Over 50 sites recorded a metre of rainfall or more in one week during record falls across south-east Queensland and coastal NSW in February/March.
Some regions recorded more than five times their monthly average, the Bureau of Meteorology (BOM) said last week, while others had 2.5 times their monthly average rainfall.
In its Special Climate Statement 76, the Bureau said that after two years of La Niña conditions, the rain fell on saturated catchments leading to flash and riverine flooding extending from Maryborough in Queensland to Grafton in NSW.
In parts of northern NSW, flood levels broke previous records. Wilsons River in Lismore peaked at a record high level, estimated to be 14.4 metres on 28 February. The previous record was 12.27 metres in February 1954.
Some areas of south-eastern Queensland had their highest flood peaks since 1893, though the lower Brisbane and Bremer rivers and Lockyer Creek peaked below the levels of both January 1974 and January 2011 floods.
The rainfall was the result of a combination of weather systems over eastern Australia and the Tasman Sea, where a large volume of humid tropical air moving onshore was lifted into the atmosphere to produce heavy rain and thunderstorms.
In its latest Climate Driver Update, the BOM says the 20221-22 La Niña event continues in the tropical Pacific and that even if it eases, eastern Australia will experience average to above-average winter rainfall.