Even a stray spark from a camp fire could accidentally start a bushfire. For example, a person may accidentally let a small fire get out of control. Unexpected sparks from machinery, electrical systems and power lines can also start fires.
Controlling ignition — where heat can spark a fire — is a big part of reducing bushfires. A total fire ban means nobody is allowed to start a fire in that area, even a small camp fire.
Plants provide the fuel for bushfires. Dried grass and leaf litter are most likely to burn. Some plants burn more easily than others; some such as succulent plants are quite difficult to burn and others such as eucalyptus trees burn very easily. The more fuel there is for the fire to burn, the bigger the fire. Dry leaf litter on the ground can provide a lot of fuel for a bushfire. Most loss of life and economic damage occurs around the fringes of cities where homes are commonly in close proximity to flammable vegetation.
A comparison of disaster cost estimates in Australia. International J of DRR. Report with AGD. Geoscience Australia is committed to support Australia's capability to managing the impact of natural hazards, including bushfire. Geoscience Australia:. Geoscience Australia supports emergency managers' ability to respond to, and prepare for, bushfires, including providing satellite information to inform emergency managers and the general public of where bushfires have been occurring. Geoscience Australia also develops fundamental datasets and tools to model the potential impact of bushfire.
In particular, Geoscience Australia:. What is a bushfire? While naturally occurring bushfires cannot be averted, their consequences can be minimised by implementing mitigation strategies and reducing the potential impact to areas which are most vulnerable What factors create a favourable environment for bushfires to occur?
Fuel load Fuel load describes the amount of fallen bark, leaf litter and small branches accumulating in the landscape. Fuel moisture Dry fuel will burn quickly, but damp or wet fuel may not burn at all. 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. Ambient temperature The higher the temperature the more likely it is that a fire will start or continue to burn.
Relative humidity Dry air promotes a greater intensity fire than moist air. Slope angle Fires pre-heat their fuel source through radiation and convection. Ignition Source Bushfires can originate from both human activity and natural causes with lightning the predominant natural source, accounting for about half of all ignitions in Australia. Where do bushfires occur?
In the years between and , major Australian bushfires have resulted in over injuries and fatalities, close to 50 per cent of all deaths from major Australian natural disasters in the period excluding heatwaves. A fire front advances more quickly when travelling upslope and slows travelling down slope. These gases react with oxygen in the surrounding atmosphere. The actual flames of the fire are the release of some of the heat energy as light.
Remove any one of these and fire cannot sustain itself. Interactive The fire triangle For fire to continue burning, it needs oxygen, heat, and fuel—the three components of the "fire triangle". Remove one of these components to put out the fire.
When you pour water onto a fire, the heat of the fire causes the water to heat up and turn into steam. This is a very energy-intensive reaction, and it sucks away the heat which is a form of energy of the fire. This leaves the fire without enough energy to keep burning. Predicting when and where bushfires are likely to occur is obviously an important and useful part of bushfire management.
It will be particularly important across many parts of Australia where the number of days of extreme fire danger are projected to increase under climate change. The Australian bush, though it has a reputation for being dry and scrubby, varies greatly from place to place around the country. There are regions of open woodlands, grassland savannas, dense rainforest. A bushfire will burn anything that it finds in its path, but different types of vegetation burn differently. Generally, fuel is classified as being fine grasses and twigs that are less than 6 millimetres in diameter or heavy branches, logs or stumps.
Finer fuels burn more easily, feeding the spread of the fire, but heavier fuels burn with greater intensity, creating more heat and making the fire more difficult to put out.
Fuel loads accumulate in different types of vegetation at different rates. In Western Australia, jarrah Eucalyptus marginata forests build up fuel at a rate of around 1—2 tonnes per hectare per year, while karri Eucalyptus diversicolor forests accumulate around 3—4 tonnes of fuel per hectare per year. View video details and transcript.
Another key factor is fuel moisture, or how dry the bush is. The drier the fuel, the more easily it will burn. Fuel fits into two main categories: live and dead. These depend on recent rainfall and temperatures.
Researchers are developing methods of using remote sensing data from satellites or aircraft to detect the relative dryness of the bush. One way satellites can estimate fuel moisture is by picking up changes in the greenness of vegetation, an indicator of vegetation dryness. This is particularly important in grasslands.
The key controls on the dryness level in fine fuels are relative humidity, temperature and recent rainfall. Certain weather conditions fuel a fire and help it burn. Long-term seasonal weather patterns, such as periods of drought or rainfall, can affect the availability and moisture content of vegetation and the fuel available for a fire to burn.
A fire is much more likely to ignite, and continue to burn, in hot, dry and windy weather. Other causes can be faulty electrical wires, a cigarette carelessly tossed out of a car window, a hazard reduction burn gone wrong, arson, or accidental igniton. The primary influences upon how bushfires move through the landscape are humidity, geography, wind and temperature.
The effects of ambient temperature and humidity on a fire are pretty obvious. The hotter the air temperature, the closer any fuel is to its ignition point, and dry fuel will burn more easily. The lower the humidity, the drier the air is, again helping fuels burn as they release their moisture into the air more readily. The slope of the landscape is also important.
Just consider a match and how much faster it burns when you hold it so that flame is burning up the stick and towards your fingers! Similarly, fires burn much faster uphill than down. This is because the radiation and convection a fires creates preheat the fuel source, and this is much more readily done upslope than down. A degree increase in slope usually results in a doubling of the speed of the fire. Fire will spread up a degree slope four times as fast as it will along flat ground.
Going uphill Fire moves faster uphill because there is less space between the flames and new fuel to burn. Also, the radiant heat caused by the fire pre-heats the fuel, making it easier to ignite. The increased distance between flames and new fuel means fires spread more slowly when moving downhill unless the slope of the land creates unusual air currents.
However, if wind speeds are even slightly higher than this, they will have a significant impact on the fire movement. A change in wind, often from a cold front, can activate the side of a fire, making it broader.
In general, a wider fire will burn faster than a very narrow one. They can start from human activity - either accidently or deliberately - or can start by natural causes like lightning.
Bushfires often pass in just a few minutes but can smoulder for days. High winds are a real threat as they can fan the flames and spread the blaze. The danger period for bushfires varies across a country depending on the climate. For most of southern Australia, the danger period is summer and autumn. For New South Wales and southern Queensland, both in the east of Australia, the highest risk is usually in spring and early summer.
The Northern Territory has most of its fires in winter and spring.
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