The deluge in Victoria, New South Wales and the island state of Tasmania comes six months after east coast flooding disaster killed 20 people.
Australian authorities have announced the first death from days of widespread flash flooding on Saturday, despite flood levels topping out across much of the southeast.
Hundreds of homeowners began a long clean-up after storm waters engulfed streets, houses and cars across three states, with Melbourne suburbs among the worst hit.
Two very wet years have left much of eastern Australia sodden, and floods now frequently follow even moderate downpours.
“It was frightening. I’ve been here for the other floods but I’ve never seen anything like that,” 61-year-old Antoinette Besalino told AFP news agency.
Areas of three southeastern states – Victoria, New South Wales and the island state of Tasmania – are under emergency flood warnings after an intense weather system this week brought more than a month’s worth of rain to the southeast.
The crisis comes after flooding in March and April on the east coast resulted in A$4.8 billion ($3.3bn) in insured damage, according to the Insurance Council of Australia.
The apparent flooding victim was a 71-year-old man who was “found deceased in floodwaters in the back yard” of his property in the town of Rochester, a small town north of Melbourne.
“Crews are on scene and police are attempting to get to the property, which is currently blocked off due to floodwater,” police said.
“The exact circumstances surrounding the death are yet to be determined.”
As the waters subsided, residents were left wading through mud-caked streets, passing abandoned cars, tree branches festooned with debris and, in one instance, a marooned wheely bin.
“The clean-up is going to be huge,” said 58-year-old Peter Dimauro according to AFP news agency.
“Think about all of the branches and all of the garbage that has washed up.”
About 466 homes have “above-the-floor flooding”, according to Victoria state Premier Dan Andrews.
“Almost certainly those numbers will grow as we see flood waters peak in a number of communities,” he said.
For some, the risk is not yet over, with water still funnelling into already-swollen catchments.
Evacuation orders remain in place for dozens of communities.
“This is serious, this is potentially very, very dangerous,” said Andrews.
Why is it happening?
Australia is exposed, for a third straight year, to the La Nina weather phenomenon in the Pacific Ocean, which typically brings above-average rainfall to the country’s east.
A second contributor is the Indian Ocean Dipole – a climate phenomenon that affects rainfall patterns near the Indian Ocean, including Australia.
It turned negative in May, increasing the chances of above-average rainfall for most of Australia in the September-November spring.
“The oceans north of Australia are warmer and that causes more moisture flowing from the Indian Ocean to eastern parts of Australia,” said Agus Santoso, senior researcher at the University of New South Wales Climate Change Research Centre, according to Reuters news agency.
Compounding the situation were storm cells that brought recent heavy rains to the nation’s east, he said.
“You have basically bad weather, storm and rain systems.”
The Bureau of Meteorology has warned of more widespread flooding for eastern and northern Australia during the nation’s severe weather season, which runs from October to April.
The east coast flooding disaster in March, caused by heavy storms in Queensland and New South Wales, killed more than 20 people.