As Brisbane's Wivenhoe Dam begins lowering its water level ahead of the flood season, a Bureau of Meteorology forecaster explains why Queensland's summer will be different from the one that sparked devastating floods in January.
Earlier this month the Queensland Government announced it would lower the water level of the dam supplying Brisbane from 80 per cent to 75 per cent on advice from the weather bureau.
The bureau is predicting Brisbane and parts of south-east Queensland will have a 70 to 75 per cent chance of above-average rainfall between November and January, similar to what was predicted last year.
It also says the La Nina weather event, which brings with it conditions for high levels of rain, is back.
So why is this summer predicted to be different from the conditions which caused January's historic floods?
BOM manager of climate prediction services Dr Andrew Watkins says while people may draw conclusions from this year's rainfall prediction, all the extreme weather factors of last year are not lined up again this year.
"On first inspection you might say we've got similar probabilities, we might have a similar year to last year... but the reality is our model this year is being driven a lot by what is happening in the Indian Ocean," he said.
"Last year it was driven a lot by what was happening in the Pacific Ocean."
Dr Watkins says ocean temperature data has shown this year's La Nina event is weaker than last year.
“Basically during a La Nina you tend to have warmer water over towards Australia and cooler water over to South America, and where you get the warmer water tends to be where things evaporate more and you get more cloud formation and humidity and so on," he said.
"And when those warmer waters are near Australia you get a greater chance of good rainfall because you’ve got more moisture floating around the atmosphere.
"When you have an El Nino you tend to have cooler water near Australia and warmer water near South America."
Dr Watkins says temperatures in the Pacific Ocean were about 1.5 degrees cooler than normal last year, while this year they are only 0.8 degrees cooler, leading to a relatively weak La Nina.
He says at this time last year, ocean temperatures in the north of Australia were at record levels but this year they are close to average.
"And last year we also had an Indian Ocean that was very favourable for rainfall as well, particularly in the tropics," he said.
"This year our tropical Indian Ocean isn't quite as favourable for rainfall as last year."
Dr Watkins says the Southern Oscillation Index (SOI), which is another measure of a La Nina, measured 20 to 25 at this time last year but is only at 8 to 10 this year.
"This year the La Nina is quite weak whereas last year it was a very strong event," he said.
"What we've seen last year we've only really seen two or three of that strength since 1900."
Dr Watkins says La Ninas and El Ninos tend to form in the late Australian autumn or early winter, as it did last year.
But he says this year's La Nina formed in mid-to-late spring.
"For one to form after the end of winter is not unheard of, but it is a lot later in the year to be occurring than one that is fairly typical," he said.
"To some degree that is contributing to why that is a relatively weak event compared to ones in the past.
"It would have had to build up very quickly to reach anywhere near the strength that we saw last year."
Dr Watkins says even though the La Nina formed late, it does not mean it will continue on longer into the new year.
"Our seasonal cycle simply means that La Ninas and El Ninos will start to break down. They struggle to survive through an autumn period," he said.
"Typical for a La Nina event, like we saw last year rather than this year, they peak in about December or January and they start to weaken. Then by about May they typically are gone.
"The model forecast that we see at the moment tends to suggest we could start to see it peak in December or even into early January as well, so there's no suggestion at the moment that it's going to continue on for anything other than the normal period."
Dr Watkins expects that while there may be above-average rain, the extremes that fell into place last year are not here this year.
"Last year we had the Pacific, Indian and northern Australian factors all lined up in a row, and if it hadn't have rained buckets we really would have been scratching our heads," he said.
"This year all those conditions are weaker than last year, and hence even though we're in a La Nina and even though the map does indeed suggest above-average rainfall through south-east Queensland, as to whether it would be the extreme event of last year, the odds are reduced of that.
"It's not as likely that you would see as extreme rainfall as you did last year because those factors aren't all lined up as they were last year.
"So the factors are there to suggest above-average [rainfall], but the factors aren't there to suggest extremes in the climate."
But Dr Watkins warns that while Queensland as a whole may not see rainfall and flooding like in January, there are still dangers.
"[The La Nina] has formed late and it is quite a lot weaker than the one we saw last year, but during any La Nina event it won't surprise us if there are individual areas that do get extremes like last year," he said.
"But when you consider over the wide scale over all of south-east Queensland, the odds aren't as high as last year of getting those extremes."
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