what are the main causes of bushfires (2)

What Are The Main Causes Of Bushfires?

Bushfires and grassfires are common throughout Australia. Grassfires are fast-moving, passing five to ten seconds and smouldering for minutes. They have a low to medium intensity and primarily damage crops, livestock and farming infrastructure, such as fences. Bushfires are generally slower-moving but have a higher heat output. This means they pass in two to five minutes, but they can smoulder for days. Fire in the crown of the tree canopy can move rapidly.

Bushfires are an intrinsic part of Australia's environment. Natural ecosystems have evolved with fire, and the landscape, along with its biological diversity, has been shaped by both historical and recent fires. Many of Australia's native plants are fire-prone and combustible, while numerous species depend on fire to regenerate. In addition, indigenous Australians have long used fire as a land management tool. It continues to be used to clear land for agricultural purposes and protect properties from intense, uncontrolled fires. Historically, bushfires have caused loss of life and significant property damage. While naturally occurring bushfires cannot be averted, their consequences can be minimised by implementing mitigation strategies and reducing the potential impact on the most vulnerable areas.

Why Do Bushfires Occur?

Bushfires can be started by natural causes, such as lightning strikes or by people (accidentally or on purpose). In addition, weather and fuel conditions play a part in bushfires. Materials such as leaf litter, bark, small branches and twigs, grasses and shrubs can fuel bushfires. Dry fuel is more likely to catch fire and burn easily; damp fuel may not burn. The type of fuel that is available to burn, how much of it is, and how dry or moist it will influence bushfire conditions. Hot, dry and windy weather can contribute to fire danger. Specifically, weather-related factors that contribute to an increased risk of bushfire danger include:

  • High temperatures
  • Low humidity
  • Little recent rain
  • Abundant dry vegetation
  • Strong winds
  • Thunderstorms

FAQs About The Causes Of Bushfires

Between 26 December 2019 and 1 January 2020, due to a lightning strike, a fire tore through 40,000 hectares (99,000 acres) of land in Stirling Range National Park in the southwest of the state, burning more than half of the park.

Lessening the presence of fuels in forests or grassland areas; • slowing down and sometimes ceasing the spread of bushfires; and • providing easier access routes for firefighters to reach and extinguish fires. Fuel reduction is paramount to bushfire minimisation.

1.65 The Department for Environment and Heritage (DEH) is responsible for bushfires across South Australia's parks and reserve system and crown land under their control.

Thirty-three people lost their lives during the bushfire emergency, including volunteer firefighters. The impact of the bushfires on Australia's biodiversity was significant. The Government has committed an initial $50 million to protect wildlife and support longer-term protection and restoration efforts.

Bushfires can be started by natural causes, such as lightning strikes or by people (accidentally or on purpose). In addition, weather and fuel conditions play a part in bushfires. Materials such as leaf litter, bark, small branches and twigs, grasses and shrubs can fuel bushfires.

Bush fire hazards are any materials that can fuel a fire, such as a leaf litter, grass, garden mulch and woodpiles. They can also be made up of solid combustibles or flammable liquids and gases such as petrol, kerosene, alcohol, LPG, natural gas, and acetylene.

The burning fuel will produce only water and carbon dioxide (no smoke or other products). The burning fuel will produce only water and carbon dioxide (no smoke or other products). The flame is typically blue.

Bushfires are the result of a combination of weather and vegetation (which acts as a fuel for the fire), together with a way for the fire to begin – most commonly due to a lightning strike and sometimes human influences (mostly accidental such as the use of machinery which produces a spark). Depending on weather conditions, embers can be transported by wind from one location to another, causing new fires or spotting.

When they are large enough, bushfires can generate local weather impacts such as lightning, tornadoes and firestorms, which, in turn, can impact fire behaviour. The terrain of an area (or the landscape) contributes to the spread and management of a bushfire. Fires burn faster uphill and can build in intensity and speed. Fires that start in remote, rough or hilly terrain can be difficult to fight.

