The Bureau of Meteorology today issued a La Nina alert, confirming the chance of the flood-inducing weather system occurring this year has risen to 70% – about three times the normal likelihood.

Manager of Climate Operations Andrew Watkins says La Nina typically results in above-average winter-spring rainfall for Australia, particularly across eastern, central and northern regions.

“It typically also brings cooler and cloudier days, more tropical cyclones, and an earlier onset of the first rains of the wet season across the north,” Dr Watkins said.

The cooling of surface temperatures in the tropical Pacific Ocean and an increase in the strength of the Pacific Trade Winds are clear indications the chance of La Nina has risen, the Bureau says.

“When these two changes occur at the same time, at this time of year, we see a greatly increased chance of a La Nina forming and persisting through spring,” Dr Watkins said.

“Climate models suggest that further ocean cooling and intensification of Trade Winds may occur over the coming months, which has triggered the Bureau to shift from a La Nina Watch, issued on 26 June, to a La Nina Alert.”

The last significant La Nina event was in 2010-11, which was Australia’s wettest two-year period on record. Devastating flooding in Brisbane and other parts of Queensland resulted in insured losses of more than $1.5 billion.

Bureau background documents confirm the presence of La Nina “increases the chance of widespread flooding”.

“Of the 18 La Nina events since 1900 (including multi-year events), 12 have resulted in floods for some parts of Australia, with the east coast experiencing twice as many severe floods during La Nina years than El Nino years,” the Bureau says.