Environment

‘Rolling the dice’: Sydney faces challenging fire season, charts show

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The Sydney region will enter spring primed for large bushfires after its third dry winter in a row, with maps showing moisture levels are below those in the run-up to the blazing 2013 season.

Moisture levels of trees and other live vegetation for the fortnight up to August 12 show much of the region around Sydney to be dry, particularly to the north-west and in the Blue Mountains.

The dry conditions mean it is likely all forested areas in the state will have the start of their dangerous bushfire period brought forward to September 1, the NSW Rural Fire Service said.

A bushfire near Springwood in the Blue Mountains in October 2013. Dry conditions this winter have fire experts wary of the coming season.

A bushfire near Springwood in the Blue Mountains in October 2013. Dry conditions this winter have fire experts wary of the coming season.Credit:Dallas Kilponen

"It's dry across the Sydney basin," said Rachael Nolan, a fire ecology lecturer at Western Sydney University who compiled the data from satellite imagery. "Our research shows when the live stuff dries out, you're more likely to get the more severe fires."

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Fire agencies and researchers caution that having dry forests or grasslands don't guarantee Sydney will have major bushfires. Those events also need favourable fire weather and ignition points.

Sydney, in fact, has had three consecutive dry winters but largely avoided big blazes in the springs of 2017 and 2018. Strong cold fronts, which draw in blustery, hot north-westerly winds ahead of them, were largely absent.

"We're rolling the dice again," said Ross Bradstock, director of the Centre for Environmental Risk Management of Bushfire at the University of Wollongong.

"It's the third year in a row we've been relatively dry for this time of year. Whether we get away with it again this year, I can't tell you."

Compared with last year, median live fuel moisture content remains slightly higher than last year but is heading in the same downward direction.

Moisture levels were higher, though, than for the same time in 2013, which preceded the big blazes in Springwood and elsewhere that spring, Dr Nolan said.

Researchers monitor moisture level trends in live vegetation closely as they can be a better guide to fuel conditions than dead material, such as fallen trees, which can fluctuate more.

Drying trees also drop leaves, adding several tonnes of material to the forest floor per hectare.

"It can top up the fuel loads," Professor Bradstock said. "It's not trivial."

After several relatively dry years, it is also likely that there will be more dead trees to burn, Dr Nolan said.

Fire season starts early

Ben Shepherd, a senior RFS spokesman, said Dr Nolan's data dovetailed with agencies' findRead More – Source