Keetch-Byram Drought Index (KBDI):
This is a drought index that is specifically related to fire potential. The KBDI is broken into four categories which indicate the susceptibility of ground fuels to fire danger. The table in the right hand column indicates what the categories mean.
Dead Fuel Moisture:
Dead fuel moisture responds solely to ambient environmental conditions and is critical in determining fire potential. Dead fuel moistures are classed by time lag. A fuel's time lag is proportional to its diameter and is loosely defined as the time it takes a fuel particle to reach 2/3's of its way to equilibrium with its local environment. Dead fuels in NFDRS fall into four classes (1-hour, 10-hour, 100-hour, and 1000-hour); however, when looking at droughts usually only the 100-hour and 1000-hour fuel moisture are watched.
100-hour Dead Fuel Moisture: Measured from fuels which are 1 to 3" in diameter. Computed from 24-hour average boundary condition composed of day length, hours of rain, and daily temperature/humidity ranges.
1000-hour Dead Fuel Moisture: Measured from fuels which are 3 to 8" diameter. Computed from a 7-day average boundary condition composed of day length, hours of rain, and daily temperature/humidity ranges.