What is a bushfire?
A bushfire is a more general term than forest fire for the typical kind of wildfire that occurs in Australia. A bush is a collective term for scrub, woodland and grassland in Australia, New Zealand and New Caledonia. Consequently they do not only occur in wooded areas, but also (and very frequently) in the large Australian grasslands.
Causes
Natural processes are often the driving factor behind bushfires. They occur in several parts of the continent, depending on the season.
- During summer and autumn bushfires are most common and most severe in Southeast Australia – and then mainly 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 southwest too bushfires occur in the summer dry season, but here severity is usually related to seasonal growth.
- During winter and spring bushfires usually occur in the north of Australia (where winter is the local dry season), and fire severity tends to be mainly associated with seasonal weather patterns.
Although bushfires are strongly influenced by natural circumstances (lightning, volcanic eruptions, vegetation structure, climactic factors such as temperature and rainfall, topographical factors such as elevation and slope), many of them are nevertheless man-induced.
Bushfires have been a part of Australia’s nature for millions of years. The natural fire regime was profoundly altered by the arrival of humans in Australia. 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. This pattern was even worsened with the arrival of the first European settlers in the 18th century.
Seasonal fire distribution from April 1998 to March 1999 (left) and from April 1999 to March 2000 (right) as mapped from NOAA-AVHRR imagery - Source
Today it seems the human impact on bushfires is ever increasing. No longer just because of the direct effect on vegetation, habitation and other fueling infrastructure, nor just because many of the fires are man-induced (be it deliberately or accidentally), but also because of the global effect humans appear to have on the warming climate. Global warming affects many climate systems all over the world, and would also be responsible for the ever increasing drought in Australia, which induce more frequent and more severe bushfires.
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Fires detected by MODIS over a 10-day period for each image (left: summer and right: winter): 30/05/2000-08/06/2000 - 31/01/2001-09/02/2001 30/05/2008-08/06/2008 - 31/01/2009-09/02/2009 - Source: NASA
Effects
Bushfires have effects on nature as 
well as on humans. In nature most species are severely affected by fire. Most fauna and flora is instantly killed during a bushfire, but there are some species that manage to profit from – or at least survive – a bushfire: some plant species such as Eucalyptus even developed a lignotuber, a starchy swelling of the root crown as a protection against destruction of the plant stem by fire. Others, such as the Swamp Paperbark (Mullica rhaphiophylla) have the capacity to sprout new growth from groups of little buds under the bark. The dormancy of these buds is only broken by the heat of fire.
These processes are the result of millions of years of evolution, but as soon as man landed on the shores of the continent, fire regimes were altered. The resulting habitat changes have been widespread. Where fires became more frequent, for example, fire-resisting species - notably eucalypts - greatly expanded their range.
In addition to their impact on the environment, bushfires nowadays have a severe impact on life, health (through reducing air quality), property, infrastructure and primary production systems. Over the past 40 years, fires have claimed more than 430 lives, making them the most hazardous form of natural event in Australia.
Estimated fuel mass burnt across Australia in bushfires, forest fires and
agricultural fires between 1983 and 1998 - Source
Their financial cost, around AU$2.5 billion over the same period, represents about ten per cent of the total costs of natural disasters in Australia.
The majority of the impacts on life, property and infrastructure occur in southern Australia, where human settlement is greatest and where extreme fire weather conditions occur in most summers.
Just one example: Black Saturday
The deadliest bushfire ever recorded was the huge bushfire earlier this year, called the Black Saturday bushfires since they started in Victoria on and around Saturday 7 February 2009.
The weather conditions were extremely suitable for bushfires, resulting in Australia's highest ever loss of life from a bushfire: no less than 173 people died in the fires and about 500 were injured. The fires destroyed at least 2,000 homes and damaged thousands more. Many towns north-east of the state capital Melbourne were badly damaged or almost completely destroyed. In total, the Black Saturday bushfires affected 78 individual townships and left an estimated 7,500 people homeless.
The main causes of the fires were fallen or clashing power lines and arson. Other suspected ignition sources include lightning, cigarette butts and sparks from a power tool. More distantly implicated was a major drought that has persisted for more than a decade, as well as a domestic 50-year warming trend that has been linked to human-induced climate change. By early-mid March, favourable conditions aided containment efforts and extinguished the fires.
Source: Wildland Firefighter
Measures
Several measures can be taken when fighting the often devastating effects of bushfires.
- Since arson appears to be quite a common trigger of bushfires, Australia invests largely in arson-reduction programs, mainly focusing on school and community.
- Land use planning, development controls and building standards have a central role in reducing the risk to people and property from bushfire as well.
- Modification of elements of the landscape is a third important means of reducing risks to assets. Among the objectives of landscape modification are reducing the probability of a bushfire starting, slowing its spread, limiting its intensity so that it might be controlled, and maintaining ecological processes and biodiversity.
- Creating a mosaic of fire regimes across a landscape – with fire intervals, seasons and intensities in the mosaic appropriate for particular ecosystems – appears to be the best means of sustaining biodiversity and should be a goal of both ecological and fuel-reduction burning.
But apart from preventive measurements, Australia is also trying to be ready whenever a fire does occur. Readiness is important for both individuals and land management agencies. An incident management team needs to be ready to provide comprehensive operational information. The media have a particularly important role to play in conveying accurate and timely information.
The implementation of these two branches of bush fire policy – prevention and response – influence greatly the severity of the fires.
Fires have a fundamental and irreplaceable role in sustaining many of Australia’s natural ecosystems and ecological processes, and they are a valuable tool for achieving many land management objectives. However, if they are too frequent or too infrequent, too severe or too mild, or mistimed, they can erode ecosystem ‘health’ and biodiversity and compromise other land management goals—just as uncontrolled fires can threaten life, property, infrastructure, and production systems. It is an ongoing and increasing challenge for the people of Australia to keep fighting fires in a changing world.
Sources
Australia Bushfire Monitor
Australia: Victoria bushfires - The International Federation of Red Cross and Red Crescent Societies
Bush Fires in South Australia - Global Fire Monitoring Center (GFMC)
Bushfire incidents
Living in a land of fire - Australian Government
People and bushfires : factors affecting fire frequency - Australian Government
Report of the National Inquiry on Bushfire Mitigation and Management - Australian Government
Wikipedia Bushfire - Bushfires in Australia
Links
Earth from Space: ‘Black Saturday’ bushfires - ESA Observing the Earth
This page was written in 2009, as additional information to the poster series "10 years of Imaging the Earth"