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Fine fuel hazard levels are converted to an equivalent fine fuel load (t/ha). While coarser fuels are consumed during a fire, the combustion of fine fuels is the process that predominantly determines spread rates. Fuels are considered as three separate strata; surface (which includes near-surface fuels), elevated fuel and bark, in accordance with forest fuel measurement standards in Southern Australia (McCarthy et al. 1999; Hines et al. 2010). Fuel classes that have no elevated or bark fuels are considered by PHOENIX as grasslands and are processed using functions derived from the CSIRO grassland fire spread model (Cheney et al. 1998).
Table 3. PHOENIX fuel types currently recognised in southern Australia.
Veg Type | Code | FuelCode | Description | Fuel Characteristics |
|---|---|---|---|---|
Forest | F01 | 15 | Rainforest | dense vegetation with little dead material, epiphytes, vines, ferns, rarely dry |
| F02 | 32 | Wet Forest with rainforest understory | wet sclerophyll forest with a mesic understorey |
| F03 | 13 | Riparian Forest shrub | dense vegetation but with a small proportion of dead material |
| F04 | 11 | Wet Forest shrub & wiregrass | high biomass forest, but with little dead suspended material unless wiregrass present |
| F05 | 12 | Damp Forest shrub | dense understorey and potentially high bark hazard (karri) |
| F06 | 40 | Semi-mesic Sclerophyll forest | forest with semi-mesic shrubs and flammable grasses, sedge understorey |
| F07 | 33 | Swamp Forest | dense Melaleuca forest with little understorey |
| F08 | 6 | Forest with shrub | potentially high bark hazard, shrubs moderate flammability (mixed jarrah/karri) |
| F09 | 7 | Forest herb-rich | potentially high bark hazard, little elevated fuel |
| F10 | 45 | Dry Forest shrubs | dry forest with continuous understorey, (southern jarrah) |
| F11 | 8 | Dry Open Forest shrub/herbs | dry forest with open understorey (northern jarrah) |
Grass/sedges | G01 | 16 | High Elevation Grassland | dense sward of tussock grasses or herbs, high cover |
| G02 | 4 | Moist Sedgeland / Grassland | dense sward, potentially high dead component, button grass |
| G03 | 29 | Ephemeral grass/sedge/herbs | dense grass and sedges with potentially high levels of dead suspended material |
| G04 | 20 | Temperate Grassland / Sedgeland | grasses and sedges widespread, but varying in biomass |
| G05 | 44 | Hummock grassland | hummock grassland, discontinuous surface fuels |
Herbs | H01 | 30 | Moorland / Feldmarks | low flammability cushion plants |
| H02 | 36 | Alpine herbland | dense, upright, low flammability herbs |
| H03 | 34 | Wet herbland | freshwater herbs on mud flats |
| H03 | 37 | Wet herbland | low herbs in seasonally inundated lakebeds or wetlands |
Mallee | M01 | 27 | Mallee chenopod | low flammability except after exceptional rain bringing grasses |
| M02 | 42 | Mallee grass | mallee woodland with predominantly grass understorey |
| M03 | 25 | Mallee shrub/heath | continuous shrub layer but amount of dead material depending on species present |
| M04 | 26 | Mallee spinifex | discontinuous fuels, very flammable under windy conditions |
Bare | NIL | 0 | Water, sand, no vegetation | fuel absent |
Plantations | P01 | 98 | Softwood Plantation | dense canopy with continuous surface fuels |
| P02 | 99 | Hardwood Plantation | uniform canopy with continuous surface fuels |
Shrubs | S01 | 17 | High Elevation Shrubland/Heath | dense cover of shrubs with surface fuel largely under plants |
| S02 | 14 | Riparian shrubland | dense vegetation with little dead material |
| S03 | 35 | Wet Scrub | flammable shrubland with high level of dead elevated fuels |
| S04 | 1 | Moist Shrubland | dense shrubland, salt affected |
| S05 | 31 | Dry Closed Shrubland | tea-tree or paperbark thickets, little understorey |
| S06 | 21 | Broombush / Shrubland / Tea-tree | dense shrubland, but with relatively low level of dead material |
| S07 | 10 | Sparse shrubland | sparse shrubby vegetation with discontinuous surface fuels |
