How do fires start?
The 2 leading causes of fire starting in NSW parks are:
- lightning – 38%
- arson or suspicious causes – 18%.
All fires need oxygen, heat and fuel to burn. How quickly a fire spreads and how intensely a fire burns depends on the type of fuel, the topography and the weather (mostly wind and temperature).
How do fires burn?
Bushfires occur often in south-eastern Australia where the weather is often hot and dry. Fire spreads by a process called heat transfer. This is when the material immediately next to a fire is preheated to the point where it gets hot enough to ignite.
Fire burns more quickly travelling uphill than downhill. The steeper the slope, the faster the fire will spread.
The aspect of the landscape, or the direction it faces, can also affect how fires burn. The aspect influences the type of plants that grows there and the level of moisture it contains. In New South Wales, west-facing slopes are the hottest and driest. The vegetation is more flammable, but the plants are also more fire tolerant. South-facing slopes are usually cooler and wetter with less flammable vegetation. However, these plants are less fire tolerant and fires in these areas can be devastating.
The amount of flammable material in a park is referred to as the fuel load. How much fuel builds up in a given area depends on how much the local vegetation 'sheds' dead fine fuel litter and how quickly it rots.
We measure the amount of fuel available to burn to determine the overall fuel hazard in our parks. The greater the fuel load, the higher risk of bushfire. The overall fuel hazard is rated from low to moderate, high, very high and extreme.
The overall fuel hazard is measured by assessing the hazard posed by the:
- type of bark on trees
- amount of ‘elevated’ fuel such as grasses, ferns and shrubs
- amount of fine fuel on the surface of the ground.
Research into fuel accumulation and rotting rates of different plant communities is used to develop fuel accumulation models. Fuel accumulation models are used when planning hazard reduction burns. We invest in research and development to help better manage bushfire risk and conserve biodiversity.
Wind and temperature have a major influence on fire behaviour.
Hot temperatures speed up the preheating of fuel and heat transfer, and allow a fire to spread more quickly.
Wind also speeds up the process of heat transfer by pushing flames and heat sideways to preheat unburnt areas. Wind can change the direction of a fire and turn the flank or side of a fire (lower intensity) into a fire front or the head of a fire (highest intensity).
Fire Danger Ratings for New South Wales are based on predicted conditions such as temperature, humidity, wind and dryness of the landscape. The Fire Danger Rating gives an indication of the consequences of a fire if one were to start.
Three types of bushfires occur in NSW parks: ground fires, surface fires and crown fires. One, two or all of these types of fire may make up a fire event.
A ground fire can occur in any conditions and is where peat, coal, tree roots or other materials ignite and burn under the ground. Ground fires can burn through to the surface and become surface fires.
Surface fires are low to high intensity fires that burn on the surface of the ground. The tree canopy may be scorched but does not burn to the extent that it will carry a fire.
A crown fire occurs during fires of extreme intensity. A crown fire is when fire burns and spreads through the crown or canopy of trees. The influence of wind is greater in the tree canopy. When the tree canopy is interconnected or continuous, a fire can spread incredibly quickly.
Responding to bushfires burning in parks
- Of the fires that start in parks, 90% are contained in parks.
- In 2015–16, the NPWS Remote Area Response Team (RART) responded to 100% of remote bushfires within 30 minutes of detection.
- In 2015–16, NPWS treated 203,800 hectares of land in hazard reduction activities, exceeding the targets of the Enhanced Bushfire Management Program.
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, which provides a state-wide approach to fire management.
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 New South Wales 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 area burnt in parks
- the slight downward trend in 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 burning and unplanned fires to total area burnt.
The following resources help us to best manage fire in NSW national parks:
- coordinated bushfire management strategies, policies and procedures
- access to more than 1,200 trained firefighters; variations to the number of staff available at any given time can occur as staff undertake the ongoing necessary accreditations required to safely undertake fire management activities
- a well-maintained fleet of NPWS firefighting vehicles
- 5 aircraft and specially equipped helicopter fleet and crew.