3. Bushfire Hazard Assessment for Development Applications

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Following the development of the State Planning Policy “SPP1/03 -  Mitigating the Adverse Impacts of Flood, Bushfire and Landslide” in 2003, all Qld planning schemes were required to include the identification of affected land (by way of a natural hazards map or a specific flood or bushfire or landslide map and a Planning Scheme Policy) which provided a methodology for assessment and reporting the constraint. Because SPP1/03 was developed under the (then) Integrated Planning Act 1997 and this was a performance based assessment, the planning scheme was to also provide a code which outlined a Performance outcome and an acceptable outcome or solution which development being proposed in a development application were to meet.

While many Planning Schemes prepared under the Integrated Planning Act 1997 introduced natural hazards, many did not.  Prior to the introduction of the State Planning Policy SPP1/03, the State Government (through the Queensland Fire and Rescue Service) had developed local government area wide bushfire risk maps which mapped at a very broad scale, areas of bushfire hazard and bushfire risk and all other areas which were not mapped as one of those two criteria were deemed to be areas of low bushfire hazard.

Following the introduction of the State Planning Policy SPP1/03, a methodology was introduced for assessing bushfire hazards using three key elements, vegetation, slope and aspect.  Vegetation types based on the general structural characteristics were described and a score between 0 and 10 was used.  With respect to slope and aspect, a score of 0 to 5 was used.  Each element was determined individually and then the sum of the three individual scores were calculated to determine a total bushfire hazard score.

A score less than 5.5 was determined to be low bushfire hazard, a score between 6 and 12.5 was an area of Medium bushfire severity and a score greater than 13 placed the area into a High bushfire severity class.

The methodology contained in State Planning Policy SPP1/03 became the standard for assessing and determining the bushfire hazard severity throughout Queensland and was used by many Local Governments within their Planning Schemes that were prepared under the Integrated Planning Act 1997 to prepare a bushfire hazard map within their local government area.

SPP1/03 was replaced in 2014 when the State Government introduced the single State Planning Policy of which Natural Hazards became one of a number of issues, referred to as State interests.  Along with the new single State Planning Policy, the State Government commissioned the Commonwealth Science, Industry and Research Organisation (CSIRO) bushfire scientists to develop a new bushfire hazard mapping methodology.  This new methodology, referred to as the Fireline Intensity Model, used a set of different metrics and terminologies to determine the status of the “Potential fireline intensity” or “potential Bushfire Hazard Class’.

These metrics included,

·        Vegetation, which was described as the Vegetation Hazard Class and while it initially used Regional ecosystems to describe the vegetation, this was changed to Broad Vegetation groups which is still currently in use.  Additional Vegetation hazard classes were also introduced to describe urban and rural vegetation which were not considered to be a broad vegetation group by the Queensland Herbarium.  A practitioner is to determine the VHC within an area which a development application is being made.

·        Potential fuel load.  Fuel loads were attributed to each of the vegetation hazard classes. There is still some discussion as to the accuracy of some of the potential fuel loads attributed to many of the vegetation hazard classes.  The methodology does not permit site-based assessments of the fuel loads to be used but has attributed each VHC with its own potential fuel load within the fireline intensity model.

·        Fire weather severity.  This is a value based on the McArthur methodology for calculating the FFDI or FDI (Forest Fire Danger Index), which is a measurement of the likelihood of a fire commencing in a particular site, given the rainfall history and climatic conditions at the time.  FFDI scores range from 1 to 100 with 1 being no chance of a fire commencing to 100 which is an extreme chance of a fire commencing.  The methodology purports to have used detailed Bureau of Meteorology climate data to determine the FFDI throughout the State based on a 1 in 20 year or 5% annual exceedance probability, that is 5% chance of occurring any year was adopted.  A practitioner is required to use the State derived Potential fire severity weather value for the area being assessed.

·        Maximum landscape slope.  A score is attributed based on the maximum potential slope within an area.  The practitioner can use site-based slope values within the fireline intensity model.

