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National Fire Danger Rating System

Status
Ongoing
Start Date
January, 1994

The National Fire Danger Rating System (NFDRS) uses weather, fuels, and fire occurrence data to calculate fire danger for a given area. Widely used across the United States, the NFDRS was recently updated to improve estimates of fuel moisture and simplify fuel model inputs. 

In the United States, the National Fire Danger Rating System (NFDRS) has been used to support operational fire decision making for the last 50 years. The NFDRS was first created in 1972, with updates in 1978 and 1988. The latest version (NFDRS2016) was released for operational, nationwide use in 2023. Daily outputs from the NFDRS are used to maintain wildland fire situational awareness, respond to wildfire incidents, plan for and safely conduct prescribed fires, and inform the public about wildfire potential (low to extreme) through signage commonly seen on National Forests. 

 

Fire danger rating sign
Photo Credit
USDA Forest Service

The National Fire Danger Rating System sign - a common sight across National Forests.

The NFDRS is made up of several parts – the fire danger rating model itself, and the system required to use it. In a nutshell, the NFDRS uses weather, fuels, and fire occurrence databases to feed the fire danger rating model, and user-interfaces to run the model and display the outputs in tables, maps, and graphs. NFDRS is operationally run through the Fire Environment Mapping System (FEMS). The software package FireFamily+ (FF+) is used to calculate fuel moistures and fire danger indices for the NFDRS. The Wildland Fire Assessment System (WFAS) collects and displays spatial fire danger information for federal, state, and local land managers across the United States. Land managers and other stakeholders must interpret the information, apply it in decision support tools, and ultimately make decisions on the ground. 

For more information on the history and components of the NFDRS and comparisons between early and updated versions of the fire danger rating model, read this publication: Modernizing the US National Fire Danger Rating System (Version 4): Simplified Fuel Models and Improved Live and Dead Fuel Moisture Calculations.

Principal Investigators:
W. Matt Jolly
Larry Bradshaw

Funding Contributor: USFS Fire and Aviation Management

Project Years: 1994-present

The NFDRS Model uses weather observations to estimate fuel moistures of various classes and categories of dead and live fuels. These fuel moistures are then combined with surface fuel loadings and site characteristics to estimate fire danger metrics that relate to the rate of spread, energy release and flame length of an initiating fire. The software package FireFamily+ (FF+) is used to calculate fuel moistures and fire danger indices for the NFDRS.

The NFDRS Model is composed of four primary modules: Inputs, Fuel Moisture Models, Fuel Models and Fire Danger Index Models. 

  • Inputs include measured weather data and local fuels and terrain characterizations. Weather inputs for NFDRS come from a network of over 2200 Remote Automated Weather Stations (RAWS) that are situated throughout the contiguous United States (CONUS), Alaska, Hawaii, Guam and Puerto Rico. All weather data are ingested into the Fire Environment Mapping System (FEMS) which maintains the data archive for all weather stations and performs all fire danger calculations. FEMS recently replaced the Weather Information Management System (WIMS) — read more about the transition here.
  • Fuel moisture models are the foundation of the NFDRS and the outputs from these models are combined and weighted with Fuel Models to calculate fire danger. Dead fuel moisture contents are calculated for four size classes (1-hr, 10-hr, 100-hr, 1000-hr). Live fuel moisture for herbaceous (grasses and forbs) and woody shrub (twigs and foliage) are estimated using the Growing Season Index model – an update from previous versions of the NFDRS.
  • Fuel models are used to weight the relative influence of each of the six fuel moisture contents on the final Fire Danger Index calculations. For each of the 4 dead fuel size classes and 2 live fuel categories, loadings and surface-area-to-volume ratios are specified and these are used in the Fire Danger Index Calculations. Early versions of the NFDRS used up to 20 fuel models that were shown to be redundant. The latest version uses only 5 unique fuel models, based on groupings of the original fuel models.
  • The Fire Danger Index Calculation produces metrics related to various aspects of the management and / or control of a wildland fire: Energy Release Component (ERC), Spread Component (SC), Burning Index (BI) and Ignition Component (IC). Later, the Severe Fire Danger Index (SFDI), a combination of the ERC and BI percentiles, was added to improve the model's ability to assess extreme events.

Key Personnel

Principal Investigators

Research Staff

Collaborators

  • Contributor(s):

    • USDA Forest Service Fire and Aviation Management
    • National Weather Service
    • IBM
    • Systems for Environmental Management

Publications

Last updated March 27, 2026
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