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A wildfire or wildland fire is an uncontrolled fire in an area of combustible vegetation that occurs in the countryside area. Other names such as brush fire, bush fire, forest fire, desert fire, grass fire, hill fire, peat fire, vegetation fire, and veldfire may be used to describe the same phenomenon depending on the type of vegetation being burned, and the regional variant of English being used. A wildfire differs from other fires by its extensive size, the speed at which it can spread out from its original source, its potential to change direction unexpectedly, and its ability to jump gaps such as roads, rivers and fire breaks.〔(【引用サイトリンク】 The Science of Wildland fire )〕 Wildfires are characterized in terms of the cause of ignition, their physical properties such as speed of propagation, the combustible material present, and the effect of weather on the fire.〔 Bushfires in Australia are a common occurrence; because of the generally hot and dry climate, they pose a great risk to life and infrastructure during all times of the year, though mostly throughout the hotter months of summer and spring.〔"(Bushfires - Get the Facts )". Attorney-General's Department (Australia), Retrieved 2013-01-09 .〕 In the United States, there are typically between 60,000 and 80,000 wildfires that occur each year, burning 3 million to 10 million acres (12,000 to 40,000 square kilometres) of land depending on the year.〔http://www.nifc.gov/fireInfo/fireInfo_stats_totalFires.html〕〔(Billion-Dollar Weather and Climate Disasters: Table of Events )〕 Fossil records and human history contain accounts of wildfires, as wildfires can occur in periodic intervals. Wildfires can cause extensive damage, both to property and human life, but they also have various beneficial effects on wilderness areas. Some plant species depend on the effects of fire for growth and reproduction,〔 although large wildfires may also have negative ecological effects.〔 Strategies of wildfire prevention, detection, and suppression have varied over the years, and international wildfire management experts encourage further development of technology and research. One of the more controversial techniques is controlled burning: permitting or even igniting smaller fires to minimize the amount of flammable material available for a potential wildfire.〔''Interagency Strategy for the Implementation of the Federal Wildland Fire Policy'', entire text〕〔''National Wildfire Coordinating Group Communicator's Guide For Wildland Fire Management'', entire text〕 While some wildfires burn in remote forested regions, they can cause extensive destruction of homes and other property located in the wildland-urban interface: a zone of transition between developed areas and undeveloped wilderness.〔 The name ''wildfire'' was once a synonym for Greek fire but now refers to any large or destructive conflagration.〔 Wildfires differ from other fires in that they take place outdoors in areas of grassland, woodlands, bushland, scrubland, peatland, and other wooded areas that act as a source of fuel, or combustible material. Buildings may become involved if a wildfire spreads to adjacent communities. While the causes of wildfires vary and the outcomes are always unique, all wildfires can be characterized in terms of their physical properties, their fuel type, and the effect that weather has on the fire. Wildfire behaviour and severity result from the combination of factors such as available fuels, physical setting, and weather.〔Graham, ''et al.'', 12, 36〕〔''National Wildfire Coordinating Group Communicator's Guide For Wildland Fire Management'', 4-6.〕 While wildfires can be large, uncontrolled disasters that burn through or more, they can also be as small as or less.〔(【引用サイトリンク】 Fire Information - Wildland Fire Statistics )〕〔(【引用サイトリンク】title=Definition of Map Terms )〕〔''Glossary of Wildland Fire Terminology, 156''〕 Although smaller events may be included in wildfire modeling, most do not earn press attention. This can be problematic because public fire policies, which relate to fires of all sizes, are influenced more by the way the media portrays catastrophic wildfires than by small fires.〔Alvarado, ''et al''., 66-68〕〔Olson, ''et al.'', 2-3〕 ==Causes== Wildfires are 'quasi-natural' hazards, meaning that they are not entirely natural features (like volcanoes, earthquakes and tropical storms). This is because they are caused by human activity as well. The four major natural causes of wildfire ignitions are lightning, volcanic eruption, sparks from rockfalls, and spontaneous combustion. The thousands of coal seam fires that are burning around the world, such as those in Centralia, Burning Mountain, and several coal-sustained fires in China, can also flare up and ignite nearby flammable material. The most common human sources of wildfires are arson, discarded cigarettes, sparks from equipment, and power line arcs (as detected by arc mapping). Ignition of wildland fires via contact with hot rifle bullet fragments is possible under the right conditions. In societies experiencing shifting cultivation where land is cleared quickly and farmed until the soil loses fertility, slash and burn clearing is often considered the least expensive way to prepare land for future use.〔Karki, 7.〕 Forested areas cleared by logging encourage the dominance of flammable grasses, and abandoned logging roads overgrown by vegetation may act as fire corridors. Annual grassland fires in southern Vietnam can be attributed in part to the destruction of forested areas by US military herbicides, explosives, and mechanical land clearing and burning operations during the Vietnam War.〔Karki, 4.〕 The most common cause of wildfires varies throughout the world. In Canada and northwest China, for example, lightning is the major source of ignition. In other parts of the world, human involvement is a major contributor. In Mexico, Central America, South America, Africa, Southeast Asia, Fiji, and New Zealand, wildfires can be attributed to human activities such as animal husbandry, agriculture, and land-conversion burning. Human carelessness is a major cause of wildfires in China and in the Mediterranean Basin. In the United States and Australia, the source of wildfires can be traced to both lightning strikes and human activities such as machinery sparks and cast-away cigarette butts."〔 On a yearly basis in the United States, typically more than six times the number of wildfires are caused by human means such as campfires and controlled agricultural burns than by natural means. However, in any given year there could be far more acres burned by wildfires that are started by natural means than by human means as well as vice versa. For example, in 2010, almost 1.4 million acres were burned by human-caused wildfires, and over 2 million acres were burned by naturally-caused wildfires. However, far more acres were burned by human-caused fires in 2011, when almost 5.4 million acres were burned by human-caused wildfires, and only about 3.4 million acres were caused by naturally-derived wildfires. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「wildfire」の詳細全文を読む スポンサード リンク
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