A study into the 2009 Victorian bushfires, which were the worst in Australian history, claiming 173 lives and incurring damages in excess of $4 billion, has revealed the need to rethink bushfire risk strategies.
Using statistical modelling, researchers at the University of Wollongong (UOW) studied a sample of 3500 houses affected by the Victorian bushfires of February 7 2009 to explore how the extent of forest and crown fire around houses affected the likelihood that they would be destroyed.
They found that houses with a large proportion of forest within 1km were at risk even if the trees were not near the house during crown fires, which occur when strong winds and large amounts of dry fuel allow the fire to jump from one tree top to the next at great speed and intensity.
“This means that embers coming out of the forest were more important than radiant heat from nearby patches of trees,” co-author of the study (published in PLUS ONE), Dr Owen Price, said.
This 1km risk zone is in stark contrast to the current zones stipulated by Australian fire management authorities, which vary according to jurisdiction from 25-500m.
“The zone of 1 km around houses is very large and requires a rethink of bushfire risk strategies,” Dr Price, said.
“This might include increasing the setbacks between houses and forest in new developments.”
Dr Price, a senior research fellow at the UOW Centre for Environmental Risk Management of Bushfires, said the study also found that houses were more likely to burn if there were other houses nearby (meaning house to house transmission of fire was occurring).
“Houses were more likely to be destroyed if there were other houses within 50m and if they were on a slope,” he said.
Dr Price said that since the Centre’s previous work showed that hazard reduction burning had little effect during catastrophic fire conditions, residents who live surrounded by forest should look to fireproof their houses.
“Since our previous work has found that time-since-fire did not reduce the likelihood of crown fire in catastrophic fire weather conditions, prescribed burning would provide only minor risk reduction in these fires. Under more benign weather prescribed burning is more effective and the risk zone is probably less than 1 km.
“Because the main threats seem to be from embers and house to house transmission, hardening houses to fire is another obvious way that risk could be reduced.”
Source: University of Wollongong