Fuel Moisture Definitions

Dead Fuel Moisture

This is the moisture content of dead organic fuels, expressed as a percentage of the oven dry weight of the sample, that is controlled entirely by exposure to environmental conditions.

Hundred Hour Dead Fuel Moisture (100hr)

The 100 hour fuel moisture 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.

Thousand Hour Dead Fuel Moisture (1000hr)

1000-Hour 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.

Energy Release Component(ERC)

The Energy Release Component (ERC) is an NFDRS (National Fire Danger Rating System) index related to how hot a fire could burn. It is directly related to the 24-hour, potential worst case, total available energy (BTUs) per unit area (in square feet) within the flaming front at the head of a fire.

The ERC can serve as a good characterization of fire season as it tracks seasonal fire danger trends well. The ERC is a function of the fuel model and live and dead fuel moistures. Fuel loading, woody fuel moistures, and larger fuel moistures all have an influence on the ERC, while the lighter fuels have less influence and wind speed has none. ERC has low variability, and is the best fire danger component for indicating the effects of intermediate to long-term drying on fire behavior (if it is a significant factor) although it is not intended for use as a drought index.

Charts from each Forest Service severity weather station are arranged generally from the northern part of the Geographic Area to the southern part. Severity stations are those weather stations which represent the fire danger conditions on the Forest Unit, and most stations contain at least twenty years of historical weather data. Data collected prior to 1976 is not used in these analyses due to an issue with the relative humidity measurements before that time.