Australia Weather News

The trusty roadside fire danger signs marking the entrance to every country town are up for a revamp.

They are an Aussie icon, but the science behind the signs, the Forest Fire Danger Index, is now due for a rethink.

The Forest Fire Danger Index (FFDI) was originally created by the grandfather of Australian fire science, Alan McArthur.

He came up with his system by setting experimental fires in the hills around Canberra in the 1950s and 1960s.

It was a different time. Legend has it he used the number of beers needed to mollify firefighters to gauge fire intensity.

Whatever his methods, Mr McArthur's system has been used operationally since 1967 and has undoubtedly saved many lives.

The FFDI uses a combination of temperature, humidity, windspeed and drought factor to produce an indicator of how easy it will be for a fire to start, and how intense and fast moving the fire is likely to be once it gets going.

What's wrong with the system?

Despite its long tenure, recent major fires have shown the FFDI and its partner, the Grass Fire Danger Index (GFDI) have their flaws.

Rural Fire Service bushfire analyst Simon Heemstra agrees there are problems with the old system.

"There are quite a few examples of fire events in Australia where there has been a very big miss with the McArthur system," he said.

"There have been times when it has served us very well, but there are other times when it has missed."

These are a few of the major problems:

The top end sensitivity is a result of a formula created under lower fire danger conditions being extrapolated to extreme conditions.

Dr Heemstra said that sensitivity made it hard to precisely forecast what rating you were going to be in.

"It is possible to jump through several categories with very small changes in temperature, wind speed and humidity," he said.

NSW Rural Fire Service deputy commissioner Rob Rodgers said the difficulties with the top end of the scale were increasingly being put under the spotlight.

"The fires we see nowadays, when we start getting those catastrophic type fires, it was never designed to predict fires of that sort of magnitude," he said.

"It was always intended to predict fires of a much lower level."

Following the Black Saturday fires of 2009, a new category ("catastrophic" or "code red" in Victoria) was added to the roadside signs to describe conditions more extreme than those thought likely by McArthur.

The new system will go a step further by improving the formulas that form the basis of the rating system.

How will the new system help?

Having a more accurate gauge of the potential fire danger will help firefighters and the public better prepare.

It will also allow emergency services to have resources such as aircraft and firefighters at the ready when conditions are at their worst.

"There are never enough firefighters to cover the entire country, but hopefully this will enable us to put those firefighters where they're most needed and where the highest risk is," Mr Rodgers said.

He said the improved system would "undoubtedly" save lives.

"The more informed we are as community and firefighters, the better we're able to react and do that safely."

The prototype is being tested this fire season, and a review is being conducted into how the new system would have rated days when there were big fires in the past that were rated lowly on the old system.

Will the signs change?

Not yet.

Until researchers are sure their new method is an improvement, the current measures will stay in place.

But the signs are one of the things the team is looking into.

Few could deny a system where the second lowest level is "high" and there is a higher category than "extreme" has issues.

Social research considering public perception and responses to warnings is scheduled to begin next year.

But with this season forecast to have above normal fire danger for large areas, and high fire danger projected to be more common in the future, an improved index would be welcome.