AskDefine | Define bushfire

User Contributed Dictionary

English

Noun

  1. An Australasian wildfire

Extensive Definition

A Bushfire is a fire that occurs in the bush (collective term for scrub, woodland or grassland of Australia, New Zealand, New Caledonia). In south east Australia, bushfires tend to be most common and most severe during summer and autumn, in drought years, and particularly severe in El Niño years. Subsequently south east Australia is considered one of the most fire prone areas of the world. In the north of Australia, bushfires usually occur during winter (the dry season), and fire severity tends to be more associated with seasonal weather patterns. In the southwest, similarly, bushfires occur in the summer dry season and severity is usually related to seasonal growth. Fire frequency in the north is difficult to assess, as the vast majority of fires are caused by human activity, however lightning strikes can cause bush fires too.

History

The natural fire regime was altered by the arrival of humans in Australia. Fires became more frequent, and fire-loving species — notably eucalypts — greatly expanded their range. It is assumed that a good deal of this change came about as the result of deliberate action by early humans, setting fires to clear undergrowth or drive game.
Plants have evolved a variety of strategies to survive (or even require) fires, (possessing reserve shoots that sprout after a fire, or developing fire-resistant or fire-triggered seeds) or even encourage fire (eucalypts contain flammable oils in the leaves) as a way to eliminate competition from less fire-tolerant species. Many native animals are also adept at surviving bushfires. Many animals become extinct from bushfires destroying their habitat.

Bushfire control

Key Factors affecting bushfires

• Fuel: Anything that burns is fuel for the fire: litter on the ground (leaves, twigs, rubbish), undergrowth (shrubs, grass, seedlings), trees and other vegetation, structures (such as your house) and any miscellaneous stuff laying about; gas bottles, piles of firewood, tyres, etc. Ladder fuels are low growing (30 cm to 2 meters) vegetation that offers a ladder for the fire to rise to the canopies of trees.
• Weather: Weather is a major contributor to bushfires. The hotter and dryer, the more likely it is for a bushfire to start and spread uncontrollably. High winds will reduce humidity, and cause an already started bushfire to spread more rapidly. Most bushfires start in the afternoon, when it is driest and hottest.
• Topography/slope: The topography of the terrain is a major factor in bushfire behaviour. Generally the fire spreads faster uphill. Conversely, fire going downhill advances more slowly. The superheated air is pushed in front of the fire drying and pre-warming the fuel for ignition. When a fire progressing downhill hits the flat at the bottom of the hill, the height of the flame can quadruple, when the fire hits the undulating slope opposite, the height may quadruple again. In other words, 1 metre flames going downhill can turn into 4 metre flames at the bottom of the hill, and to 16 metre flames starting to climb the next hill. While the height of the flame depends mainly on the height of the fuel, the former stands as a reminder that an innocent looking small bushfire can rapidly change into a life threatening fire.

Firefighting Methods

In National Parks and reserves, bushfire fighting is carried out by professional staff, such as Rangers, Park Workers, Field and Technical Officers, with help from volunteers from rural areas. The rural areas have bush fire services, E.g the CFA, largely staffed by volunteers, to help control bushfires. As with large fires on public land it is common for Parks staff and Rural or Country volunteers to work together on large rural fires. On some occasions urban firefighting professionals are also called in to assist. As well as the water-spraying trucks commonly used in urban firefighting, bushfire services often own or lease aircraft, particularly fire helicopters, that can douse areas inaccessible to ground crews. However, large fires are often of such a size that no conceivable firefighting service could attempt to douse the whole fire directly, and so alternative techniques are used.
Typically, this involves controlling the area that the fire can spread to, clearing control lines which are areas which contain no combustible material. These control lines can be produced by bulldozing, or by backburning — setting a small, low-intensity fire to burn the flammable material in a controlled way. These may then be extinguished by firefighters, or, ideally, directed in such away so that they meet the main fire front, at which point both fires will run out of flammable material and be extinguished.
Unfortunately, such methods can fail in the face of wind shifts causing fires to miss control lines, or because fires jump straight over them (for instance, because a burning tree falls across a line, or burning embers are carried by the wind over the line).
The actual goals of firefighters vary. Protection of life (both the firefighters and civilians) is given top priority, then private property according to economic and social value. In very severe fires, this is sometimes the only possible action. Protecting houses is regarded as more important than, say, machinery sheds, though firefighters, if possible, will try to keep fires off farmland to protect stock and fences (steel fences are destroyed by the passage of fire, as the wire is irreversibly stretched and weakened by it). Preventing the burning of publicly owned forested areas is generally of least priority, and, indeed, it is quite common (in Australia, at least) for firefighters to simply observe a fire burn towards control lines through forest rather than attempt to put it out more quickly — it is, after all, a natural process.
The risk of major bushfires can be reduced by reducing the amount of fuel present. In forests, this is usually accomplished by conducting controlled burns — deliberately setting areas ablaze during favourable weather conditions in spring or autumn. Controlled burns can be controversial, both because they can be regarded as tampering with the forest ecosystem, and because serious fires can be started if a control burn gets out of hand. The Australian Aborigines used controlled burning to encourage new growth of plants.
Contrary to urban understanding of bushfire, rural farming communities are comparatively rarely threatened directly by them. They are usually located in the middle of large areas of cleared, usually grazed, land, and in the drought conditions present in bushfire years there is often very little grass left. However, urban fringes often spread into forested areas, and communities have literally built themselves in the middle of highly flammable forests.
On occasions, bushfires have caused wide-scale damage to private property, particularly when they have reached such urban-fringe communities, destroying many homes and causing deaths.
In fire-prone areas, people living in them typically take a variety of precautions. These include building their home out of flame-resistant materials, reducing the amount of fuel near to the home or property, constructing firebreaks, and investing in firefighting equipment.

Significant bushfires

Notable bushfire events

Bushfire gallery

Notes and references

External links

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