Pacific weather links:
Get a grip on current conditions

Stormwatch:
Typhoons to tornadoes, we learn from 
the event

La Nina: 
What is going on with our planet's weather?

Profiles:
Legends in meteorology

Fire and water: After two wet winters, coastal New South Wales and south-east Queensland face massive fuel loads in the bush. Now, after a dry spring and conditions ripe for fire, the east coast is burning. Here a fire approaches the Nymboida River near Grafton, in northern NSW.

September 9, 2000

For the last two winters it seemed as if it would never stop raining. The bush bloomed ... and bloomed.

Much of Australia was under the influence of La Nina - a classic wet cycle. It was beautiful, and presented vivid and textured contrast to the bone-dry seasons which dominated the same region throughout the early 1990s.

But, for the bush fire brigades, forestry officials and national parks rangers, the big wet provided its own set of challenges. For instance, every time a hazard-reduction fire was ignited more rain would fall prevented the flames taking hold. Fuel loads in the bush - from the tall stands of timber to the spiny coastal heathlands - escalated to alarming levels.

Now La Nina is gone. This past winter has been dry and suddenly the north coast of New South Wales and south-eastern Queensland are facing a summer of drought. Water tanks are running dry and water transporters can’t keep up with demand. There is currently a 14 day wait for water deliveries in northern NSW.

On the heel of any water shortage comes the threat of bush fires and the season has begun so soon in the Australian sub-tropics that the official fire ban season was brought forward one month to September 1.

That move did little to prevent a severe outbreak of fires - most of them deliberately lit - between Gosford north of Sydney to suburban Brisbane.

When fire burns through coastal heath - especially when it burns hot, as it has done here near Broadwater NSW - little  is left on the ground. The exposed sandy soil, covered in fine ash, is so white it looks like snow. 

Normal spring months on the Australian east coast provide ample opportunity for fire danger. A string of low pressure cells migrate west to east across the Bight and through Bass Strait, so that their frontal cloud bands influence conditions way up into the sub tropics.

When these lows move through quickly, with one front following close on the heels of another, the winds over northern New South Wales blow typically from the north - preceding a front - then to the west, veering back to north again before the next front and rarely moving into the cooler, and wetter, southern sector.

The result is more hot and dry conditions followed by extremely windy westerlies - all of which provide food for fires.

Fire is also an essential part of the Australian bush. These Banksia seeds only open after fire. But if coastal heath is burned too often, plants and animals suffer. Banksia, for instance, need five years of growth before they can reproduce. The rare ground parrot needs heathland between seven and ten years old - a very specific eco-system, but one that probably matches natural burning. 

Australia’s fire season typically begins in northern NSW and southern Queensland from late September, spreading south to peak in Victoria and Tasmania in February.

This year is unusual in that there have been stronger westerly winds earlier in the year than average, according to Sydney forecaster Ben Bewick.

The seeds for this year’s fire season began in early August, when a blocked high to the east of New Zealand forced storm systems to the south. Northerly winds were the dominant feature over the Queensland and NSW border regions for more than a week.

Another blocking situation ten days later saw a massive low hang tight in Bass Strait, delivering an endless progression of north westerly winds over the same area. Fires lit to beat the new fire-ban season ignited quickly and burned with vigour.

When that low finally moved on, the front that followed was stronger still and moved across the country in less than 48 hours.

As it crossed the dividing range, a new low formed within the frontal cloud band, bringing dry westerly winds gusting to 44 knots.

In northern NSW, bush fire brigade volunteers and national parks and wildlife officers worked overtime to bring fires under control before the new low arrived, but fires lit in the Brisbane suburban area were fanned out of control.

That blow occurred on September 2. Three days later another front brought 40 knots winds to the central coast and brigades in the Gosford area had their work cut out for them. Three days after that, on September 8, another front crossed the coast bringing more westerly winds gusting into the high 30 knot range. Brigades and parks officers battled more than 30 fires from Seal Rocks, north of Newcastle to Kyogle on the Queensland border.

Strong winds prevented firefighters from battling blazes directly, and helicopters were used to water bomb from above.

Wind shifts, humidity and temperature are the things that firefighters consider when determining the direction and spread of a fire, says John Winter of the NSW Bush Fire Services Department.

"Weather factors are essential in determining how a fire will behave," he says. "Strong shifting winds make it almost impossible to directly attack fire."

Where back burning is not possible, firefighters may ‘shepherd’ a blaze into a controllable situation. They might burn ground cover along the flanks of a fire, forcing the main blaze to turn corners and end up against a rock cliff, for instance, where it can burn without spreading. Forcing fires towards creeks, roads and even the ‘great eastern firebreak’ (the South Pacific Ocean) all help to contain an otherwise uncontrollable blaze.

At the same time, forcing a fire into a gully may cause it to burn with new intensity - the wind drawing the fire up the gully much like a chimney. Anyone caught away from the protection of their vehicle in a gully fire is in grave danger.

This was the situation that trapped and killed two volunteers in a Lithgow blaze in 1997.

The real dangers of firefighting were brought home to the whole of Australia earlier this year when a routine hazard-reduction burn in Ku-ring-gai National Park north of Sydney trapped and killed four of the National Parks and Wildlife Service’s most experienced operators.

It was mid-winter, the surrounding soil and vegetation was moist and the fire occupied less than two hectares.

"Conditions were extremely benign," recalls Winter. "Temperatures were mild, winds were less than 10kph."

Parks officers were working the blaze on a moderately sloping ridge when a light and sudden wind shift apparently caught them unawares.

Three died on site, one later in hospital. One remains in critical condition and two have been released. Winter knew one of the victims and described him as the most experienced of bush men.

"Ku-ring-gai National Park was his back yard," notes Winter. "This event is a solemn reminder to us all."

Will anyone know exactly what happened?

"A lot of us still scratch our heads as to how such a fire run took place," says Winter. "And even after the State coroner investigates this fire, there is a good chance we will never really know what took place."

Back-burning involves fighting fire with fire. A blaze is ignited in front of a main fire, or along its flank. By keeping the back-burn from progressing forward, it will creep back towards the main front, helping to stop it in its tracks. However, a sudden wind shift or increase in wind strength can blow the back-burn up into the faces of those fighting the fire. Caution is a necessary tool when fighting fires in the bush

© weather-wise.com 2000

Who are we?

Advertise with us

Contact us