The basic factors that determine whether a bushfire will occur include fuel, oxygen, and an ignition source. The fire intensity and speed at which a bushfire spreads will depend on ambient temperature, fuel load, fuel moisture, wind speed and slope angle.

Fuel Moisture

Dry fuel will burn quickly, but damp or wet fuel may not burn at all. Consequently, the time since rainfall and the amount of rain received is an important consideration in assessing bushfire danger. Often a measure of the drought factor, or moisture deficit, will be used to indicate extreme bushfire weather conditions.

Wind Speed

Wind acts to drive a fire by blowing the flames into fresh fuel, bringing it to ignition point and providing a continuous supply of oxygen. Wind also promotes the rapid spread of fire by spotting, igniting new fires by burning embers lofted into the air by wind. Spotting can occur up to 30km downwind from the fire front.

There is a threshold wind speed of around 12 to 15km/h, which makes a significant difference in the behaviour of bushfires in the open. When wind speeds are below this threshold, fires with heavy fuel loads burn slowly. However, even a slight increase in wind speed above this threshold results in a significant increase in fire behaviour and advancement. The width of a fire front also influences the rate of spread, and a wind shift can immediately widen the forward edge of a fire.

Ambient Temperature

The higher the temperature, the more likely a fire will start or continue to burn. The fuel is closer to its ignition point at high temperatures, and pre-heated fuel loads burn faster.

Relative Humidity

Dry air promotes a greater intensity fire than moist air. In addition, plants become more explosive at low humidity because they release their moisture more easily.

Slope Angle

Fires pre-heat their fuel source through radiation and convection. As a result, fires accelerate when travelling uphill and decelerate travelling downhill. The steepness of the slope plays an important role in the rate of fire spread. The speed of a fire front advancing will double with every 10-degree increase in slope so that on a 20-degree slope, its speed of advance is four times greater than on the flat ground.

Ignition Source

what are the main causes of bushfires (3)

Bushfires can originate from human activity and natural causes, with lightning the predominant natural source, accounting for about half of all ignitions in Australia. Fires of human origin currently account for the remainder and are classified as accidental or deliberate. Fires lit deliberately can result from arson or be designed to achieve a beneficial outcome, but conditions have changed, resulting in the uncontrollable spread.

Unfortunately, deliberate and accidentally lit fires are more prevalent near populated areas and have a disproportionately higher risk of infrastructure impact. In addition, arsonists place people and property at serious and unnecessary risk, particularly when igniting fires on extreme fire weather days.

Where Do Bushfires Occur?

The Australian climate is generally hot, dry and prone to drought. As a result, some parts of Australia are prone to bushfires at any time of the year. The varied fire seasons reflect the continent's different weather patterns. For most of southern Australia, the danger period is summer and autumn. For New South Wales and southern Queensland, the peak risk usually occurs in spring and early summer. The Northern Territory experiences most of its fires in winter and spring.

Grassland fires frequently occur after good periods of rainfall, resulting in abundant growth that dries out in hot weather. Bushfires tend to occur when light and heavy fuel loads in Eucalypt forests have dried out, usually following periods of low rainfall.

The potential for extreme fire weather varies greatly throughout Australia, both in frequency and severity. However, a significant loss is possible when potential extreme fire weather is experienced close to populated areas. In terms of the total area burnt, the largest fires are in the Northern Territory and northern areas of Western Australia and Queensland. Most loss of life and economic damage occurs around the fringes of cities where homes are commonly near flammable vegetation.

Risks

Bushfires can cause serious property and infrastructure damage and lead to loss of life. The fire itself is only one element of the danger. Other impacts from bushfires include the effects of radiant heat and smoke.

  • Fire embers can spread many kilometres from the location of a large bushfire, causing smaller spot fires to break out.
  • Radiant heat can be felt more than 100m away from a large bushfire and has the potential to melt or fracture objects, including parts of cars, glass windows, etc.

Toxic fumes and heavy smoke produced from bushfires can impair vision, impact air quality, and create difficulties in breathing. In addition, due to the unpredictable nature of fast-moving fires, people are likely to be encouraged to evacuate from their homes as quickly as possible to ensure they can reach safety. Therefore, it is important to follow any local alerts and warnings.

