How a marine heatwave caused a terrifying Queensland deluge

The heavy rain that drenched the north Queensland coastline over the weekend reached up to 1.5 metres over three days in some places – more than a year’s worth of rain by Sydney standards and more than two years for Melbourne.

The torrential downpour was likely to have been exacerbated by climate change, scientists linking it to a prolonged marine heatwave in the Coral Sea.

The rain is finally easing off and the weather bureau has cancelled the severe weather warning for the region on Tuesday morning, though swollen rivers remain a danger and thunderstorms could bring localised heavy rainfall over the next few days.

A flooded substation in Ingham on Monday.Credit: Ergon Energy

The Herbert, Burdekin and Haughton rivers are all in major flood, while Ross River is in moderate flood.

Bureau of Meteorology senior meteorologist Jonathan How said many parts of the region from Ayr to Cairns had more than one metre of rain – more than they usually receive in six months – in the 72 hours from 9am Friday to 9am Monday.

“The highest was at a place called Rollingstone – they’ve seen 1475 millimetres in three days, and we have seen another number of other locations crack 1000 millimetres,” How said.

Weather bureau records show the rain eased in the 24 hours to 9am Tuesday, though was still heavy by regular standards – Rollingstone received 97 millimetres over this time-frame.

How said average annual rainfall varied from 1100-1200 millimetres in Townsville to 2000-2500 millimetres north of Ingham, with most of it falling in the summer. Rainfall for earlier in the summer was average to above average.

For comparison, Melbourne Olympic Park has an average annual rainfall of 579.7 millimetres, while Sydney Observatory Hill has average annual rainfall of 1211.1 millimetres.

Even by the standard of wet season in the tropics, this was an extreme level of rainfall.

Steve Turton, adjunct professor of environmental geography at CQUniversity Australia, wrote in The Conversation that it fit with the broader trend of climate change.

“More extreme rainfall and higher frequencies of flooded rivers and flashfloods around the world have a clear link to climate change and ongoing global heating,” he said.

Flooded land near Proserpine on Monday.Credit: CQ Rescue

Turton said there was an increasing trend for tropical lows to stall, “sitting in place over or near land and dumping huge volumes of rain”. This trend was noticeable in the current flooding rain event and also the 2019 Townsville floods and the 2023 Cairns and Daintree floods.

For every degree of warming, the atmosphere can hold 7 per cent more moisture, according to the laws of thermodynamics. That makes humid weather more common and also increases the prevalence of heavy rainfall events because it means there is more water in the atmosphere that will eventually fall as rain.

Hotter oceans also hold more energy, Turton said, meaning they can also amplify the global water cycle when atmospheric conditions are suitable.

Scientia Professor Matthew England, a climate scientist at the University of NSW, said global ocean temperatures have risen by more than one degree, which meant a much more humid atmosphere.

“We know with absolute certainty that warmer oceans evaporate more moisture into the atmosphere, and we know that that loads the chances of heavier rainfall events,” England said.

“These sort of catastrophic flooding rains you’re seeing around the world are linked to warmer ocean temperatures, and it’s a natural consequence of global warming.”

England was involved in previous research that found that climate change had made the catastrophic 2011 Brisbane floods three times more likely, when the seasonal effect of a La Nina climate system was stripped out.

England said an attribution study that would prove a link to climate change had not yet been done for the north Queensland floods. However, he said temperatures in the Coral Sea, next to where the flooding rains were occurring, were 1-2 degrees warmer than average in the lead-up.

These days attribution studies are being turned around quickly. World Weather Attribution has already done a rapid scientific analysis of the Los Angeles fires and found they were significantly worsened by climate change.

The 32 scientists from the United States and Europe found human-caused climate change worsened the ferocious Los Angeles wildfires by reducing rainfall, drying out vegetation and increasing the overlap between flammable drought conditions and strong Santa Ana winds.

The hot, dry and windy conditions that drove the fires were about 35 per cent more likely due to warming caused primarily by the burning of oil, gas and coal. Such conditions will become a further 35 per cent more likely if warming reaches 2.6 degrees, which is forecast by 2100 unless emissions are cut rapidly.

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