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
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.