SYDNEY — Devastating flooding is ongoing across Australia, where an area the size of Alaska with some 10 million people is at risk for excessive rainfall and storminess. The flooding comes amid colliding weather systems gripping the country. Up to 35 inches of rain fell in just four days, and some places are seeing their worst flooding in 60 years.

Nearly three times the average March rainfall has fallen in a number of locales, which Australia’s Bureau of Meteorology described as “phenomenal,” with additional rain and flooding expected in the days ahead.

Hardest hit has been eastern Australia, including Sydney and New South Wales, areas afflicted by rampant wildfires in late 2019 into 2020. Over 10 million acres burned and dozens died in the blazes.

“I don’t know any time in state history where we have had these extreme weather conditions in such quick succession in the middle of a pandemic,” New South Wales Premier Gladys Berejiklian told reporters.

Now, more than 18,000 people have been evacuated in response to what the Bureau of Meteorology is describing as a “volatile, dangerous and dynamic” weather situation.

Excessive rainfall from converging weather systems

Most of eastern New South Wales and southeast Queensland has seen four inches or more of rainfall since late last week, with many locales picking up a great deal more:

  • Comboyne, about 150 miles northeast of Sydney on the Mid North Coast, had received a staggering 35 inches by Monday morning local time. Sydney itself had its wettest day of the year Sunday with 4.4 inches.
  • Minnie Water, about 125 miles south of Brisbane in New South Wales, had seen more than 10 inches of rain since between 9 a.m. local time Monday and midnight. Nambucca Heads, just to the south, had tallied 9.6 inches, while nearby Woolgoolga saw 7.2 inches.

Reuters reported the flooding in Sydney’s western regions was the worst since 1961.

The floods come at the end of a wetter-than-average summer, with dams and catchments at close to capacity.

The relentless deluges stem from a trio of weather systems steering ashore a fire hose of moisture. A tropical low north of Western Australia has contributed to a deep stream of moisture, while an equator-ward meandering of the jet stream, east of Queensland and New South Wales, has helped draw that tongue of moisture all the way to the coast.

Farther southeast, high pressure over the Tasman Sea between southeast Australia and New Zealand has contributed to even more moisture being drawn onto land, sparking continuous downpours near the coast.

That same combination of weather systems is leading to strong onshore winds gusting near 50 mph, resulting in coastal flooding.

“Water levels could exceed the highest tide of the year during Tuesday morning’s high tide as a storm surge moves into coastal areas,” wrote the Bureau of Meteorology.

Flood warnings blanket the map in eastern Australia, where the rainfall has poured into area rivers and sparked serious inundations. Complicating matters are the burn scars from the summer’s record-shattering wildfire season, which are particularly susceptible to periods of excessive rainfall and runoff. That boosts the risk of landslides.

“Super-saturated soil along areas of the east bring an increased risk of moderately gusty winds toppling trees,” wrote the Bureau. “Heavy rain, likely leading to flash flooding, presents a serious risk to the Northern Rivers and Mid North Coast today [Monday] and on Tuesday. In some areas, heavy rain and flooding may be life-threatening.”

The threat for heavy rainfall will diminish markedly as a front drives storms offshore by early Wednesday, ushering a cooler and drier air mass to clear the atmosphere. A risk for flooding will remain, particularly along elevated rivers that overflowed their banks during the weekend.

Toll of flooding linked to poor preparedness

The Associated Press reported that the floodwaters had isolated 35 communities in New South Wales and that emergency services had conducted more than 700 rescues.

Experts have warned of the likelihood for a flood catastrophe of this magnitude for years. Scientists and urban planners pointed to successive governments approving the construction of more houses in flood-prone areas during an era of shifting climate.

“The impact of the floods in the Hawkesbury-Nepean valley is due to poor governance rather than any act of God,” said Jamie Pittock, a professor from the Fenner School of Environment & Society at the Australian National University. “Extreme floods have been recorded in the valley since the earliest years of British occupation over two centuries ago. And now climate change is likely to increase the frequency of dangerous floods.”

Dorina Pojani, a senior lecturer in urban planning at the University of Queensland, said the “obvious suggestion” is that housing shouldn’t be permitted in areas at risk of flooding, in the same way that some of the catastrophic damage from recent wildfires could have been avoided had residential construction not expanded into previously natural areas.

“As a society, we have been very arrogant to think that we can dominate and subjugate nature without suffering any consequences,” she said.

Australia may have to embrace the architectural concepts of water-based cultures in Southeast Asia, adopting floating housing and housing on stilts, which can cope better with floods, Pojani added. That style of building — where houses are raised above the ground on stilts or stumps — is common in tropical Queensland state, but not around the Sydney area.

The flooding hasn’t just impacted people. Stranded livestock has been rescued from floodwaters, while a variety of smaller critters, such as insects and arachnids, including tarantulas, have sought refuge atop vegetation, on homes and in garages.

The Bureau of Meteorology issued a formal warning to sheep grazers, stating “there is a risk of losses of lambs and sheep exposed to these conditions.”

Climate change worsening Australia’s weather extremes

The devastating floods come a little over a year after one of Australia’s worst fires seasons on record. The fires emitted so much smoke into the atmosphere that they slightly cooled the entire planet, impacting the climate not unlike a moderate volcanic eruption.

The explosive blazes formed violent fire-induced thunderclouds, shot smoke 19 miles into the sky and formed plumes that circumnavigated the globe. The fires came amid a multiyear drought and record-breaking heat, which scientists said were intensified by climate change. Now, some of the some regions that were engulfed by flames are engulfed by floodwaters, and climate change may again be making the situation worse.

By speeding up evaporation, a warming climate can exacerbate weather patterns that lend themselves to both extreme dryness and excessive rainfall. In dry regimes, the land surface loses water more quickly and heats up, transforming it into a tinderbox for rapidly spreading fires. When it’s wet, the faster evaporation puts more water into the atmosphere, which can be unleashed in torrential downpours.

Cappucci and Samenow reported from Washington.