Image of the Roleystone bushfire (February 2011)
Each year in Western Australia, thousands of fires occur that destroy or damage houses, sheds, garages, commercial and industrial buildings, vehicles and vast areas of bushland. Some of these become critical events subject to size, location or prevailing weather conditions.
Bushfire is a term used commonly in Australia to describe fires burning in natural vegetation, including (but not limited to) in a forest, a shrub land, a grassland, a crop or pasture or a tree plantation. They can start suddenly and move quickly, affecting large areas. Bushfires are often described in terms of their rate of spread (metres or kilometres per hour) and the size of their flames.
Like all fires, a bushfire needs fuel, oxygen and an ignition source to start. Common ignitions for a bushfire are lightning, accidental ignition and arson. While many fires start due to arson, Western Australia is also prone to dry lightning, creating fires in remote regions, where fire fighting can be difficult. Fire intensity and the speed at which a bushfire can spread are dependent on key factors: fuel load, fuel moisture, temperature and relative humidity.
Wind speed and slope angle also influence fire behaviour.
Bushfires occur right across Western Australia; however the areas most prone to fire are those with high fuel loads such as the Southwest and the Kimberley.
The fire season varies across the state. The northern fire season occurs between June and October, during the dry season, while the southern season occurs during the long hot summer between November and April.
Low and unreliable rainfall, coupled with hot air and warm temperatures lower the moisture content of vegetation, increasing the potential speed of a fire, particularly in high winds. In addition, extended periods of dry weather that follow a period of good rainfall also present a high fire danger as the rainfall is likely to have encouraged growth of vegetation. This vegetation then dries and cures, increasing fuel for the fire.
The Fire Danger Rating (FDR) is based on forecast weather conditions and indicates the threat of bushfire on a given day. The fire danger rating goes from low-moderate, right through to catastrophic and with each rating, the fire behaviour and potential impacts may vary.
While the impacts of bushfire are typically geographically limited, the impacts can be severe. Loss of life and damage/destruction of property caused by the fire may occur within the fire ground. Further afield, the impacts of smoke on health and transport can be severe. In addition economic impacts often result from recovery costs required to repair infrastructure as well as knock-on economic effects due to the closure of roads, airports and other key infrastructure and services.
Physical controls Prescribed burningBack burning Water bombingLand use planning Total fire ban
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