LESSON 3 - EFFECTS OF WEATHER, TOPOGRAPHY AND FUELS ON FIRE BEHAVIOR
3.2 Fire Weather Index System
The Fire Weather Index System (FWI) is one component of a much larger structure ( Canadian Forest Fire Danger Rating System) that was developed to help fire managers determine the level of fire danger. Scientists looked at fire dynamics and it became obvious that weather was an extremely critical factor in its development. Through the work of numerous people, and over a period of many years, the FWI became a reality in Canada. In the early 70's fire managers began using the system, and 30 years later, it is still an extremely valuable tool.
In order for the system to work, weather information must be gathered at 1:00 p.m.(local day light time) and this is used to provide fire managers with greater awareness about fire potential. Weather information gathered includes the following: Temperature, Relative Humidity, Amount of Precipitation, Wind Speed ( 10 minute average from a height of 10 metres) and Wind Direction.
F.W.I. can provide a variety of information on danger levels, but the information is a numerical rating and therefore information had to be grouped together so that a verbal indication can be given that anyone can understand. The groups that are used in Nova Scotia are Low, Moderate, High and Extreme. In the case of other agencies, groups have been further broken down even finer ( very low & very high).
The information derived from the system can provide fire managers with the knowledge about two distinct areas: FUEL MOISTURE CONTENT and GENERAL FIRE BEHAVIOR. Fuel moisture Codes indicate the three levels of fuel moisture on and below the surface. Fire behavior Indices indicate general information regarding fire behavior ( rate of spread, intensity levels ).