Canadian Forest Fire Weather Index (FWI) System
Canadian Forest Fire Weather Index (FWI) System : A subsystem of the Canadian Forest Fire Danger Rating System; referred to previously by a variety of names (e.g. Canadian Forest Fire Weather Index, Canadian Fire Weather Index, Canadian Forest Fire Weather Index Tables). The components of the FWI System provide numerical ratings of relative fire potential in a standard fuel type (i.e. a mature pine stand) on level terrain, based solely on consecutive observations of four fire weather elements measured daily at noon (1200 hours local standard time or 1300 hours daylight saving time) at a suitable fire weather station; the elements are dry-bulb temperature, relative humidity, wind speed, and precipitation. The system provides a uniform method of rating fire danger across Canada. The FWI System consists of six components. The first three are fuel moisture codes that follow daily changes in the moisture contents of three classes of forest fuel; higher values represent lower moisture contents and hence greater flammability. The final three components are fire behaviour indexes representing rate of spread, amount of available fuel, and fire intensity; their values increase as fire weather severity worsens. The six standard codes and indexes of the FWI System are: (1) Fine Fuel Moisture Code (FFMC): A numerical rating of the moisture content of litter and other cured fine fuels. This code indicates the relative ease of ignition and flammability of fine fuel. (2) Duff Moisture Code (DMC): A numerical rating of the average moisture content of loosely compacted organic layers of moderate depth. This code indicates fuel consumption in moderate duff layers and medium-sized woody material. (3) Drought Code (DC): A numerical rating of the average moisture content of deep, comp act, organic layers. This code indicates seasonal drought effects on forest fuels, and the amount of smouldering in deep duff layers and large logs. (4) Initial Spread Index (ISI): A numerical rating of the expected rate of fire spread. It combines the effects of wind and FFMC on rate of spread but excludes the influence of variable quantities of fuel. (5) Buildup Index (BUI): A numerical rating of the total amount of fuel available for combustion that combines DMC and DC. (Referred to as the Adjusted Duff Moisture Code or ADMC between 1969 and 1975). (6) Fire weather Index (FWI): A numerical rating of fire intensity that combines ISI and BUI. It is suitable as a general index of fire danger throughout the forested areas of Canada
No records Found