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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.

CSIRO | Hazard Reduction Burning Transcripts

1st October 2021 DESCRIPTION: An animated video.

A family of three stand huddled together outside their home under a dark, smoky sky. A bushfire burns on a hill in the distance. In the centre of the screen is a fire risk chart, featuring three coloured segments: green, orange and red. An arrow starts in the orange section, then moves into the red.

SPEAKER: How can we reduce the growing severity and increased threat of bushfires?

DESCRIPTION: A diagram appears on screen consisting of three segments – each depicting a colourful, outdoor scene – which together form a triangle. Text at each apex: Terrain, Weather, and Fuel. The terrain and weather segments are greyed out, highlighting the fuel segment. This scene depicts fallen sticks scattered around the base of a tree. A house sits amongst tall grass in the background.

SPEAKER: Of the 3 factors that drive fire behaviour, fuel is the only one we can influence.

DESCRIPTION: As the two other segments disappear, a fire risk chart appears beside the highlighted scene. The arrow on the chart goes from red to green as the dead wood and tall grass all disappear.

SPEAKER: By reducing the availability of the fuel that feeds a bushfire we can reduce its intensity, hazard, and impact.

DESCRIPTION: Text on screen: Hazard Reduction Burning. A series of icons appear in a spinning circle around the text. They depict: a warning sign, a red cross, a green tick, and a question mark.

SPEAKER: That’s where hazard reduction burning can help, but its success is influenced by many factors.

DESCRIPTION: In the bush, two firefighters light small, controlled fires amongst tall dead grass and dried sticks.

SPEAKER: Hazard reduction is deliberate, controlled burning, designed to reduce fuel availability.

DESCRIPTION: A map of Australia. Earth-coloured bands cover the country. Four seasonal charts are arranged over four regions on the map. In both NSW and south Queensland, and Western Australia, summer and spring are marked red, while autumn and winter are marked green. In south-east Australian, winter and spring are marked green while summer and autumn are marked red. In northern Australia, summer and autumn are marked green, while winter and spring are marked red. Green ticks appear above all the seasons marked green.

SPEAKER: To avoid increasing the risk of uncontrolled fire, it can only be done under certain conditions, before or after bushfire season depending on location and conditions.

DESCRIPTION: Four labelled tableaus appear on screen, each depicting a weather condition. A gauge at the bottom of each section shows the prescribed range. From left to right, the depicted conditions are wind speed, temperature, humidity, and rainfall.

SPEAKER: Wind speed, temperature, humidity, and rainfall need to be within certain parameters.

DESCRIPTION: A farmer stands amongst tall grass in a field. A cow grazes beside him, as bees buzz around a nearby apiary. Thick, dark smoke drifts through the sky in the distance as more smoke eventually covers the farm. A gauge on screen indicates diminishing air quality. The farmer frowns as the cow looks up.

SPEAKER: The effects of burning, such as smoke, must not affect local communities, industries, and ecosystems.

DESCRIPTION: Three firefighters stand in a V-formation in front of a fire truck, parked on a road surrounded by bushes. A map is superimposed over the background. Hazard area indicators appear on the map.

SPEAKER: It needs well equipped and experienced professionals with clear local fuel reduction objectives in mind.

DESCRIPTION: The hazard area indicators disappear as the map takes full screen. Fire risk charts appear on the map, all indicating different levels of risk.

SPEAKER: Care must be taken for each local ecosystem’s tolerance for burning.

DESCRIPTION: A fire truck speeds toward a raging fire. On the map, an arrow, indicating the truck, inches toward another marker, indicating the fire.

SPEAKER: Effective hazard reduction burning increases the ability of firefighters to manage bushfires when they do happen.

DESCRIPTION: Three scenes appear on screen. In the first, a fire rapidly spreads along a hill line, viewed from a farm. Text: slower spread. In the second, a fire rages in a heavily wooded forest area, under a dark orange sky.

Text: reduced intensity. In the third, shooting embers from a distant fire rain over trees, grass, and a building, which all catch alight. Text: less fire spotting.

SPEAKER: It slows the spread of new fires, reduces their intensity and the potential for fire spotting.

DESCRIPTION: Two firefighters douse a flame in the bush. A calendar appears, with numerous dates each marked with a tick. A clock, with a portion highlighted in blue, appears beside the calendar. A helicopter dumps water over the fire.

SPEAKER: This increases the window of opportunity and range of conditions in which firefighters can reach and safely suppress new fires before they become uncontrollable.

DESCRIPTION: Fire indicators appear on a map of Australia.

SPEAKER: Bushfires are a natural part of the Australian environment.

DESCRIPTION: Two people in white lab coats appear, as icons depicting data connected to various regions of the map. Two firefighters appear on the other side of the map.

SPEAKER: Better understanding their complex science and impacts, and the effects of hazard reduction burning, including its strengths and its limitations, can significantly reduce the risk of their potentially devastating impacts.

DESCRIPTION: A family of three appears in the centre of the screen. The scene fades away. The CSIRO and AFAC logos appear on a white background, above the text: Learn more at

SPEAKER: Learn more at

Hazard reduction burning explained

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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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