Despite predictions of a wetter spring for much of eastern Australia, southern coastal Queensland received average or below average rainfall during September, prolonging at least 18 months of severe rainfall deficiencies in the region.
This comes after spring rains largely failed last year in southern and eastern Queensland, despite an emphatically wet seasonal forecast.
"There were issues last year around the region not getting typical rainfall that we would have expected during a La Niña year. Now it does look as though that's crept back and we're having round two, unfortunately," said Andrew Watkins, the head of operational services at the Bureau of Meteorology.
Wivenhoe dam levels drop
The dry spell coincides with south-east Queensland's largest reservoir, Wivenhoe, falling to 40 per cent capacity, due to below average rainfall.
This is lower than the same time last year when the dam was 42 per cent full and continues significant decreases over the past three years.
"We're not getting enough rainfall where we need it most ? over our largest and most important dam catchment, Wivenhoe Dam," the dam's operator, Seqwater said in a statement.
South-east Queensland's combined dam levels are currently at 56 per cent capacity ? about 3 per cent less than the same time last year.
Seqwater said last month that water restrictions would likely come into effect in south-east Queensland if the combined total of the region's dams dropped below 50 per cent, which could occur by December.
"With the weather heating up, now is the time for us all to monitor our water use and be water wise," Seqwater said in a statement.
South-east Queensland keeps missing La Niña rain
2020 was not the only year southern coastal Queensland has missed out on rain during La Niña seasons, according to the Bureau of Meteorology's Andrew Watkins.
"2000-2001 and 1988-89 were two La Niña periods where we also saw some dry in that part of the world," he said.
To better understand why southern coastal Queensland missed out on La Niña rain last year, scientists from the Bureau of Meteorology teamed up with researchers from Australian universities to study why climate models have not been accurately predicting the dry weather.
"This forecast error over eastern Australia was an unpleasant surprise to the users of seasonal forecasts, damaging the credibility of seasonal climate forecasts," wrote the team led by Eun-Pa Lim, a Senior Research Scientist at the Bureau of Meteorology in the journal Nature Scientific Reports.
"The study highlights that it's really not as simple as 'La Niña means wet'," said Dr Andrew King from Melbourne University, a co-author of the research.
The team found that other climate drivers, including a pattern of tropical storm activity called the Madden-Julian Oscillation (MJO) acted to suppress rainfall across northern and eastern Australia during November.
The MJO can only be predicted accurately several weeks out, unlike La Niña which can be predicted often months in advance.
"What that means is if the MJO does something weird later on in the season, it is sometimes missed in a seasonal forecast," said Dr King.
"When the model says something with really high confidence that doesn't happen, it's definitely worth interrogating what went wrong," he said.
© ABC 2021
13:38 AEDT A 75-year-old cattle farmer used a jet ski to stage a heroic rescue of a woman stuck in fast-moving floodwaters near the Queensland town of Dalby.