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By Ruth Dawkins 4 October 2021 6 min read

Extreme events such as bushfires are becoming more common in Australia. Image/Flickr

The how and why of hazard reduction burning

Australia’s unique climate and geography have always left us vulnerable to extreme weather events, but climate change is now exacerbating those conditions further.

We are experiencing bushfires that are more severe and more frequent, putting unprecedented stress on communities and response teams, and resulting in substantial social, environmental and economic costs.

In such challenging circumstances, we need to use a toolbox of approaches for risk reduction. One of those tools is hazard reduction burning, a technique that has an important role to play in fire management across Australia.

What is hazard reduction burning?

When bushfires occur, their behaviour is driven by three factors: weather conditions, terrain, and fuel. Of these three, the factor that we can have the most direct influence on is fuel – fine combustible vegetation and debris like dry grass, dead leaves, bark, and twigs.

Hazard reduction burning is the deliberate, controlled use of fire in the landscape undertaken during low-risk conditions to reduce the availability of the fuel that feeds a bushfire.  Hazard reduction burning is just one type of prescribed burning, which may be undertaken for various purposes. These purposes include removal of post-harvest forestry debris, site preparation and seedling regeneration, cultural reasons, ecological management or biodiversity habitat management. Each of these will also have some impact on reducing bushfire hazard, even though that is not their primary purpose.

Low-risk conditions typically occur in early spring and late autumn in southern Australia, when the fuel is dry enough to burn but we are not subject to the high temperatures, low fuel moistures and strong winds that would risk the fire getting out of control.

Used alongside other fire management approaches, hazard reduction burning can reduce the intensity, hazard, and impact of a bushfire, and in doing so reduce the potential for loss of life and property. Watch the video below for more explanation.

What can hazard reduction burning achieve in Australia?

According to Dr Andrew Sullivan, leader of CSIRO’s Bushfire Behaviour and Risks team, hazard reduction burning by itself is not a panacea.

"There’s no ‘solution’ to bushfires," says Dr Sullivan.

"Fire is an integral part of our land, essential to many of our ecosystems, so instead we need to employ multiple approaches that can help mitigate the threat without creating new problems. Hazard reduction burning is just one of a suite of tools that we use in fire management. But it significantly improves our ability to manage wildfires when they do occur."

When the weather conditions are extreme, our ability to manage fires becomes very limited and the effect of hazard reduction efforts decreases. But hazard reduction burning lengthens the window of opportunity for effective action when fires are controllable and increases the ability of emergency services to safely suppress a fire before it becomes uncontrollable.

Where hazard reduction burning has been carried out, we know that it slows the spread of fires, reduces their intensity, and lowers the potential for spot fires.

What are the complexities?

The success of hazard reduction burning is influenced by many different considerations, including economic, environmental, social and management.

The diversity of Australia’s landscape makes it difficult to reliably extrapolate and apply knowledge gained in one region to another.

The window of opportunity for conducting effective hazard reduction burns in the right conditions – taking into account wind speed, temperature, humidity and rainfall – varies from one part of the country to another and is decreasing as a result of climate change. Similarly, the type and amount of fuel and the subsequent effect of a burn on fuel hazard and any wildfire that may impact it varies with the prevailing conditions and location.

In order to conduct effective hazard reduction burning, we need practitioners who are not just well-equipped and experienced, but who also have extensive local knowledge. While it’s possible to share best practice, there is no one-size-fits-all solution that can be applied to the whole country.

The costs of hazard reduction burning as well as the benefits also need to be weighed. Even successful controlled burns can have significant impacts on surrounding communities and infrastructure – from individuals with respiratory illnesses to agricultural production and ecosystems.

"That’s especially true when you’re looking at how often a hazard reduction burn should be carried out to maintain a given level of hazard," says Dr Sullivan.

"The ideal return interval for effective hazard reduction may be at odds with the ideal return interval for the health of an ecosystem, so we have to consider the trade-offs. Is it better to have a planned burn, in which case we know there will be moderate impacts; or do we choose not to do a hazard reduction burn, but then run the risk of more extreme impacts from a wildfire that may or may not occur? There isn’t always a clear or easy answer so the decision will depend upon the specific ecosystem, situation and level of risk."

One of the challenges for fire managers is a lack of reliable models or case studies that focus specifically on quantifying the effect of hazard reduction burning on fuels and the effect of hazard-reduced fuel on wildfire behaviour under real-world conditions. Such studies – especially if they recognised the costs as well as the benefits - would support more informed decision making in this space.

Hazard reduction burns underway before summer bushfire season. Sydney, Australia - 17 October 2020. Image/Shutterstock

What is the intersection between hazard reduction burning and cultural burning carried out by Indigenous people?

Indigenous people in Australia have used fire to manage land for many thousands of years.

Cultural burning involves manipulating fire to create mosaic of burned patches across the landscape, with practices carefully tailored to protect designated features of the ecosystem. It generally takes place on a much smaller scale than a hazard reduction burn.

While cultural burning can achieve some level of hazard reduction, it’s often done for ecological or cultural purposes such as hunting, creating pathways, removing invasive species or Ceremony.

Although cultural burning is about more than just hazard reduction, it may still have a role to play in building resilience and increasing our efforts to mitigate risk from bushfire. In one recent project, CSIRO worked with Indigenous fire experts to design landscape burning partnerships, projects and activities across Australia. This led to two-way knowledge exchange and the incorporation of cultural burning practices into Western land management practices.

What work is CSIRO doing to inform hazard reduction burning practices?

CSIRO has been providing cutting-edge bushfire research for the last 70 years, enabling a broad range of stakeholders - from government agencies through to frontline firefighters and the general public – to make informed decisions about bushfire preparation, fire response and suppression, and disaster resilience.

Science and knowledge: educating communities and preparing for bushfire is a collaborative effort.

Specific work has included:

  • producing guides in specific fuel types for safe and effective hazard reduction burning for use by land managers
  • developing a smoke hazard prediction tool to help guide planned burning in sites with high value or vulnerability and to minimise public impact
  • developing a national bushfire hazard planning map to improve bushfire prevention and preparation
  • development and refinement of fire behaviour models for important vegetation types including eucalypt forest, croplands, mallee-heath and shrublands that aid understanding of effect of fuel management
  • design and construction of a next generation bushfire spread simulation framework called Spark that was recently selected by AFAC to be the basis of the next national operational bushfire simulator, and which can be used to quantify risk spatially to prioritise regions for hazard reduction and other fire management actions
  • training and aiding of national fire behaviour analysts who undertaken prediction of wildfires for early warning of the general public and suppression planning

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