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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 interactionsWind reduction factors can only be changed by the user by redefining the fuel type characteristics in the Fueltype.xml file. |
4.2.5 Description
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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.
4.3 Fire history
| Section | |||||
|---|---|---|---|---|---|
4.3.1 PurposeFuel types are used in conjunction with the fire history layer to generate fuel levels at the time of the simulation. Based on the time of ignition specified by the user, fuel levels are calculated through the combination of fuel type and the time since the last fire using fuel accumulation curves defined in the fuel type conversion file. 4.3.2 BasisThis layer is based upon fire history provided by the user. 4.3.3 Assumptions and limitationsIn the case of overlapping fire histories, PHOENIX only uses the most recent fire occurrence. 4.3.4 User interactionsPHOENIX uses the fuel accumulation model (see Section 5.7: Fuel Accumulation) to calculate fine fuel hazard classes which are then converted to an equivalent fuel load (t/ha) for surface, elevated and bark fuels. The accumulation curves are part of the fuel type conversion file. The user can upload a supplementary fire history layer to PHOENIX to capture recent fire events or to explore the effect of hypothetical fires in the landscape. |
4.3.5 Description
Fuel types are used in conjunction with a user-provided fire history layer to create fuel layer information used in PHOENIX simulations and stored in the Fire Grid. The time since the most recent fire is used to estimate fuel levels using negative exponential accumulation curves (discussed in Section 5.7: Fuel Accumulation). As data is retained for only the most recent fires (see Figure 9), where historic fires are being simulated, the fire history layer must be adjusted to be representative of the appropriate conditions.
Figure 9. Diagram of how PHOENIX treats overlapping fire history. On the left, two fires have been mapped, one in 1972 and the other in 1985. On the right, a new fire in 2008 has overlapped these earlier fires and has replaced their fire history in the overlapping areas.
ESRI Shapefiles can be used to supplement the baseline fire history layer for particular simulation runs. This provision is made to account for fires that have occurred since the baseline fire history was processed or to enable hypothetical prescribed burning scenarios to be quickly evaluated. The supplementary fire history is added to any existing fire history layer and processed in the same manner as the fire history stored in the Fire Grid.
4.4 Topography
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4.4.1 PurposeA digital elevation model (DEM) is required by PHOENIX to support various models, such as slope correction, wind field models and map reprojection. 4.4.2 BasisAn ASCII grid DEM provided by the user with values represented as heights above sea level. 4.4.3 Assumptions and limitationsThat the DEM is accurate. 4.4.4 User interactionsPreparation and provision of input data. |
4.4.5 Description
From the DEM, elevation, slope and aspect are determined using bilinear interpolation with neighbouring cell values during a simulation. Bilinear interpolation is a common texture mapping technique.