National Fire Danger Rating System
This is the NFDRS Fire Index used by the National Forest Service:
The Chandler Burning Index (CBI) uses the air temperature and relative humidity to calculate a numerical fire index of the fire danger at that exact moment in time. The Chandler Burning Index has been shown to be highly correlated with monthly fire activity, but it does not take into consideration the long-term fuel situation and is not a good indication of the fire dangers. This is why the National Forest Service and other Federal and State agencies use the National Fire Danger Rating System (NFDRS).
The National Fire Danger Rating System (NFDRS) is the best method to forecast the real fire danger which uses the Energy Release Component (ERC) or the Burn Index (BI). Some stations use ERC and others use BI for calculating the Fire Danger Rating. They have a chart that uses Staffing Levels (STL or SL) and the Ignition Component (IC) to derive the Adjective Fire Ratings of Low, Moderate, High, Very High, and Extreme. You can download the Appendix and go to Page 11 to see how the Fire Danger Color Codes are derived.
There are two URL's that the National Forest Service Wildfire Assessment System use. The Weather Information Management System (WIMS) publishes these each day at 0115 UTC (They say 0000 UTC, but it is about 0115 UTC before it shows up on their web page.). One is the Observed numbers and the other is the Forecast numbers for the next day. These programs use the text files on these two web pages to derive the data on these NFDRS Fire Danger pages. The programs read the two text files and parse just the data needed for this location. The two URL's are:
Managers at the National Forest Service use the National Fire Danger Rating System (NFDRS) to input data and to receive information used to determine fire danger in their area. Based on the fire danger, managers may impose restrictions or closures to public lands, plan for or pre-position staff and equipment to fight new fires and to make decisions whether to suppress or allow fires to burn under prescribed conditions. NFDRS components:
The Adjective Class Fire Danger Rating should only be utilized for public information. Staffing Level (SL or STL) is used for in-house fire readiness.
Using the IC, the SL (STL), and the Adjective Fire-Danger Matrix, WIMS determines the Fire Danger Rating (R). Adjective Fire-Danger is expressed as one of five levels:
The processors that calculate fire danger automatically calculate the adjective class rating using information provided by the user when establishing their weather station parameters. The adjective rating calculations are keyed off the priority one fuel model listed in your station record. It uses the staffing index, such as ERC or BI, the user associates with that first fuel mode/slope/grass type/climate class combination entered.
The actual determination of the daily adjective rating is based on the current or predicted value for a user selected staffing index and ignition component using the table below.
Legend for NFDRS Tables:
- Date = Date
- Stn# = Station Number
- Station = Station Name
- St = State
- Elev = Elevation
- Lat = Latitude
- Long = Longitude
- Mdl = Model Number
- Tmp = Temperature
- RH = Relative Humidity
- Wind = Wind Speed in MPH
- PPT = Precipitation - Observed or Forecast Precipitation Hours
- ERC = Energy Release Component - Based upon the estimated potential available energy released per unit area in the flaming zone of a fire. It is dependent upon the same fuel characteristics as the spread component (SC). The day to day variations of the ERC are caused by changes in the moisture contents of the various fuel classes, including the 1000 hour time lag class. ERC is derived from predictions of the rate of heat release per unit area during flaming combustion and the duration of the burning. Expressed in BTU's per square foot.
- BI = Burning Index - A measure of fire intensity. BI combines the Spread Component and Energy Release Component to relate to the contribution of fire behavior to the effort of containing a fire. BI has no units, but in general it is 10 times the flame length of a fire.
- SC = Spread Component - A rating of the forward rate of spread of a head fire. It integrates the effect of wind, slope, and fuel bed and fuel particle properties. The daily variations are caused by the changes in the wind and moisture contents of the live fuels and the dead fuel timelag classes of 1, 10, and 100 hr.
- KBDI = Keetch-Byram Drought Index - A number between 0-800 representing the amount of moisture in the top 8 inches of soil. Zero is saturated, 800 is maximum drought stress. It is calculated from recent precipitation measurements in relation to the average annual precipitation. It is important to note that the KBDI is customized for each geographic area and that often the scale shows less of a range in variation. (-99 = No Annual Precip for Station)
- HUN = 100 Hour Fuel Moisture - This value represents the modeled moisture content of dead fuels in the 1 to 3 inch diameter class. It can also be used as a very rough estimate of the average moisture content of the forest floor from three-fourths inch to 4 inches below the surface.
- THOU = 1000 Hour Fuel Moisture - The dead fuel moisture levels are computed from a 7-day average boundary condition composed of day length, hours of rain, and daily temperature/humidity ranges. Fuel sizes range from 3 to 6 inches in diameter.
- TEN = 10 Hour Fuel Moisture - Computed from observation time temperature, humidity, and cloudiness. Can also be an observed value, from a standard set of fuel sticks that are weighed as part of the fire weather observation. Fuel Sizes range from 0.25 to 1 inch in diameter
- STL or SL = Staffing Level - A component of the NFDRS relating to the level of fire management staffing. Staffing levels are from 1-5 with 1 being the lowest and 5 the highest.
- ADJ = Adjective Fire Danger Rating - A public information component of the NFDRS specific to the rating of fire danger. Adjective ratings are: low(L), moderate(M), high(H), very high(V) and extreme(E).
- IC = Ignition Component - Related to the probability of a firebrand producing a fire that will require suppression action. It is mainly a function of the 1 hour time lag (fine fuels) fuel moisture content and the temperature of the receptive fine fuels. IC has no units. A percentage of probability from 1-100.
- Staffing = Staffing Specifications for this Station - Shows the Staffing Method used by each Station to calculate by either ERC or BI and the 5 associated values at the 97th, 90th, 66th and 24th percentiles.