Prescribed burn-offs have little impact on reducing the extent and intensity of bushfires, a study in Tasmania has found.

Burn-offs are a routine part of preparations for bushfire season, but modelling suggests fire authorities need to target unrealistic amounts of land to have any meaningful effect on taming future wildfires.

The aim of prescribed burning is to reduces the amount of combustible material in the bush so that if a fire starts it won’t spread as far or be as intense.

To test how much prescribed burning would be needed to reduce the intensity and extent of a future bushfire, researchers from the University of Tasmania’s school of biological sciences simulated more than 11,000 fires on a typically dangerous fire-weather day in the apple isle.

They found that firefighters would need to carry out prescribed burn-offs across 31% of Tasmania in order to have a significant impact on reducing the threat from wildfires.

More realistic smaller-scale burn-offs, however, had almost no effect on the extent and intensity of a wildfire.

Professor David Bowman, who helped lead the study, said the findings suggested that planned burn-offs were still necessary but not sufficient.

Planned burning is a necessity but in my opinion not sufficient approach. Professor David Bowman, study co-leader

He said governments and fire authorities needed to consider taking a more local approach, and introduce on the outskirts of towns and cities clever landscape designs that included irrigation and green fire breaks in the form of parklands, that could work in conjunction with burn-offs to help mitigate bushfire risks.

“This is of global significance, to try to work out how we are going to coexist with flammable landscapes with an accelerating risk of climate change, which is shrinking the safe days to do planned burning but heightening the number of dangerous days when there will be uncontrolled bushfires,” he said. “There’s no question we need fuel management, there’s an urgent need.

“Planned burning is a necessity but in my opinion not sufficient approach particularly at the broad scale. We have to start going local.”

Bowman said the downsides of relying on planned burn-offs to mitigate bushfire risk included smoke haze, which can cause breathing difficulties for many people, as well as the fact that the blazes can run out of control and can’t be carried out in extremely dense bushland.

He acknowledged it could be expensive to introduce landscape designs to help counter bushfires, but argued they were a necessary cost for state and local governments.

“If we think about earthquakes you don’t hear people complaining, certainly in New Zealand, about the cost of a house that’s going to survive an earthquake,” Bowman said. “Yet in the fire space we have some building regulations but surely having fire-safe communities is a good investment.”

The study was published in the International Journal of Wildland Fire on Friday.