Climate experts say authorities need to start planning now for a third consecutive La Nina, Australia's first triple whammy for more than half a century.
The Climate Council says the latest forecasts for a 50 per cent chance La Nina could return by spring could create yet more flood disasters.
The Bureau of Meteorology this week declared the La Nina weather system had stalled for now but climate models predict a 50/50 chance it will return in a few months.
The council's research director Simon Bradshaw said La Nina events had already proved costly to many Australian communities.
Dr Bradshaw said a third consecutive La Nina could mean continued above average rainfall on an already saturated east coast.
He said the risk of extreme rainfall and flooding was also increasing with climate change.
"The former Federal government failed to prepare communities for the east coast flooding disaster earlier this year, despite being warned," he said.
"The new Labor government must take steps now to get ahead of another potential summer of increased flood risk for these communities.
"We all hope another La Nina doesn't eventuate but around a 50pc chance - or around double the normal likelihood - should be taken seriously."
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Dr Bradshaw said there were still 80 recommendations of the Royal Commission into National Natural Disaster Arrangements which needed immediate attention.
He said this "must be" a priority for the new government.
"Australia is under-prepared," Dr Bradshaw said.
"Only a very small fraction of disaster spending is committed to preparedness and resilience building.
"We would expect to see a big shift in this ratio to see a much bigger focus on preparedness given the escalating risk of climate-fuelled disasters."
Climate councillor Greg Mullins said with catchments saturated and dams at capacity, another La Nina means we must prepare for more devastating floods.
"It's also a double-edged sword - when the rains eventually stop the prolific growth will inevitably fuel large grass fires across the interior, then bushfires as coastal forests dry out.
"Unprecedented climate driven weather means unprecedented demands on our already stretched emergency services."
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