The Mount Soil Dryness Index (SDI) is calculated using the 24 hour rainfall and maximum temperature to 9 am each day and is an indicator of the amount of rainfall (in mm) required to saturate the top layer of soil within a forested area.
The Mount SDI value varies, depending on what type of forest canopy is assumed. For locations in the Mount Lofty Ranges and Lower South East districts, the Mount SDI is representative of a pine plantation (indicated by the darker green shading in the table above). For the remaining locations (olive green shading), the calculated Mount SDI is representative of an open eucalypt forest.
For full details, see the paper by A. B. Mount, "The derivation and testing of a soil dryness index using run-off data", published as Bulletin Number 4 by the Forestry and Timber Bureau, Canberra, August 1967.
The Drought Factor (DF) calculation is based on the rainfall record over the past 20 days and the current Mount SDI.
For full details, see the paper by D. Griffiths, "Improved Formula for the Drought Factor in McArthur's Forest Fire Danger Meter" published in the Australian Foresty Journal, Vol 62, No 2, pp 202-206 (1999).
Drought Factor.
This is a broad measure of fuel avalilability as determined by drought index and recent rainfall. Where the effect of one reain peios is superimosed on another, use the lowest drought factor.
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