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Quickfire Science: Wildfires

Thu, 4th Jul 2013

Kate Lamble

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Nineteen fire-fighters were killed in Arizona this week tackling a ferocious wildfire that had got out of control. But how do blazes like this start Bushfire smoke east of Melbourneand how can we tackle them? Here’s the Quickfire Science with Hannah Critchlow and Kate Lamble...

Wildfires may be rare in some parts of the world, like Britain but an average of 50,000 start every year in Australia and over 4 million acres of woodland are destroyed annually in the United States

Wildfires are started after a period of hot dry weather converts green vegetation into a fuel source for a fire to spread, all it needs then, is a spark.

Up to 80% of wildfires are caused by humans – either through arson, or poor fire management such as unattended campfires or even just a discarded cigarette.

Natural triggers, such as lightning or even sparks caused by rockfalls can also start a fire.

Once started, a fire’s spread will be affected by the weather, the wind and the amount of fuel in the surrounding area. Under the right conditions they can move at a speed of up to 14 miles per hour.

When a fire starts we can tackle it by using aeroplanes and helicopters to drop large amounts of water or flame retardant chemicals, including phosphate fertiliser, over the blaze to try and slow it down.

On the ground, firefighters also spray the fire with water or chemicals including phosphate fertiliser.

Firefighters can also try and reduce the amount of fuel available to keep the fire burning – by creating a ‘fire-break’, removing vegetation in order to contain the fire.

They can also reduce the available fuel by starting back-fires – fires which burn towards the wildfire – using up any potential fuel in their path.

Some people think that by stopping small-scale wildfires in their tracks quickly we might actually be making fires more dangerous.

It stops small fires clearing old dry material from forests which can lead to an accumulation of fuel and a worse fire in later years.

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I know that some forest fires due to lightning
werttty, Wed, 11th Sep 2013

How accurate is the "80% figure"?  Perhaps it depends on where one is.

There were several large forest fires in Oregon this year.  I believe all of them were caused by lightning.  In particular mid-summer storms with lots of lightening, and very little rainfall. 

The majority of large Fir trees, and other evergreen trees can withstand the occasional forest fire, and it is not uncommon to see ancient trees with old fire scars.  However, it does depend on how hot the fire is.  There are estimates that fires once a decade or so can be healthy for a forest, and I believe the forest service does manage Yellowstone National Park by building small intentional fires.

Anyway, fires like the 2002 Biscuit fire can grow to be truly enormous.  I suppose I'd rather see small fire scars than seeing fires covering hundreds, or perhaps thousands of square miles. CliffordK, Wed, 11th Sep 2013

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