THE RAGE: This moderate resolution imaging spectroradiometer (MODIS) handout image captured on NASA’s Terra satellite on January 3 and received on January 7 shows smoke from the Adelaide Hills fires over South Australia state. Authorities said they had largely contained a destructive bushfire in the country’s south but would remain vigilant against potential flare-ups with a heatwave set to send temperatures soaring. — AFP
By Steff Gaulter
Fires have been raging in Australia. They are the worst wildfires that the state of South Australia has seen in over thirty years and they’ve destroyed at least fifty homes.
Wildfires are a regular hazard of the Australian summer, but it’s the scale of the current blazes which are causing concern. They’re said to be the worst fires that have hit South Australia since the Ash Wednesday fires of February 1983. These fires killed 75 people and destroyed thousands of homes. The mere mention of the Ash Wednesday fires still brings horrific memories to many residents of South Australia and Victoria.
The threat of wildfires is something that residents in Australia have had to learn to live with. They’re a little like tornadoes in the US or monsoon flooding in Asia; every year somewhere will be devastated, but all that the locals can really do is to hope their homes will be spared.
As you might expect, the fires usually burn in the summer months, which in the southern hemisphere is between December and February. This is when the air is hottest and the vegetation is at its most dry.
The biggest fire risk occurs when the winds blow south from the desert interior. This brings hot, dry weather across the southern states. If the air were humid then the sun would also have to heat the moisture in the air, as well as the air itself; therefore, the low humidity of the desert air helps the temperature to climb very high.
As the heat soars, the low humidity also ensures the landscape is extremely dry, aiding the spread of the fires. Once a spark has ignited a fire, if there is a strong wind this will make the spread of the wild fire almost impossible for firefighters to contain.
Australia is particularly prone to bushfires as the continent is so dry. Adelaide for example, expects slightly less rain than London in the UK, but the annual temperature is about 7°C (12.5°F) higher. This ensures that Adelaide has a far greater evaporation rate than London and the vegetation largely dries out during the summer, providing plenty of brittle debris to fuel wildfires.
The fires are terrifying in themselves, but these huge wildfires have also been known to generate their own type of weather. The fires create immense heat and draw moisture from the trees as they burn. This combination of heat and moisture can generate clouds, storms and even tornadoes.
As the fire rages, the hot air near the flames will rise. This means a column of warm, moist air will rise high into the atmosphere and as the air rises away from the fire, it will gradually cool. Cool air cannot contain as much moisture as warm air, so as the air rises, water droplets will condense and if there is enough moisture, a cloud will form. This type of cloud is called a pyrocumulus cloud, but it looks and behaves the same way as a normal cloud: it builds like a typical cloud, drifts in the direction of the wind and has even been known to generate rain. Sometimes this rain may help the firemen to extinguish the flames.
It’s also possible for the particles moving within the pyrocumulus cloud to rub together and create thunder and lightning. This can cause new problems, because lightning is often the cause of wildfires, so more sparks can ignite yet more flames.
The major problem from this type of storm, however, is the wind it generates. Hot air is rising into the thunderstorm, but elsewhere air is sinking. Strong, sudden gusts of winds can be hazardous for firefighters and those trying to defend their homes, as they can cause the fire to change direction unexpectedly.
However, by far the most shocking type of weather that has been triggered by a huge wildfire was a fire tornado. Only one has ever been confirmed, and that hit a suburb of Canberra in 2003. Before this, researchers had only been able to speculate that it was theoretically possible for a fierce blaze to produce one. Never before had enough evidence been collected to give conclusive proof of their existence.
However, after studying weather observations, radar data, videos and photos, researchers at the Emergency Services Agency in the Capital Territory found the proof they needed.
The 2003 fire tornado certainly wasn’t a feeble one. It was an EF2, a level two on the five-point Enhanced Fujita scale used to rate the severity of tornadoes. Although the tornado was towards the lower end of the scale of intensity, the winds of over 178kph (111mph) were still strong enough to rip roofs from houses and blow cars off roads.
The fire tornado tore towards Canberra and by the time it reached the suburb of Chapman it had a diameter of nearly half a kilometre (0.3 miles). It marched steadily forward at 30kph (20mph), but on the ground, with all the other fires and the general confusion, it was barely noticed. This gives a clear indication on just how serious the situation becomes during a wild fire. The flames and strong winds, combined with the fear, panic and confusion, mean that an EF2 fire tornado was hardly noticed.
No-one wants to see another fire tornado, but as the summer wears on in Australia, I think it would be fair to say that no-one wants to see another wildfire either. All the locals can do is wait for the end of summer.
