What Is Bushfire Risk?
Bushfire risk is the likelihood of a fire starting, spreading and impacting on people, property and the environment – the things we care about most.
Victoria is particularly susceptible to large, intense bushfires which can spread up to 30 km or more across landscapes. This is due to Victoria's terrain, naturally flammable vegetation and frequent exposure to hot, dry, windy weather.
Factors which affect bushfire risk include the type and condition of fuels, weather, topography, the location of people and assets, as well as our ability to prevent fires from igniting and suppress them once they have started. Reducing the impacts of bushfires is challenging because we don't know exactly when and where they will occur.
However we can model how bushfires start and spread in the landscape with simulation software, Phoenix RapidFire, developed specifically for Victoria. Phoenix RapidFire uses information about weather, topography, vegetation and fire history, to simulate and predict the spread and impact of bushfires and help us understand bushfire behaviour – including flame height, ember density, spotting distance, convection column strength and intensity.
Using these simulations we can understand how bushfires are likely to behave, and how assets and values might be impacted by bushfires.
© Paul Hitch
Our Changing Risk
Victoria's bushfire risk profile tells a story of how bushfire risk changes over time, based on bushfire history and our fuel management activities.
In 2002, bushfire risk in Victoria was almost 90 percent. Following a decade of drought and fire which included the 1.5 million hectare Alpine fires in 2002-2003, the 1.0 million hectare Great Divide fires in 2006-07 and the 0.5 million hectare 2009 Black Saturday fires, bushfire risk fell to below 60 percent in 2010. With the recovery of our forests and parks from the impacts of these fires, and as fuel loads increase, bushfire risk has risen. It is now at 65 percent. Without effective intervention, it is likely to return to 2002 levels (almost 90%) by 2020.
We use this information to predict how risk will change as a result of our future planned burning and compare the effectiveness of different bushfire management strategies.
How We Measure Residual Risk
Using Phoenix RapidFire we simulate over 9,000 bushfires across Victoria under conditions of highest fuel in the landscape.
We estimate the average impacts on life and property based on these simulations.
We then simulate a second set of bushfires, under conditions which include planned burning and earlier bushfires in the landscape, and estimate the reduced impact on properties.
The impacts on life and property that remain after planned burning and bushfires, we call the 'residual risk'.
If residual risk is 100 per cent – there has been no fire in the landscape and no fuel reduced and we are at maximum risk where fires will spread and impact. If residual risk is at 70 per cent – the impacts to life and property will be reduced by about a third
Read more about how we are measuring bushfire risk in Victoria.
For fuel management on public land, the government will set a state wide target to maintain bushfire risk at, or below, 70 per cent of Victoria’s maximum bushfire risk. Based on the current assessment of risk, this will involve treating between 225,000 and 275,000 hectares in 2016-17. Where and how much land needs to be treated to keep bushfire risk at 70% will vary each year based on fire history, fuel loads and climate.
Managing Fuel Loads In Both Remote Places And Close To Towns
Under our integrated, risk-based approach, fuel management such as planned burning will be conducted in all parts of the landscape – around towns and assets and in the back country.
Modelling shows that we can significantly reduce risk through fuel management in remote areas. Knowing where fires are likely to start means we can reduce fuel loads and stop small fires from building momentum and spreading. This stops them from becoming major bushfires and gives our fire agencies a greater opportunity to control them before they affect our communities.
The maps below show the starting locations of over 9,000 Phoenix RapidFire simulated bushfires and the estimated number of properties impacted by each simulated bushfire. The maps below show simulated bushfires under a maximum risk scenario (where fuels in the landscape are at the highest possible level) and for the year 2015 (where fuels have been reduced by bushfires and fuel management).
Legend - Modelled property impact
Risk Beyond Life And Property - Other Assets And Values
It is important to understand the impacts of bushfires to not only life and property, but to infrastructure, the environment, businesses and communities. Many people and industries – including asthma sufferers, grape growers and bee keepers – and many native plants and animals are vulnerable to bushfires and can be affected by planned burning.
We are developing ways to measure the costs and benefits of different bushfire risk reduction strategies on the things we value – both how effective they are at reducing risk, and their impacts.
This includes impacts on lives, property, critical and community infrastructure, businesses, cultural heritage, ecological resilience, biodiversity including threatened species, and ecosystem services, such as water, landscape amenity, carbon and climate moderation including smoke. Understanding these impacts is important to ensure our bushfire management actions keep Victorians safe without creating unnecessary impacts on the things we value most.
Bushfire Risk Landscapes
We can measure bushfire risk for the whole of Victoria and at local landscape scales. Bushfire Risk Landscapes are geographical areas of Victoria that are grouped together because bushfires tend to behave in a similar way in those locations. There are seven landscapes across Victoria and we strategically plan for bushfire management in each landscape.
We need to manage each landscape differently so that our actions meet the unique needs of local communities and ecosystems.
Bushfire risk is not evenly distributed across all seven risk landscapes. The amount of bushfire risk in a landscape is related to where communities and assets are located, the size of those communities, the types and arrangements of vegetation (fuel) and topography. Not all communities at highest risk from bushfires are located immediately adjacent to forests and other vegetation.
This map shows the proportion of Victoria's current bushfire risk located in each landscape and the residual risk. Some landscapes, such as Mallee and Murray Goulburn, have a low proportion of Victoria's bushfire risk but have high residual risk because most of the fuel load is on private land. In this case, planned burning on public land won't do a lot to reduce risk in these landscapes.
Proportion of Victoria's Total Bushfire Risk By Landscape
Alpine and Greater Gippsland - 11%, Alpine and North East - 6%, Barwon Otway - 20%, East Central - 35%, Mallee and Murray Goulburn - 4%, South Western 6%, West Central - 17%
Managing Risk Across The Landscape
Because bushfires burn on private and public land, land and fire agencies will work with you to deliver an integrated approach to fuel management.
Modelling shows that by only managing fuel on public land, bushfire risk is unlikely to get below about 40 percent. Achieving this level of risk reduction would also require a significant amount of fuel management – a level that would likely have major impacts on native plants and animals and would not be sustainable for our communities. That's why fuel management on public land needs to be integrated with management of private land, as well as other management strategies to reduce bushfire risk.
Beyond Fuel Management
No single strategy or action alone can manage bushfire risk. We must develop a multifaceted approach, using all the activities available to us.
Fuel management is just one strategy for reducing bushfire risk.
Planned burning is a key part of fuel management, but it also includes:
- slashing and mowing
- creating fuel breaks around towns and assets
- maintaining infrastructure like fire dams and lookout towers in our forests and parks
Beyond fuel management, our fire management activities include:
- preparing and positioning firefighters and aircraft across Victoria for rapid response to bushfires when they start
- building standards for new housing
- developing neighbourhood shelters
- issuing community warnings
- coordinating evacuations
Our land and fire agencies will work in partnership with local communities through these initiatives to best reduce risk in a particular landscape.