KEY POINTS:
Why are we asking this now?
More than a dozen fast-moving wildfires, driven by dry, gale-force Santa Ana winds, have raged across southern California, killing at least five people, injuring dozens of others and forcing about 880,000 people to flee their homes.
The fires are estimated to have charred 81,000ha and have closed state highways, schools, hospitals, rest homes and businesses.
Desperate fire officials have called for help from other states to suppress the fires, which have sent plumes of thick black smoke drifting across much of the state, blotting out the sun.
What are wildfires?
A wildfire, also known as a wildland fire, forest fire, vegetation fire, grass fire, bushfire, or hill fire is an uncontrolled fire often occurring in bushland, but which can also consume urban areas.
They can be caused by heat waves, droughts, lightning strikes, climate change, volcanic eruptions and pyroclastic cloud.
However, they are often caused by human arsonists or carelessness.
Where do wildfires occur?
As well as the forested areas of the United States and Canada, they are common in many other countries, including vegetated areas of Australia and bushland in the Western Cape of South Africa.
Fires are particularly dominant in summer and autumn, and during droughts when fallen branches, leaves, and other material can dry out and become highly flammable.
They usually occur on days when there are strong winds.
They are not so common in New Zealand but it is estimated about 2000 wildfires burn through 7000ha of forest lands a year.
Why are wildfires so dangerous?
They can cause colossal damage, engulfing up to 404ha in 30 minutes. They can kill humans, wildlife and destroy buildings.
About 5 per cent of lightning bolt fires burn out of control.
How are they put out?
Firefighters usually work around the clock for days, or even weeks, to suppress the fires using water pumps or dropping special chemicals from planes and helicopters to smother the flames.
Fire officials also help out with evacuations and crowd control in urban areas.
Rain, lack of wind, or lack of fuel may slow the fire down. Fire is also usually more controllable at night when winds die down.
How can you prevent a wildfire?
The risk of major wildfires can be minimised by reducing fuel in bushland.
Some countries conduct controlled burns under less dangerous weather.
People living in fire-prone areas usually take precautions, including building their homes with flame-resistant materials, reducing the amount of fuel near the home, and investing in their own firefighting equipment such as extinguishers.
Many countries, including Australia, France and Germany, still use fire lookouts to detect forest fires.
A lookout is a person assigned to look for fire from a tower.
