NATIONAL FIRE DANGER RATING SYSTEM (NFDRS)
- Energy Release Component (ERC) Charts -
How are the Charts used?
All wildland protection agencies are directed to protect life, property, and natural resources entrusted to them. These requirements dictate strict attention be paid to the availability and use of suppression resources. In the Southwest Area, the Charts are averaged over 3-day periods. They are primarily used to look at the seasonal trends, a comparison tool against previous years, and as one tool used in determining the Area preparedness level. Each chart displays the current year BI or ERC values relative to the average for a 25-year period, the average of the highest values during the same period, and when the values reach the 90th and 97th percentiles. The Charts are not designed to be site specific, they provide only a general picture of how conditions are currently and how the season is progressing in the Southwest. Units throughout the SWA produce their own local, site specific chart(s).
The Charts are only one of the components used in determining the SWA preparedness level. Other components that must be considered include; (1) current and long range forecasted weather affecting current and forecasted fire behavior/potential, (2) resource committments to incidents, (3) individual agency fire reports, (4) National Preparedness Level, (5) air quality considerations, and (6) fire suppression resource availability. The breakpoints in which the ERC Curve is used to assist in determining the area preparedness level are indicated by lines drawn horizontally (i.e. PL-2, PL-3, PL-4) on the chart. The 90th corresponds to the "very high" adjective reading and the 97th percentile corresponds to the "extreme" adjective reading.
How are the charts
There are 12 Automated Weather Stations (AWS) strategically located throughout the National Forests of the Southwest Area that collect data hourly throughout the year. Each day around 1300 local time, this data is uploaded via satellite to the National Weather Information System (WIMS) every hour. On Tuesday and Friday of each week, the data is downloaded from WIMS and inserted into the FireFamily Plus 4.0 software program, where the charts are derived.
The 12 stations are:
|4.||AZ||Iron Springs||20501||Prescott NF|
|8.||NM||Jemez||290702||Santa Fe NF|
What is the Burning
The Burning Index (BI) is a number related to the contribution of fire behavior to the effort of containing a fire. It is derived from the spread and energy release components (Spread Component and Energy Release Component). The rate of fire spread and the energy released in the flaming zone, considered together, are the measns of rating the difficulty of containment. The Bi is liinearly reated to the length of flames at the head of the fire. It is calculated from the SC and ERC using the relationships originally developed by Byram for calculating flame length (Byram 1959).
What is the Energy Release
The Energy Release Component (ERC) is based on the estimated potential available energy released per unit area in the flaming front of a fire. The day-to-day variations of the ERC are caused by changes in the moisture contents of the various fuel classes, including the 1,000 hour timelag class. The ERC is derived from predictions of (1) the rate of heat release per unit area during flaming combustion and (2) the duration of flaming.