| S08 | 3 | Low flammable Shrubs | low flammability except after exceptional rain bringing grasses |
| S09 | 38 | Mangroves / Aquatic Herbs | trees, shrubs and herbs in permanent water, unburnable |
Heaths | S10 | 23 | Wet Heath | dense heath possibly with dense sedgy undergrowth |
| S11 | 24 | Dry Heath | dense heath with significant amounts of dead material |
Woodland | W01 | 18 | High Elevation Woodland shrub | wooded area with shrubby understorey |
| W02 | 19 | High Elevation Woodland grass | wooded area with continuous grass tussocks |
| W03 | 97 | Orchard / Vineyard | orchard or vineyard |
| W04 | 2 | Moist Woodland | low trees, shrubby, sedgy understorey, bark hazard |
| W05 | 22 | Woodland bracken/shrubby | wooded area with varying understorey, but not heathy |
| W06 | 9 | Woodland Grass/Herb-rich | surface fuels dominated by grass and herbs |
| W07 | 5 | Woodland Heath | flammable shrubs and high bark hazard |
| W08 | 41 | Gum Woodland heath/shrub | gum woodland with moderate bark hazard, heath/shrub understorey |
| W09 | 43 | Gum Woodland grass/herbs | gum woodland with moderate bark hazard, herbaceous understorey |
| W10 | 39 | Savanna grasslands | tall flammable grasses in an open woodland |
| W11 | 28 | Woodland Callitris/Belah | low flammability except after exceptional rain bringing grasses |
4.2 Wind reduction factors
| Section | |||||
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4.2.1 PurposeBureau of Meteorology forecast wind data is provided at 10 m above ground. PHOENIX takes this data and converts it to wind speeds at 1.5 m above ground for use by various PHOENIX models. 4.2.2 BasisWind reduction factors are specified by the user for each defined fuel type in the Fueltype.xml file (See Section 5.7: Fuel Accumulation). 4.2.3 Assumptions and limitationsIt is assumed that the wind at 1.5 m is the 'mid-flame height' wind speed which is clearly untrue for very low-intensity fires and very high-intensity fires. It also assumes that the wind reduction factor is a constant, but it is known to vary from day to night and with the magnitude of the wind speed in the open. |
4.2.4 User interactions
Wind reduction factors can only be changed by the user by redefining the fuel type characteristics in the Fueltype.xml file.
4.2.5 Description
Wind reduction factors are assigned to each fuel type in the fueltype.xml file. Values for the wind reduction factors are not well studied and so many will have to be estimated by an experienced fire behaviour scientist. Some guidance on the values of wind reduction factors can be gained from the Western Australian 'Red Book' (Sneeuwjagt and Peet 1998 p.30). The wind reduction factor is used to estimate the mid-flame height wind speed within the vegetation based on the observed or forecast wind speed measured at 10 m in the open. In 18 m high open eucalypt forest, McArthur assumed that the wind reduction factor at 1.5 m above the ground was a factor of 3. In Jarrah forest in Western Australia, Project Vesta found that the wind reduction factor at 5 m above the ground was also a factor of 3. In grassland, there is no wind reduction factor assumed so the value is set to 1. In grassy woodland in northern Australia, Cheney et al. (1998) found the wind reduction factor to be a factor of 2. Since flame height varies from low-intensity surface fires to high-intensity crown fires, the reality is that the wind reduction factor is not constant even for a single fuel type, but a single typical value is used. Work by Kangmin Moon (2016) developed a model of estimating the wind reduction factor in different fuel types at different heights which would enable the use of a dynamic wind reduction factor, but this has not yet been incorporated into PHOENIX.
The cell wind reduction factor is also used to estimate an approximate leaf area index (LAI) used to calculate shading based on Beer's law (Silberstein, Sivapalan et al. 2003). Refer to Section 5.6: Solar Radiation Model for further information on how shading is used.