Weather bureau forecasts more extreme rain events

The magnitude of south east Queensland deluge revealed in Climate Statement.

The Bureau of Meteorology (BoM) expects heavy rainfall events like the one which hit south-east Queensland and northern New South Wales in February–March to become more common.

A Special Climate Statement on the February-March floods said there had been an increase in the regularity and intensity of heavy rainfall events in Australia.

“The intensity of short-duration (hourly) extreme rainfall events has increased by about 10% or more in some regions in recent decades, with larger increases typically observed in the country's north,” the statement said.

“As the climate warms, heavy rainfall events are expected to continue to become more intense.”

Australia's costliest flood

Insurance Council of Australia (ICA) data released in late June showed the east coast flood was Australia’s third costliest extreme weather event behind the Eastern Sydney Hailstorm (1999) and Darwin's Cyclone Tracey (1974).

Updated ICA data showed Australia's costliest flooding event caused $4.8 billion in insured losses.

Insurance Council of Australia CEO Andrew Hall said the scale of the extreme weather event was unprecedented and the cost continued to rise.

"Money is flowing into these devastated communities with $1.5 billion already paid and this number is increasing every day," Mr Hall said.

At the end of June, RACQ had received more than 15,200 insurance claims and paid out nearly $107 million to members.

This included 12,535 property claims and 2,674 motor claims. Click here to read more about RACQ's flood response.

Mr Hall called on Australian governments to implement measures to better protect households and communities from future extreme weather events.

“We also need to plan better so we no longer build homes in harm’s way, make buildings more resilient to the impacts of extreme weather and remove state insurance taxes which only discourage adequate insurance cover,” he said.

Rainfall records smashed

The BoM said several rainfall records were broken during the February–March floods, with more than 50 sites recording more than one metre of rain in a week.

The Brisbane City gauge recorded 792.9 mm from 23–28 February, which was 78% of the annual average, at the current site, of 1011.5 mm.

It recorded 887.0mm for February – 479% of the current site's monthly average of 185.2 mm.

The highest daily total was 228.4 mm on 27 February, a record for any month at the site.

Daily totals of more than 200mm were recorded from 26–28 February. There were only eight previous days with totals above 200 mm, and none were consecutive.

“When compared across the current and former sites, the Brisbane City gauge set records for all periods from three to seven days,” the statement said.

The BoM's Moreton rainfall district, which includes Brisbane, the Gold Coast, Gympie and Kingaroy, had its wettest week since at least 1900 when national gridded rainfall analysis began.

The totals for the Moreton district were comparable with February 1893, which saw three floods along the Brisbane River and Australia's highest daily rainfall total of 907.0 mm at Crohamhurst on the third of that month.

The highest verified seven-day rainfall total for south-east Queensland was 1,334 mm at Upper Springbrook Alert.

Rivers and creeks overflowed

The Brisbane River at Brisbane City peaked on the high tide at 3.85m on 28 February, lower than the peak of 4.46m recorded in January 2011.

The Bremer River reached major flood levels at Ipswich and peaked on the morning of 28 February at 16.72m

These levels were well below the 19.4m reached in January 2011.

However, heavy rainfall across Brisbane and Ipswich led to significant river and creek level rises along smaller creeks and tributaries, leading to extensive and significant flooding.

The Logan River catchment experienced the most significant flooding since January 1974, with multiple locations along the river peaking above levels observed during ex-Tropical Cyclone Debbie in March 2017.

The Logan River at Waterford peaked about 11.15m, the highest level since January 1974 and well above the major flood level of 9m.

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