Data Values information

Fuel Types

Predicting the potential behavior and effects of wildland fire is an essential task in fire management. Mathematical surface fire behavior and fire effects models and prediction systems are driven in part by fuelbed inputs such as load, bulk density, fuel particle size, heat content, and moisture of extinction. To facilitate use in models and systems, fuelbed inputs have been formulated into fuel models. A fuel model is a set of fuelbed inputs needed by a particular fire behavior or fire effects model.

AratosFire uses the fuel models as they are described by Scott and Burgan. Fuel Types are as follows:

  • NB, nonburnable
  • GR, grass
  • GS, grass shrub
  • SH, shrub
  • TU, Timber Understory
  • TL, Timber Litter
  • SB, Slash Blowdown
The NB fuel models are not used in AratosFire. User can select from a variety of 54 fuel models depending on the fuel model which better describes his area of interest. Take a look at the fuel types which are used in AratosFire here.

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Wind Speed and Direction

The user can set the wind speed and direction. The wind speed is given in miles per hour (mph) while the wind direction in degrees. User can select one of the 8 default wind directions or set its own by using the spin box.

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Slope and Aspect

Slope is a measure of change in surface value over distance. User has to give a value from 0 to 100 (%). Aspect is the direction to which a mountain slope faces. Taking a bearing on the fall-line of a slope is a useful method of identifying which side of a hill you are on.

  1. Stand facing downhill - the way a ball would roll if set away down the hill.
  2. Point your compass in the direction of the fall-line - i.e. with direction of travel indicator pointing downhill. This is the aspect direction.
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Moisture Values

Moisture is described by 6 parameters. The four of them are known as the dead fuel parameters while the rest of them are the live fuel parameters.

The dead fuel parameters are:

  • Dead1h (< 0.625 cm (0.25 in.) diameter) 1-hour time lag fuels are the most important for carrying surface fires and their moisture content governs fire behavior. One-hour fuels include fallen needle and leaf litter, grassy fuels, lichens, and small twigs. Within this category, response times vary by fuel type. Lichen, grass, and well-cured needles respond to changes faster than freshly fallen needles and hardwood leaves. Due to their high surface area to volume, low moisture content, and location in the combustion zone, they produce little smoke and have low flame residence time.
  • Dead10h (0.625 - 2.5 cm (0.25 to 1 in.) diameter) Common 10-hour fuels include small branches and woody stems. Due to their resistance to drying and greater heat capacity, 10-hour fuels often do not combust in low-intensity surface fires. When moisture is low, however, 10-hour fuels can carry hot fires and help ignite larger (100- and 1000- hour) fuels. Ten-hour fuels are readily consumed when fuel moistures are low.
  • Dead100h (2.5 cm - 7.6 cm (1 - 3 in.) diameter) Larger downed woody debris is common 100-hour forest fuels. These fuels take longer to dry, deterring their consumption under most conditions. Likewise, 100-hour fuels are slow to gain moisture, so they can combust after prolonged drought, even with recent precipitation.
  • Dead1000h (> 7.6 cm (3 in.) diameter) These fuels, which include large downed branches, logs, and tree stumps, burn only under prolonged dry conditions, or when sufficiently pre-heated by adjacent fuels. Since they do not commonly burn, 1000-hour fuels can act as firebreaks and cause fire shadows.
  • TU, Timber Understory
  • TL, Timber Litter
  • SB, Slash Blowdown
    The live fuel parameters are:
  • Live Herb
  • Live wood
The dead fuel parameters take a value from 0.01 to 0.5 while the live fuel parameters take a value from 0.3 to 3.0.

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