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The six standard components
of the FWI System provide numerical ratings of relative wildland fire potential.
The first three components are fuel moisture codes that follow daily changes
in the moisture contents of three classes of forest fuel with different drying
rates. For each, there are two phases - one for wetting by rain and one for
drying - arranged so that the higher values represent lower moisture contents
and hence greater flammability. The final three components are fire behaviour
indexes, representing rate of spread, amount of available fuel, and fire intensity;
their values increase as fire weather severity worsens.
The system is dependent
on weather only and does not consider differences in risk, fuel, or topography.
It provides a uniform method of rating fire danger throughout New Zealand. The
six components are described below.
FFMC - Fine Fuel
Moisture Code
A numerical rating of the
moisture content of litter and other cured fine fuels. This code is an indicator
of the relative ease of ignition and flammability of fine fuel.
DMC - Duff Moisture
Code
A numerical rating of the
average moisture content of loosely compacted organic layers of moderate depth.
This code gives an indication of fuel consumption in moderate duff layers and
medium-size woody material.
DC - Drought Code
A numerical rating of the
average moisture content of deep, compact, organic layers. This code is a useful
indicator of seasonal drought effects on forest fuels, and amount of smouldering
in deep duff layers and large logs.
ISI - Initial Spread
Index
A numerical rating of the
expected rate of fire spread. It combines the effects of wind and FFMC on rate
of spread without the influence of variable quantities of fuel.
BUI - Buildup Index
A numerical rating of the
total amount of fuel available for combustion that combines DMC and DC.
FWI - Fire Weather
Index
A numerical rating of fire
intensity that combines ISI and BUI. It is suitable as a general index of fire
danger throughout the forested and rural areas of New Zealand.
Fire Weather Observations
Temp - Temperature
Temperature @ 1300 hrs
RH - Relative Humidity
A numerical measurement
of air moisture saturation.
Dir - Wind Direction
360o |
North |
90o |
East |
180o |
South |
270o |
West |
RN24 - Rainfall
in last 24 hours
Rainfall in last 24 hours
measured in millimetres.
A "rain day" > 6.0 mms.
Wsp - Wind Speed
Measure
Wind speed measure @ km's
ph 10 meters above ground.
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