·        The model therefore determines the Fireline intensity value and depending on the fireline or bushfire intensity value, the area is placed into a potential hazard class which has the following values

o   NBPA – not a bushfire prone area = <4,000 kW/m

o   Medium bushfire hazard class = >4,000kW/m - <20,000kW/m

o   High bushfire hazard class = >20,000kW/m - <40,000kW/m

o   Very High bushfire hazard class >40,000kW/m.

·        In addition to the bushfire hazard class mapping, the State Planning Policy also requires a 100-metre-wide “Potential impact buffer” be placed around any area of Medium, High and/or Very high bushfire hazard class.

Therefore, nearly all of the current Local government planning schemes now contain a map which has been developed under the bushfire hazard methodology developed by the CSIRO.  Brisbane City is the one notable exception which still has a bushfire overlay map which was developed generally based on the SPP1/03 methodology and instead of using the SPP1/03 vegetation types, Brisbane City Council uses their own vegetation mapping.

It is also important to note that the State Planning Policy bushfire hazard mapping has gone through several iterations and many of the planning scheme maps contain an earlier iteration which in some areas is different from the latest iteration.

It is also important to note that the State Planning Policy bushfire hazard mapping, including the Bushfire Overlay Map in the Brisbane City Plan (2014) are trigger maps (to determine the category of assessment and for assessment against the Overlay code), if a development is within a bushfire hazard class or within a potential impact buffer.

Therefore, if a development is located within a bushfire hazard class area including the potential impact buffer, there are two choices for an applicant for development to proceed,

1.     Accept the bushfire hazard overlay mapping and undertake the development (in terms of layout and configuration) based on that mapping, of course amongst all other site constraints, and design in setbacks accordingly; or

2.     Undertake a site-specific bushfire hazard assessment and prepare a bushfire hazard report based on the site-specific characteristics and undertake the design and configuration of the development proposal based on the informed site specific bushfire hazard investigation.

I would note that while the latest State Planning Policy, bushfire hazard mapping is better than the earlier iterations at a broad level, it still is not entirely accurate at individual property level and as such a site-based assessment can generally provide better information to support proposed development, than relying on the existing mapping in the planning scheme.

In addition to the bushfire hazard mapping, the State Planning Policy introduced terms such as acceptable risk and tolerable risk, and these (or the alternative ‘un-acceptable’ risk) have made their way into planning schemes.  These terms have the capacity to draw into development assessment benchmarks used in building assessment and these are found within the Australian Standard – Construction of buildings in bushfire prone areas – AS3959-2009.

In addition to specific site characteristics, other issues such as existing land management practices, the status of the understorey in terms of species and density and existence of established firebreaks and fire trails should also be noted.  In many areas throughout South-east Queensland, fire has not been part of that landscape for many years and this has allowed for tree canopies to close, the understorey to change in terms of density and species and these changes may in fact result in a decrease of the potential for that vegetation patch to become involved in a bushfire event and if it were, for that fire to remain within the understorey and not progress into the canopy.

Likewise, in areas where paperbark tea tree (Melaleuca spp.) have recolonised a retired pasture area, the potential bushfire hazard class may have in fact increased.

Bushfire consideration should also be given to proposed landscape planning, particularly in areas where there is an acknowledged bushfire hazard.  Landscaping should not allow for any significant connectivity between an area of bushfire hazard future structures.  The use of less flammable plant species can in some cases assist in managing the flammability of a landscaped area and provide a “green” firebreak between hazardous vegetation and structures.

And finally, as mentioned above, the Australian Standard, Construction in the Bushfire Prone Area – AS3959 is being referred to as a mechanism to reach an acceptable risk level by complying with the Standard.  It is important to note that there is clear demarcation between a development approval making conditions that are within the area of building assessment and within the responsibility of a building certifier.  This demarcation is specified within the Sustainable Planning Act 2009 and the Planning Act 2016, the Building Act 1975 s31 and the State Planning Policy – State Interests Guidelines (Natural Hazards, Risk and Resilience).

However, while the demarcation is there, the use of a building standard, i.e. a Bushfire Attack level (BAL), is being used as a solution to meet a performance outcome by way of an alternative solution.  It appears that different Local Governments accept this as an alternative solution or at least the setbacks which are required to attain a lower BAL level, such as BAL12.5 or BAL19 when a setback is provided in a planning scheme.