Which homes will survive this bushfire season?
AFTER the early onset of the 2013-14 bushfire season, it is worth reviewing which homes are more likely to be left standing when the fires inevitably return.
One of the most important factors to note is that most house losses during bushfires in Australia have occurred within 100 metres of bushland - and virtually all losses within 700 metres of bushland. So the measures discussed here relate principally to houses close to bushland areas.
Clearing nearby hazards
The single most effective hazard reduction measure during the 2009 Black Saturday bushfires was clearing native trees and shrubs within about 40 metres of homes. A low cover of trees and shrubs in this zone will act to reduce radiant heat and the volume of embers showering a house and also creates an area where adequately equipped individuals are more likely to successfully defend a house.
The type of garden around a home is also important. Houses among remnant native bushland are at greater risk than houses surrounded by a planted garden. Some research suggests that this is because of the amount of fine fuel (such as dead leaves) at ground level, since planted gardens tend to be more manicured.
Preliminary results from a study we are doing suggest that there may be some protection afforded by gardens that are regularly watered.
The upwind distance from houses to intact bushland is another crucial variable. Houses closer to intact bushland are at greater risk.
There is additional risk for houses close to bushland that is publicly managed, such as a state forest or national park. The reason for this is unclear, but may be because this bushland occurs as large, continuous patches and often on steeper terrain. There is no evidence that national parks present greater risk than other types of public land, such as state-owned land that is logged.
Will burn-offs save my home?
Despite a focus on hazard reduction burning by many commentators after bushfires in Australia, we found it was not as effective as the measures listed above.
On Black Saturday, there was only a moderate reduction in risk to houses from hazard reduction burning, but only where it was undertaken close to houses and within five years.
There is evidence that hazard reduction burning helps limit the spread of bushfires that burn in moderate weather, but has less effect on bushfires burning during extreme and catastrophic conditions.
Yet most houses are destroyed during bushfires burning in extreme and catastrophic fire weather. For example, the small town of Marysville in Victoria was devastated on Black Saturday, despite a ring of previous hazard reduction burning.
Hazard reduction burning is also a challenge for fire management agencies. While the effect is short-lived, lasting less than five years, there are other factors to manage, including the effects from the smoke on people's health, that the window of time for hazard reduction burning in any year can be short, and the ever-present risk of burn-offs getting out of control, such as in Margaret River in Western Australia two years ago, when 34 houses were destroyed.
Thus, home owners should not see hazard reduction burning as the single solution that will protect their houses from bushfires.
It's impossible to save every house
The combination of all of the above actions - clearing close to houses, maintaining neat gardens, being further from bushland and regular hazard reduction burning close to houses - can substantially reduce house losses during bushfires in Australia.
However, it is not feasible to apply all of these measures at every house.
If you live close to bushland you cannot simply move your house. Peri-urban areas, like the Blue Mountains in NSW, attract many people because of the bushland and its associated wildlife, so broad-scale clearing is unlikely to be tolerated by these communities. Hazard reduction burning near every house is also not feasible.
Thus, only some of these risk factors will ever be addressed at most houses in bushland areas.
Further, there are other factors that influence whether a house will survive a bushfire such as building design, whether a fire brigade is in attendance and local weather conditions. For example, bushfires can generate convective winds that are strong enough to rip off the roof of a house. A house is virtually impossible to defend if this happens.
We must accept that houses will continue to be destroyed by bushfires in Australia.
Strategies such as safer places and early evacuations must therefore remain under strong consideration for people living in bushfire-prone areas.
And we must carefully consider where new houses should be built. House losses and unnecessary deaths will continue to increase in Australia if we keep building homes in bushfire-prone areas.