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Using
Humidity or Solar Radiation to Predict Fire Behavior
What
effect does humidity have on forest fuels?
- The
humidity establishes the baseline fuel moisture content of fuels
according to the time lag Fuel moisture content of the forest
fuel.
- Humidity
readings and fuel moisture computations or measurements are useful
to determine the fire behavior potential when no other heating
force is present in the fuel bed.
- Humidity
readings used to determine the fuel moisture in 1 and 10 hour
time lag fuels are most accurate at night, under cloud cover or
under heavy canopy.
What
effect does solar radiation have on the baseline fuel moisture content
in the fuel bed?
- Fuels
exposed to solar heating are heated and dried beyond the humidity's
influence.
- Forest
fuel beds become highly variable in temperature and moisture content
due to the variation of solar heating within the fuel bed.
- Available
fuels heated by radiation do not follow the time lag formula of
1 and 10 hour fuels, but change within minutes not hours.
- The
variation of fuel temperature is the cause of the variation in
fuel flammability, during daytime hours
How
does one see the effects of solar heating of fuels?
- Compare
the fire behavior under night time and daytime conditions or the
fire behavior variation on a heated aspect vs. a shaded aspect.
Literature
cited:
G. Byram & G. Jemison
1943 Solar Radiation and Forest Fuel Moisture
Journal of Agriculture Research Vol. 67-4 pages 149 - 176
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