A wildfire, also known as a wildland fire, forest fire, vegetation fire, grass fire, peat fire, bushfire (in Australia and Asia), or hill fire, is an uncontrolled fire often occurring in wildland areas, but which can also consume houses or agricultural resources. Common causes include lightning, human carelessness, arson, volcano eruption, and pyroclastic cloud from active volcano. Heat waves, droughts, and cyclical climate changes such as El Nińo can also have a dramatic effect on the risk of wildfires.
Wildfires are common in many places around the world, including forest areas of the United States and Canada, where the climates are sufficiently moist to allow the growth of trees, but feature extended dry, hot periods particularly in the Summer, fall, and in time of drought when fallen branches, leaves, and other material can dry out and become
highly flammable. Wildfires are also common in grasslands and scrublands. Wildfires tend to be most common and severe during years of drought and occur on days of strong winds. With extensive urbanization of wildlands, these fires
often involve destruction of suburban homes located in the wildland urban interface, a zone of transition between developed areas and undeveloped wildland.
Wildfires often cause large-scale damage to private or public property, destroying many homes and causing deaths, particularly when they have reached urban fringe communities.
Extremely dry grass and shrubs along with dry leaves, wood chips, bark chips and other small, rotten, misshapen, or otherwise undesirable
wood pieces discarded during logging has often provided the fuel for devastating fires such as the fires in Michigan in the 19th century.
The aftermath of a wildfire can be as disastrous if not more so than the fire. A particularly destructive fire burns away plants and trees that would otherwise prevent surface soil erosion. If heavy rains occur after such a fire, landslides, ash flows, and flash floods can occur. This can result in property damage outside the immediate fire area, and can affect the water
quality of drinking water, streams, rivers and lakes.
In southern California, under the influence of Santa Ana winds, wildfires can move at tremendous speeds, up to 40 miles (60 km) in a
single day, consuming up to 1,000 acres (4 km˛) per hour. Dense clouds of burning embers push relentlessly ahead of the flames crossing firebreaks without pause.
Powerful updrafts caused by a large wildfire will draw in air from surrounding areas. These self-generated winds can lead to a phenomenon known as a firestorm.
On average, wildfires burn 4.3 million acres (17,000 km˛) in the United States annually. In recent years the federal government has spent $1
billion a year on fire suppression. 2002 was a record year for fires with major fires in Arizona, California, Colorado, and Oregon.
People living in fire-prone areas need to take a variety of precautions, including building their homes out of flame-resistant materials,
reducing the amount of fuel near the home or property (including firebreaks, their own miniature control lines, in effect), maintaining emergency survival supplies and be ready for often mandatory evacuations.