Fire Danger Rating, 2005

In Canada, fire danger is monitored using the Canadian Forest Fire Danger Rating System (CFFDRS) developed by the Canadian Forest Service. The CFFDRS comprises two primary subsystems: the Canadian Forest Fire Weather Index (FWI) System and the Canadian Forest Fire Behavior Prediction (FBP) System.

Fire danger rating is the process of systematically evaluating and integrating the factors that determine the ease of a fire starting and spreading, the difficulty of control, and the resulting impacts based on an assessment of ignition risk, the fire environment (fuels, weather, and topography) and values at risk. Fire danger rating systems produce indexes of fire potential that are used as a guide in a wide variety of fire management applications.

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Figure 1. Diagram of the Canadian Forest Fire Danger Rating System

Fire Weather Index (FWI) System

The FWI System provides estimates of fire danger based on a continuous record of weather observations taken daily at noon. The continuity of the record is required to track the moisture content of fuels (combustible material). Moisture content is estimated for fine fuels (twigs, leaves and needle litter), duff (loosely compacted organic layers of moderate depth) and drought (deep, compact organic layers). Temperature, relative humidity, wind speed and rainfall are inputs to the system. Wind speed and temperature directly influence a fire the most; however, rainfall is most important in determining fuel moisture. Frequently, the current weather conditions are not a good indicator of the fire hazard. The hazard would be much higher on a hot, windy day after a week of dry weather than it would be on a similar day after a week of rain.

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Figure 2. Structure of the Fire Weather Index System

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Figure 3. Tracking Daily Fuel Moisture

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Figure 4. Average Fire Weather Index values across Canada

Fire Behavior Prediction (PBP) System

The FBP System uses fuel type and terrain (elevation, slope, aspect) data, along with the weather-based Fire Weather Index (FWI) system outputs, to make predictions of fire spread rate, fuel consumption, and fire intensity. Unlike the codes and indices of the FWI System, these predictions are quantitative, that is, they are measurable quantities. For example, the spread rate is in meters per minute. The system uses 16 different fuel types, which are distinguished by characteristics of the vegetation and forest floor. Fire behavior is strongly influenced by the size and arrangement of fuels. For example, fine fuels such as needles and twigs ignite more readily than heavy fuels such as tree trunks.

Fire weather and fire behavior are monitored across Canada by provincial and park agencies, and nationally by the Canadian Forest Service. The Canadian Wildland Fire Information System provides maps of the major FWI and FBP System outputs for the whole country every day during the fire season (approximately May through September).

Fire Danger Rating Map

The fire danger rating in this map is based on the Fire Weather Index (FWI), an indicator of the predicted fire intensity. For clarification, the FWI is a component of the FWI System (see the structure diagram above). Because the FWI is independent of fuel type, different intensities can be expected in different fuel types at the same FWI. The FWI is probably best known from signs like this one that can be found in forested areas all over Canada.

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Fire Hazard Sign

Making maps of fire danger based on weather observations requires interpolation between weather stations. This works well for temperature and relative humidity, which typically change slowly over time and distance, but not so well for precipitation. Rainfall amounts can vary significantly even over short distances. It could rain heavily near a weather station, and not at all right at the station location. In this case, the interpolation would not give accurate results. Better results could be achieved with precipitation radar, but this is not (yet) available for most of the forested areas of Canada.

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Weather station

In the fire danger rating map, the FWI values have been classified into groups. In a representative fuel type (a pine forest), the following fire behavior can be expected:

• Low: smoldering or self-extinguishing fire. Flame height: less than 10 centimetres.
• Medium: creeping or gentle surface fire. Direct manual attack by firefighters with hand tools and water is possible. Hand-constructed fire guard should hold. Flame height: up to 1 metre.
• High: moderately vigorous surface fire. A hand-constructed fire guard will probably fail. Heavy equipment (bulldozers, pumpers, aircraft) are generally successful in controlling the fire. Flame height: up to 2 metres.
• Very high: intense surface fire. Frequent torching is possible. Control efforts at the fire's head may fail. Flame height: up to 3 metres.
• Extreme: crown fire. Control very difficult. Suppression action restricted to the fire's flanks. Indirect attack with aerial ignition (backfiring) may be effective. Flame height: 3 to 25 metres or more.

Note:

• These are national fire danger rating classifications, and may not be the same as provincial classifications. Each province determines its own classes according to their own policies and the fire weather characteristics of the area.
• The weather data used is obtained from the Meteorological Service of Canada stations, not from provincial stations. As a result, values may differ slightly from those obtained by individual provinces. The provinces have their own weather station networks, with a much higher station density than the national network. Also, each province does its own FWI calculations based on the standards and practices for that province.

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Figure 5. The Meteorological Service of Canada Operates 600 Stations Nationwide

• Forest Fire Hotspots, 2005 Map | Read about this map
• Forest Fire Hotspots, 2004 Map | Read about this map
• Forest Fire Hotspots, 2003 Map | Read about this map
• Forest Fire Hotspots, 2002 Map | Read about this map
• Forest Fire Hotspots, 2001 Map | Read about this map

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