The previous earliest total fire ban in Sydney was on September 5, 2012 - almost three weeks later in the warming season than this Wednesday's ban - according to the Herald's archives. Loading While the big dry has drawn much attention - all of NSW was declared in drought earlier this month - the driest start to a year in the state since 1965 and record daytime temperatures have fed growing concern among fire researchers for some time. For Sydney, year-to-date daytime temperatures have averaged 23.7 degrees, eclipsing the previous highest of 23.6 degrees in 2016, the Bureau of Meteorology said. "It will take a lot of rainfall to make up for that moisture deficit," RFS Deputy Commissioner Rob Rogers said.

Authorities are "very concerned" about the fire season ahead, and if we don't get those spring rains, "we're going to be entering uncharted territory", Mr Rogers said. "It's certainly extremely dry," he said. "It's three months since the end of the last fire season and now we're back into it again." The latest maps of fuel moisture content generated by teams at the Western Sydney and Wollongong universities obtained by Fairfax Media show large areas around Sydney are drier than this time in 2013. That year was marked by large springtime blazes that destroyed about 200 homes in the Blue Mountains alone.

Wind and warmth Owen Price, a senior researcher at the University of Wollongong's Centre for Environmental Risk Management of Bushfires, said several months without any significant rain had elevated the fire danger. "If we don't get any good rain, then the fire season is essentially starting now," Dr Price said. Temperatures on Wednesday climbed into the mid-20s or higher across much of the state and winds whipped to 109 km/h at Bellambi near Wollongong, creating dangerous fire conditions. Loading Replay Replay video Play video Play video

"When these variables interact - the winds and the high temperatures together - you get far more evaporation and far more fire behaviour," Dr Price said. "It's all bad." Fuel moisture mapping, developed with remote sensing, picks up the rate live plants are drying out and also the dampness of dead material, such as leaves and branches on the forest floor. "Live fuel moisture tells us more reliably what the current conditions are," said Rachael Nolan, a lecturer at Western Sydney's Hawkesbury Institute for the Environment, who helped compile the mapping. Loading Historically, live fuel moisture content levels that fall below the 101.5 per cent level (represented in the brown patches in the charts) correspond to a big increase in fire activity, Ross Bradstock, director of the University of Wollongong's fire centre, said last year.

The RFS, which last month brought forward the official start to the bushfire danger period to parts of the state's north-east - on Wednesday announced four local government areas would start their official fire seasons from this Friday. The areas are Bellingen, Coffs Harbour, Kempsey and Nambucca. RFS Commissioner Shane Fitzsimmons said hundreds of firefighters had to respond to dozens of

escaped and illegal burns on the weekend "when irresponsible landholders lit up in windy conditions". There were 48 instances of illegal fire activity reported between August 10-12, with around half occurring in the Greater Sydney, Greater Hunter and Central Tablelands regions alone, up from 38 incidents statewide the previous weekend. According to Rob Smalley, a climatologist with the Bureau of Meterology, the first seven months of the year were the state's warmest on record, beating the previous record set only a year ago by almost half a degree - a significant jump.