The precipitation, relative humidity, wind speed, and temperature data collected from BC Wildfire Service's network of weather stations is used to determine fuel moisture and fire behaviour indices through the Fire Weather Index System component of the Canadian Forest Fire Danger Rating System (CFFDRS). A map of B.C. showing major towns and other features can be found at the bottom of this page for reference purposes.
Note: Where discrepancies exist between the colour display on the weather maps and the numerical values posted for the weather stations, the posted numerical values shall take precedence for the purpose of implementing the Wildfire Regulation.
The amount of precipitation has a significant impact on the moisture level in the fuels. Precipitation of 0.5 mm or less tends to be intercepted by the forest canopy preventing it from reaching the fuels on the forest floor.
Relative humidity refers to the ratio, in percent, of the amount of moisture in a volume of air to the total amount of moisture which that volume of air can hold at a given temperature and atmospheric pressure. The amount of moisture in the air affects the level of moisture in the fuels. Dry air (low relative humidity) will tend to dry out fine fuels, while moist air (higher relative humidity) will tend to add moisture to fine fuels.
Wind dries fuels by moving moisture laden air away from the fuels and replacing it with drier air which can then draw up more moisture, thereby continually drying the fuels. Wind speed influences the rate of fire spread. Burning embers can also be transported by wind and blown onto new fuels ahead of a fire.
Temperature also has an impact on fuel moisture and fire behaviour. Fuels heated by the sun will ignite more easily and burn faster than cooler fuels, while warmer air, which can hold more moisture than cooler air, can lead to increased drying of fuels.
Due to the significant amount of information displayed on fire weather maps, little other detail is displayed. Therefore, it can be helpful to compare the weather maps to a more detailed map (below) for orientation.
The Fire Weather Index System has six standard components that together provide a numeric rating to indicate the potential for a wildland fire to occur.
The first three components are fuel moisture codes, which indicate the moisture content of the forest floor and other dead organic matter. Their numeric values rise as the moisture content of these materials decreases. There is one fuel moisture code for each of three layers of fuel: litter and other fine fuels (Fine Fuel Moisture Code); loosely compacted organic layers of moderate depth (Duff Moisture Code); and deep, compact organic layers (Drought Code).
The remaining three components are fire behaviour indices, which represent: the rate of fire spread (Initial Spread Index); the fuel available for combustion (Buildup Index); and the frontal fire intensity (Fire Weather Index). These three values rise as the fire danger increases.
The Fine Fuel Moisture Code is a numeric rating of the moisture content of litter and other cured fine fuels. This code is an indicator of the relative ease of ignition and the flammability of fine fuel.
The Duff Moisture Code is a numeric rating of the average moisture content of loosely compacted organic layers of moderate depth. This code gives an indication of fuel consumption in duff layers (2-4 inches) deep and medium-sized woody material.
The Drought Code is a numeric rating of the average moisture content of deep, compact organic layers. This code is a useful indicator of the effects of seasonal drought on forest fuels and the amount of smouldering that may occur in deep duff layers and within large logs.
The Initial Spread Index is a numeric rating of the expected rate of fire spread. It is based on the wind speed and the Fine Fuel Moisture Code. Like the rest of the Fire Weather Index system components, the Initial Spread Index does not take fuel types into account. Actual spread rates vary between fuel types.
The Buildup Index is a numeric rating of the total amount of fuel available for combustion on the landscape. It is based on the Duff Moisture Code and the Drought Code, thus taking into account the moisture content of medium-sized to large-sized woody material as well as the effects of seasonal drought on forest fuels. The BUI is used by the BC Wildfire Service to decide when to implement a campfire ban.
- Multiple factors are taken into consideration when assessing wildfire hazards and deciding whether to implement an open fire prohibition, including: current and forecasted weather conditions; the availability of firefighting resources; and the Buildup Index (BUI).
- Campfire prohibitions are now implemented by the BC Wildfire Service based on a region’s BUI values. Previously, campfire bans were date-driven or based on Fire Danger Ratings, depending on the fire centre.
- A campfire ban will be enacted when over 50% of the weather stations within a defined geographic area surpass the BUI threshold established for that area.
- BUI thresholds vary throughout the province. The threshold for a given area is based in part on the area’s assigned “fuel type”, which indicates how volatile those fuels are, how intensely and deeply they will burn, and how difficult it might be to suppress a fire in that fuel type.
The Fire Weather Index is a numeric rating of fire intensity. It is based on the Initial Spread Index and the Buildup Index. It is used as a general index of fire danger throughout the forested areas of Canada.