Queensland Fire and Emergency Services commissioner Greg Leach says the climatic evidence indicates the seasons are changing and becoming longer, hotter and drier.

"The old rules, if you like, probably no longer apply," he told the Royal Commission into National Natural Disaster Arrangements on Friday.

"You've got to take each season on its merits based on what we're seeing with the changing climatic conditions."

Mr Leach said the bushfire season did not usually occur across Australia at the same time, typically starting in the north and moving progressively south.

The advantage of that was resources could be moved around and reallocated to respond to fires as they occurred in different locations and jurisdictions, he said.

The bushfire season usually starts in northern and central Queensland in August/September and makes its way south over the summer months.

Fires started earlier than usual last year, in July, due to the drier than normal conditions Queensland had experienced.

"Parts of Queensland had experienced several years of drought and that had an effect on drying out the soil and the fuels right across Queensland," Mr Leach said.

The bushfire seasons in the north and south of Western Australia have started to overlap despite their different climates, while the start and end dates for other natural disasters like tropical cyclones are also changing.

"Some of these definitive start and end dates for many of the risks that we face here in Western Australia and possibly across Australia, I would say those lines are being blurred the further on we go," Department of Fire and Emergency Services commissioner Darren Klemm said.

Mr Klemm said the bushfire season in WA's north would start soon and run into October/November, while in the south it traditionally started in December.

But there were significant fires in the south in late October and November last year, while in 2015 the Esperance fires occurred under catastrophic weather conditions in November that year.

"Last season was also one of the first seasons that I can recall where we had an overlapping of the northern and the summer bushfire seasons," Mr Klemm said.

"In late 2019 we were still dealing with fires in the north of the state at the same time that we were commencing the bushfire season in the southern part of the state."

Mr Klemm said fire behaviour had also changed, due to soil moisture deficiencies over time from declining rainfall.

"Certainly we're seeing fire activity at night during the bushfire season in the southwest part of the state that we didn't used to see."

Australian Associated Press