Development and Structure of the Canadian Forest FireWeather Index System

The Canadian Fores t Fire Weather Index (FWI) was issued in 1970 after several years ' work by a number of fire researchers in the Canadian Fores try Service. The bes t features of the former fire danger index were incorporated in the FWI, and a link was preserved between old and new. The FWI is based on the moisture content of three classes of forest fuel plus the effect of wind on fire behavior. It consists of s ix components: three primary subindexes repres enting fuel moisture, two intermediate subindexes repres enting rate of spread and fuel consumption, and a final index represent ing fire intensity as energy output rate per unit length of fire front. The FWI refers primarily to a standard pine fuel type but is useful as a general index of fores t fire danger in Canada. It is determined every day from noon weather readings only: temperature, relative humidity, wind speed, and rain (if any). This paper des cribes the development of the Fire Weather Index, the