U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3121

September 2012

Geographic Analysis and Monitoring Program

United States Geological Survey Fire Science—Fire Danger 

Monitoring and Forecasting

Printed on recycled paper

The convergence of large amounts of dry wildland fuels 

and weather favorable for fire ignition and spread signifies high 

potential for uncharacteristically large and dangerous fires. The 

ability to characterize the potential for hazardous fire activity requires measurements of fuel condition combined with 

information from weather forecasts. The availability of long 

fire histories adds a third dimension, fire probability, which can 

improve the ability to develop weekly forecasts of the location 

and number of large fires over a given region (Preisler and others, 2008). 

The United States Geological Survey (USGS) uses moderate resolution satellite data to assess live fuel condition for 

estimating fire danger. Using 23 years of vegetation condition 

measurements, we are able to determine the relative greenness 

of current live fuels. High relative greenness values indicate the 

Figure 1. This relative greenness image for July 10–16, 

2012, shows how green this time period is relative to the 

maximum greenness over the course of a year. High relative 

greenness percentages indicate substantial amounts of 

green and healthy vegetation. Low percentages indicate 

vegetation that has not yet grown to its full seasonal 

potential, or vegetation that has already reached its 

maximum and is now drying up. Relative greenness images 

can be obtained from the U.S. Department of Agricultural 

Forest Service, Wildland Fire Assessment System (WFASMAPS).

Figure 2. The fire potential index (FPI) image for July 16, 2012, shows the 

areas most susceptible to fire ignition. The FPI index is scaled from 1–100, 

where 1 is the lowest potential and 100 is the highest potential.

vegetation is healthy and vigorous; low greenness values indicate the vegetation is under stress, dry (possibly from drought), 

behind in annual development, or dead. Forest, shrub, and 

grassland vegetation with low relative greenness are susceptible 

to fire ignition during the fire season. The relative greenness for 

July 16, 2012, is shown in figure 1.

The fire potential index (FPI) integrates weather information from the National Digital Forecast Database (http://www.

nws.noaa.gov/ndfd/) and satellite-derived vegetation condition 

information, and is used to identify the areas most susceptible 

to fire ignition (Burgan et.al., 1998). The combination of relative greenness and weather information provides an estimate 

of the moisture condition of the live and dead vegetation. The 

FPI provides local and regional fire planners with a quantitative measure of fire ignition risk. The FPI for July 16, 2012, is 

shown in figure 2. 

Each day, the USGS, in collaboration with the U.S. 

Forest Service, produces 7-day forecasts for all Federal lands 

of the distributions of number of ignitions, number of fires 

above a given size, and conditional probabilities of fires 

growing larger than a specified size (figure 3). 

The large fire probability map is an estimate of the likelihood that ignitions will become large fires, given existing 

levels of the fire danger variables. The large fire forecast map 

is a probability estimate of the number of fires on Federal 
lands exceeding 100 acres in the forthcoming week. The ignition forecast map is a probability estimate of the number of fires 

on Federal land greater than 1 acre in the forthcoming week. 

The extreme event forecast is the probability estimate of the 

number of fires on Federal land that may exceed 5,000 acres in 

the forthcoming week.

References

Preisler, H., Burgan, R., Eidenshink, J., and Klaver, J., 2008, 

Estimation and mapping of large wildfire probabilities based 

on satellite and gridded weather information: International 

Journal of Wildland Fire, v. 18, no. 5, p. 508–516. 

Burgan, R.E., Klaver, R.W., and Klaver, J.M., 1998, Fuel 

models and fire potential from satellite and surface observations: International Journal of Wildland Fire, v. 8, no. 3, p. 

159–170. 

National Weather Service, 2007, National Digital Forecast Database (NDFD): National Weather Service database, accessed 

August 21, 2012, at http://www.nws.noaa.gov/ndfd/.

Figure 3. The 7-day forecast maps for the week of July 16, 2012. The 

large fire probability shows the percent chance that a fire at least 

1 acre in size will grow to exceed 100 acres [based on present fire 

potential index (FPI) values]. The ignition forecast shows the 50th 

percentile forecast for the number of 1+-acre ignitions in the coming 

week on Federal land (based on historic fire occurrence frequencies). 

The large fire forecast shows the 50th percentile forecast for the 

number of 100+-acre fires in the coming week on Federal land (based 

on present FPI values and historic occurrence frequencies). The extreme event forecast shows the percent chance of at least one 

5000+-acre fire in the coming week on Federal land (based on present FPI values and historic occurrence frequencies).

For more information

Fire Science Web site: 

http://eros.usgs.gov/#/Science/Landscape_Dynamics/Fire_Science

Fire Danger Monitoring and Forecasting Web site:

http://firedanger.cr.usgs.gov/

For more specific fire danger project information

Jeff Eidenshink (eidenshink@usgs.gov) 

Stephen Howard (smhoward@usgs.gov)

U.S. Geological Survey

Earth Resources Observation and Science (EROS) Center

Mundt Federal Building

Sioux Falls, South Dakota 57198

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