Internationally, southern Australia and particularly the State of Victoria, New South Wales, South Australia and the island State of Tasmania, is commonly regarded as one of the three most landscapes on Earth prone to damaging bushfires. The other two are southern California and the Mediterranean coast.
Victorians live entirely within what the international renown fire historian, Stephen Pyne, calls “the bushfire flume.” It is the most distinctive bushfire region of Australia and one of the most dangerous in the world.
When a high-pressure system stalls in the Tasman Sea, hot northerly winds flow relentlessly down from central Australia across the densely vegetated south-east of the continent.
This fiery “flume” brews a deadly chemistry of air and fuel.
The mountain topography of steep slopes, ridges and valleys channels the hot air, temperatures climb to searing extremes, and humidity evaporates, such that the air crackles.
Fires starting under the influence of the strong north-westerly wind move quickly in a long straight line.
An unstable atmosphere with boiling pyrocumulonimbus cloud can also increase lightning and spot fires as burning leaves and bark get lifted up and carried through the air to start more fires downwind.
Typically, dry lightning storms without significant or any rainfall will roll across the landscape from the south-west with a strong cool change. The pattern of these storms begins before Christmas and continues well into autumn.
Depending on fuel dryness, the lightning storms often start numerous small fires on ridgetops as they strike dead trees. These trees ignite and bushfire spreads slowly for a while under the cooler conditions.
It is not uncommon for a single summer lightning storm to start as many as 50 to 100 small fires across the remote forests and mountains of eastern Victoria.
With a strong cool change, sometimes there is rain, but more often in summer and autumn, it is only a light sprinkle. Certainly not enough to extinguish any new blazes or wet the ground fuels.
After the south-west change has passed, the weather is typically benign for a few days with the development of a strong inversion layer and light winds. So new fires that have been started by lightning often smoulder undetected.
Combined with low clouds in the valleys these conditions make detection of any new fires from aircraft or firetowers difficult.
But there is also a chance to do some good suppression works before it gets hot and windy again.
Victoria’s Forests & Bushfire Heritage 