Fire Potential / Fire Danger Maps
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Current Conditions
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Forecast
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Image Archive
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Data Archive
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Lightning Ignition Efficiency
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US48
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Lightning fires are started by strikes to ground that have a
component called a continuing current. All positive discharges have
a continuing current, and about 20% of negative discharges have
one. Ignition depends on the duration of the current and the kind
of fuel the lightning hits. Ignition in fuels with long and medium
length needle cast, such as Ponderosa pine and Lodgepole pine,
depend on the fuel moisture. Ignitions in short- needled species,
such as Douglas fir depend far more on the depth of the duff layer
than on the moisture. Spread of the fire after ignition usually
depends on fuel moisture in all cases.
The ignition efficiency on a 1 km pixel is given on a per discharge
basis. That is, if the efficiency is high, then about 9 discharges
will result in one ignition; if the efficiency is extreme, about 5
or fewer discharges will result in an ignition. The ratio of
positive and negative discharges is built into the calculation.
(Latham and Schlieter 1989) document the
algorithm.
The fuel type and depth are conversions of the 1 km resolution
current cover type (Hardy and others 1999)
for this specific calculation. The moisture input is the 100-hr
dead fuel moisture.
August 2002 - The lightning ignition efficiency algorithm has
been corrected due to discovery of an error. The resulting maps
reflect higher lightning efficiency than previously.