Bushfire Hazard Assessment

Bushfire Hazard Assessment
14 Serenity Close, Noosa Heads



6.1.2     LANDSCAPE SLOPE


Landscape slope was created from a 25m resolution digital terrain model (DTM) by
calculating the maximum slope (in degrees) from the central pixel in a group of 9 x 9 cells
to the eight (8) adjoining cells in that group.

Maximum landscape slope within the site assessment area varied from one (1) and eleven
(11) degrees (Refer to Map 8).


6.1.3     FIRE WEATHER SEVERITY


In addition to vegetation fuel loads and slope, fire behaviour and intensity is influenced by
a range of weather variables such as wind speed, relative humidity, temperature and
atmospheric conditions, as well preceding drought conditions7.

These variables are summarised as an index value which can be used by proxy to estimate
and predict fire behaviour: Fire Weather Severity (FWS). The McArthur Forest Fire Danger
Index (FFDI) (McArthur 1967) is the most widely used proxy of fire weather severity in
Australia and is used for both bushfire hazard assessment, emergency management and in
regulations such as in AS 3959:2018 Construction of buildings in bushfire-prone areas.
Unlike AS 3959:2018, which adopts a single FFDI for all of Queensland (40), fire weather
conditions vary spatially according to temperature, wind, relative humidity and
precipitation. Although FWS is equivalent to the Forest Fire Danger Index (FFDI) defined
in AS 3959:2018; spatially explicit FWS values for Queensland have been calibrated by
Leonard et al. (2014) based on a gridded prediction of the FFDI from long term spatial
weather products produced by the Australian Bureau of Meteorology. Adopted FWS
values reflect a 1:20 year or 5% annual exceedance probability (AEP) weather event.

Climate change projections suggest that the likelihood, intensity and extent of bushfires
are likely to increase, together with longer, hotter and drier fire seasons (Bureau of
Meteorology 2019). The gridded fire weather severity values for Queensland have been
adjusted to reflect the expected climate in 2050 using the Intergovernmental Panel on
Climate Change A1FI climate scenario8 (Queensland Fire and Emergency Services 2019).

The fire weather severity used for the purpose of calculating fireline intensity was based
on 1 in 20-year weather conditions (i.e. 5% annual exceedance probability) to reflect the
severity of fires and events suited to mitigation through land use planning in Queensland
and was based on advice from the Queensland Fire and Emergency Services.

An FFDI of 48 was adopted based on the 5% AEP event as per Leonard et al. (2014)
(Refer to Map 9).




7 Days since last rainfall.


8 The SRES A1FI scenario is most similar to the current RCP 8.5 scenario.




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