The accuracy of weather forecasts is in the spotlight again after devastating rains inundated swathes of south-east Queensland and northern New South Wales.
Queensland Premier Annastacia Palaszczuk said that repeatedly changing weather forecasts made it difficult to plan an emergency response.
But while there is a quirk that may have affected the day-to-day accuracy of weather forecasts in the last couple of years, climatologists say it would be unfair to claim the BOM missed the mark on the weekend's floods.
In fact, forecasts in general have been getting more accurate — extreme events are just much harder to predict, and becoming harder still due to climate change.
Is the Bureau of Meteorology becoming less accurate?
Weather forecasts from the BOM have actually been more accurate than they were a decade ago.
The Bureau's next-day temperature forecasts were within 2 degrees Celsius of the actual temperature nine times out of 10 over 2020-21, a result that has been trending up over the past decade.
BOM says its seven-day forecasts today are as good as its four-day forecasts were in the 2000s.
Rainfall is much harder to predict, though last year the BOM also had fewer instances where forecast rain fell outside the accurate range than in the previous four years.
But forecasting for how an extreme weather event will impact a specific area is different to day-to-day predictions.
The BOM's supercomputer churns millions of data points and runs them through several global forecasting models, and for extreme weather brings in local meteorologists with knowledge of the area, as well as incorporating local weather observations to help make its predictions.
Australian National University professor of climatology Janette Lindesay says those models are good at predicting whether there will be a major weather event.
But predicting how it might unfold is much harder.
"Exactly where there is likely to be that heavy rainfall and how much there is likely to be is extremely difficult to predict, because that is dependent on things like wind, what direction it's blowing from, if it changes direction at sea ... what time they make landfall on the coast, the land versus ocean temperatures it's encountering, all sorts of things," Professor Lindesay said.
Weather systems are constantly developing, and change as they pass through changing environments, which also affects how fast and where they move, making timing hard to predict.
On the coast, predictions are made harder still as higher moisture levels in the air bring more energy and make storms more dynamic.
Annastacia Palaszczuk pointed to changing predictions that indicated "on Friday, conditions were easing, and then it changed on Friday, that conditions were going to be easing on Saturday, then they didn't ease, then the conditions were going to be easing on Sunday" as one reason it was hard to prepare for flooding.
Professor Lindesay said that was inevitable.
"The reason these forecasts for this event and any other extreme event change is that basically the circumstances that the system is developing in change," she said.
"Rainfall is very difficult, it is not something you are going to get right 100 per cent of the time — and it's unfortunate but understandable that when you get an extreme event, those are the circumstances when you are most likely not to be correct."
LIVE COVERAGE: Follow flood developments as they happen on the ABC's blogAnd while forecasts changed as the system developed, BOM noted it gave warnings days in advance.
"The Bureau of Meteorology forecast the risk of heavy rainfall for both south-east Queensland and northern New South Wales many days in advance, with flood watches and warnings also issued days in advance," a spokesman said.
"The Bureau continued to update its forecasts and warnings as new information came to hand."
Concerns Bureau of Meteorology understaffed
When the Bureau of Meteorology was subject to a $10 million funding cut over four years from 2014, it said there would be no impact to its services.
Since then its funding has improved, and the Bureau said in a statement that it had not had its funding reduced overall.
But Queensland Labor senator Murray Watt says whether the Bureau is adequately funded will need to be assessed once flood waters recede.
"There have been some issues in recent years around staffing numbers in the Bureau of Meteorology with cuts to staffing and moving staffing around," Senator Watt said on Tuesday.
"And I think that that is something that we do need to have a good look at.
"Right now probably isn't the time to be point scoring and that kind of thing, but I think that there are serious issues about the capacity in those institutions to make sure that we all have the information that we need."
One former BOM employee, who did not work in forecasting or emergency response, told the ABC it was unlikely that staff shortages affected the Bureau's forecasting over the weekend.
He said much of that work was automated, and that forecaster rosters were "pretty defined".
The Community and Public Sector Union noted that despite an overall increase in funding, there were 122 fewer BOM employees last year compared to a decade ago.
"We know that since 2013 over 15 per cent of public service jobs have been cut under successive Liberal governments, causing enormous damage to the capacity of the Commonwealth to deliver policy and essential services that all Australians expect and rely upon," CPSU secretary Melissa Donnelly said.
Grounded planes during COVID-19 might have hurt accuracy
But while the BOM overall has been more accurate than ever, there is one forecasting quirk caused by COVID-19 that may be to blame for some forecasts being off in recent years.
The use of weather balloons has increasingly been replaced by data captured by aircraft instrumentation from commercial flights.
That meant when planes around the world were grounded due to the pandemic, the Bureau of Meteorology lost around 800,000 daily observations to help make its forecasts.
One forecasting agency suggested this could ultimately throw out day-to-day forecasts by as much as 15 per cent, and a 2020 study published in the Journal of Geophysical Research suggested it may have thrown out the BOM's seven-day forecasts by up to 1.5 degrees Celsius.
But while there were fewer observations for the BOM to use, it's not clear whether it ultimately affected the accuracy of forecasting.
BOM maintains that its forecasting was not impacted by the pandemic.
Professor Lindesay said sometimes people just remembered forecasts that weren't accurate, even if those occasions were rare.
"Statistically, that's perfectly acceptable — for an individual person who is experiencing a heatwave, maybe they think that's not sufficient," Professor Lindesay said.
Climate change is making forecasting harder
While the BOM is getting more accurate overall, Professor Lindesay said climate change was making it harder to predict extreme weather events.
The basic physics haven't changed — what has changed is that weather events are happening in places where they never used to, and what has happened in the past has become less useful predicting the future.
Professor Lindesay said for much of the 20th century meteorologists could take a 30-year average of a region's weather to get a good picture of what its climate was like.
While they still do that, rising temperatures have so rapidly changed weather systems and rainfall it has disrupted forecasts.
"We have to be perhaps a bit more cautious about how we use what we understand about how things have worked in the past to predict forecasts about what might happen in the future, because that future is not necessarily going to look the same," Professor Lindesay said.
"And I think that does need to be communicated better."
