The NSW National Parks and Wildlife Service (NPWS) undertakes ongoing research to better understand fire behaviour and improve fire management practices across NSW national parks.
How fires start
Only a small proportion of bushfire ignitions in New South Wales occur within national parks. The most common cause is lightning.
All fires need oxygen, heat and fuel to burn. How quickly a fire spreads and how intensely a fire burns depends on:
- the type and amount of fuel
- the shape of the land (topography)
- weather conditions, especially wind and temperature.
How fires burn
Bushfires are common in south-eastern Australia, where conditions are often hot and dry. They spread through heat transfer, where nearby material is heated until it ignites.
Fire behaviour is influenced by the landscape, particularly slope and aspect.
Slope
Fires travel faster uphill. The steeper the slope, the faster the uphill spread.
Aspect
Aspect refers to the direction a slope faces. West-facing slopes are hotter and drier, with more flammable vegetation. South-facing slopes are cooler and wetter, but vegetation is often less fire-tolerant.
Fuel load
The amount of flammable material is called the fuel load. This includes leaf litter, grasses, shrubs and bark. Fuel load builds up over time depending on how much vegetation accumulates and how quickly it breaks down.
We assess fuel to determine the overall fuel hazard, which ranges from low to moderate, high, very high and extreme.
The overall fuel hazard is based on:
- the type of bark on trees
- the amount of ‘elevated’ fuel such as grasses, ferns and shrubs
- the amount of fine fuel (for example, twigs and leaves) on the surface of the ground.
Fuel data and research help guide hazard reduction burns and other fire management activities.
Weather
Weather plays a major role in how fires behave, in particular temperature and wind. Hot conditions dry out fuel and allow fires to spread more quickly. Wind pushes heat and flames forward, increasing fire spread and causing it to change direction.
Fire danger ratings in New South Wales are based on predicted conditions such as temperature, humidity, wind and landscape dryness. They indicate how dangerous a fire could become if it starts.
Types of bushfires
Three main types of bushfires occur in NSW: ground fires, surface fires and crown fires. A bushfire may include one or more of these.
Ground fires
Ground fires burn beneath the surface in materials such as peat, coal or tree roots. These fires can smoulder for long periods and may re-emerge as surface fires.
Surface fires
Surface fires are low- to high-intensity fires that burn on the surface of the ground. They burn leaf litter, grasses and low vegetation and may scorch tree canopies.
Crown fires
Crown fires burn at an extreme intensity and spread through the crown or canopy of trees. The influence of wind is greater in the tree canopy and these fires spread very quickly, especially when the tree canopy is interconnected or continuous.
Our approach to fire management
The NPWS Fire management direction statement sets out our long-term, sustainable approach to managing fire. It outlines how we are responding to changing conditions and identifies the priorities guiding our fire management program.