Why Has This Fire Season Been So Significant?

Of the three factors that contribute to fire behaviour, two have played a major role in this bushfire season for Australia's eastern and southern states: weather and vegetation.

Weather

Weather relates to conditions over short periods. For example, the risk of bushfires starting or advancing out of control is highest when there is 'fire weather' – a combination of strong winds, low humidity and high temperatures. In 2019, southern and eastern Australia experienced record low rainfall and high temperatures, contributing to the increased frequency of fire weather days.

Vegetation

Vegetation, including trees, grasses, bushes and leaves, fuel a bushfire. The more abundant and drier the fuel, the more intense the fire will burn. Nationally-averaged rainfall was 40 per cent below average for the year, making 2019 Australia's driest year since records began in 1900. Many parts of southern and eastern Australia are in a drought and have been for multiple years, impacting both the rate of vegetation growth and its dryness. Fuel management, including hazard reduction burns, can reduce the likelihood of ignition and initial rates of spread in high-risk areas if carried out in an appropriately targeted manner. 

The Role Of Climate Change

Climate change doesn't cause fires directly but has caused an increase in the occurrence of extreme fire weather and the length of the fire season across large parts of Australia since the 1950s. In addition to 2019 being the driest year since records began in 1900, Australia's warmest year. In 2019 the annual mean temperature was 1.52 °C above average1. The impact of climate change has led to longer, more intense fire seasons and an increase in the average number of elevated fire weather days, as measured by the Forest Fire Danger Index (FFDI). Last year saw the highest annual accumulated FFDI on record.

Living With Bushfires And The Role Of Science

Although bushfires are a natural part of life in Australia, preparing for and managing bushfires is critical to minimise the risk and potential damage of bushfires each season. Fire prevention measures include:

  • Fuel management (including hazard reduction burns) before the fire season
  • Ignition prevention (including total fire bans) before the onset of a bad fire day
  • Use fire suppression tools when a bushfire breaks, including active fire-fighting with water and fire retardants, back burning, and land clearing for fire breaks.

In the medium to longer term, where and how we live and organise our communities and how and where we build our houses also play an important part in preparing and responding to bushfire threats. Our national science effort remains to provide the information necessary to improve our overall bushfire understanding and preparation. Australian researchers produce some of the world's best climate, weather, fire and disaster research; and work closely with operational agencies, governments and communities to better prepare for, respond and recover from these events.

Strategy For Fire Management Expansion.

what are the main causes of bushfires (1)

National Parks and Wildlife Service firefighters and staff plan hazard reduction activities. To do this, they need to understand fire behaviour in the NSW bush and stay up to date with current policies and procedures. We have developed the Living with Fire in NSW National Parks strategy, providing a state-wide fire management approach. The national strategy is detailed in the National Bushfire Management Policy Statement for Forests and Rangelands, which describes how the sustainable management of fire across the Australian landscape is coordinated. Fire management practices are responsive to change. We have identified key challenges and future trends in fire management.

Key challenges for fire management include:

  • more people living in regional NSW near bushfire prone areas
  • the ageing population of residents and firefighters
  • the increasing cost of fire suppression
  • the increase in size and distribution of protected areas
  • the increase in average temperatures, decrease in average rainfall and the subsequent increase in severe fires
  • technological advances such as management information systems and fire and weather behaviour modelling.

Key trends in fire management include:

  • the relationship between global climate and weather systems and the number of fires and areas burnt in parks
  • the slight downward trend in the annual average size of fires in parks and reserves over the last 35 years due to improved bushfire detection and suppression
  • various causes and origins of fires in parks, and the contribution of hazard reduction and unplanned fires to total area burnt.

Conclusion

Bushfires are a natural part of the Australian landscape. Many of our plants need bushfires to regenerate, and many have adapted to the harsh conditions our climate delivers. However, with such a vast country, just as the landscape changes from place to place, so does the bushfire risk and the timing of the bushfire seasons.

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