Fire

Tara on Tour

Australia is known to have some of the worst bush fires/wild fires in the world, with Southern California following a close second. In areas where there are very dry conditions, and forestation, the risk of fire is very high and it takes only a casually discarded match or an unguarded campfire to start a blaze that will wipe out acres of land and endanger wildlife and human life. Many fires are also ignited by lightning or by power lines, vehicle crashes or sparks from farm machinery. These are the accidental fires. Many more are started deliberately and arson has caused considerable damage in areas where vegetation burns like tinder.

The Fire Danger Index, used in Australia, calculates risk factors such as temperature, relative humidity, wind speed, drought and the availability of fuel in any given area. The most dangerous combination is high temperature, low humidity, high winds and lack of rain. Bushfires spread as a thin front of flames as can be seen in the photograph. Forest fires normally travel at 1-3 km/h, and have flames of between 10 and 20 metres. Grass fires travel faster: 3-10 km/h but occasionally they have been known to travel as fast as 25 km/h. The stronger the wind, the faster the fire will spread. It's the hot, dry winds blowing from the central arid region of Australia that produce such favourable conditions for fire.

During the heatwave in Britain earlier this year, a wildfire in the county of Surrey resulted in the loss of several acres of heath at Thursley Common. Firefighters in this part of the world had to tackle the kind of fire normally reserved for hotter, drier climates, and it alerted the country to the higher risk of such incidents particularly during very hot, dry spells. There is a general consensus that Britain's firefighters will be dealing with similar incidents more often in the future, and provision is being made for suitable training and equipment.

So, have fires always been a problem for the Earth? Well, according to research undertaken by a London-based geologist, who specialises in the study of charcoal, fires were once quite rare. But this was a very, very long time ago: during the first 50 million years of plant evolution in fact. From around 365 million years ago, severe fires became widespread over the planet, and this was in part caused by rising oxygen levels. Fires need oxygen to burn and when oxygen levels were at their peak (some 275 million years ago), even damp vegetation would have ignited very easily. We are not at the same risk today, but it is clear that global warming is having an impact on our climate in so many ways - and the incidence of wildfire is likely to increase.