physical science basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK, and New York, NY: Cambridge University Press.
- Lawson, B.D., and Armitage, O.B. 2008. Weather guide for the Canadian Forest Fire Danger Rating System.
- Lee, B.S. 1995. The Canadian Wildland Fire Information System. Ninth Annual Symposium on Geographic Information Systems in Natural Resource Management, Vancouver, BC, March 27–30, 1995, 639–646.
- Turner, J.A., and Lawson, B.D. 1978. Weather in the Canadian Forest Fire Danger Rating System (Information Report BC-X-177). Victoria, BC: Canadian Forestry Service.
- Van Wagner, C.E. 1987. Development and structure of the Canadian Forest Fire Weather Index System (Forestry Technical Report 35). Ottawa, ON: Canadian Forestry Service.
Canadian Forest Service key contacts
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
- Flannigan, M.D., Amiro, B.D., et al. 2006. Forest fires and climate change in the 21st century. Mitigation and adaptation strategies for global change 11, 847–859.
- Flannigan, M., Cantin, A.S., et al. 2013. Global wildland fire season severity in the 21st century. Forest Ecology and Management 294, 54–61.
- Kochtubajda, B., Flannigan, M.D., et al. 2006. Lightning and fires in the Northwest Territories and responses to future climate change. Arctic 59, 211–221.
- Lawson, B.D., and Armitage, O.B. 2008. Weather guide for the Canadian Forest Fire Danger Rating System (Catalogue No. Fo134-8/2008E-PDF). Edmonton, AB: Canadian Forest Service.
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