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BOM summer outlook: It will pay to check for floods before setting out this summer

Thursday November 25, 2021 - 09:21 AEDT
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With this much rain around many roads will be flooded. Check before heading out and do not drive through flood waters. - ABC

Thanks to the La Niña, finally announced on Tuesday, conditions are expected to be wetter than average for parts of the east coast this summer, according to the Bureau of Meteorology's official summer outlook. 


But with the climate driver to the west, the negative Indian Ocean Dipole, dying out, the centre is expecting a fairly normal summer in terms of rainfall. 


While it might not end up being the wettest summer on record for Australia as a whole, with many catchments around the country already primed, it won't take much to trigger flooding this summer.


"Spring has been wetter than normal and, as a result, soil moisture is high, water storages are full, and we've seen flooding in some areas," says Andrew Watkins, head of the bureau's operational climate services. 


"Any additional rain on our already-wet landscape will increase the flood risk for eastern Australia this summer." 


NSW dam's dramatic turnaround


In New South Wales, the dams are overflowing. 


According to Tony Webber from Water New South Wales, it is a dramatic turnaround in water security from the worst years of the drought. 


"That was only the end of the summer of 2019/2020," he says.  


Many of the dams that were empty or nearly empty are now overflowing. 


"Keepit Dam on the Namoi ? that's now at capacity and spilling into the Namoi River ? was dry for 14 months. Burrendong ? that's at 128 per cent, but fell to 1.5 per cent," Mr Webber says.


The other big turnaround in the past few years has been flow returning to the Darling River, which has now been experiencing connected flow for many months and the Menindee Lakes are at capacity.


"There are releases occurring into the Lower Darling and the anabranch as we speak," Mr Webber says.


The turnaround has certainly been fantastic for water supply but it's obviously not all good news. 


"The flooding is certainly most regrettable and the damage to the crops across many areas of the state at harvest time is quite heartbreaking for not just the farmers but everybody across the region," Mr Webber says.


"But in the longer term, the water security that we will have for communities, for agriculture, for the environment, is probably the best we've seen in at least a decade."  


Keeping up with the flows if this kind of rain keeps up is going to be an ongoing challenge. 


"Given that the majority of these storages that are at or about capacity, it'll just be an ongoing operational pattern that we've been in for weeks, if not months," he says.


"Waiting for a window between the rain events to lower the storage so that we're in a position to try to capture as much of the follow-up rain event on a wet catchment into a dam that's near capacity and releasing into rivers that are very high." 


Murray-Darling Basin awash 


Given that NSW makes up a large proportion of the catchment, it is therefore not a huge surprise that the Murray-Darling Basin is also awash. 


According to the Murray-Darling Basin Authority executive director of river management, Andrew Kremor, the Murray-Darling Basin storages have already surpassed 2016 levels to reach 93 per cent.


"All this extra water in the system means flows into South Australia have also doubled in 12 months," he says.


"This time last year they were around 17GL a day and were around 34GL a few days ago," he said.


[embed datawrapper dams]Flowing on, South Australia's water stores have also seen an increase in inflows this year. 


"Natural inflow from winter rains have been higher this year when compared to the previous three years, largely influenced by high rainfall in July," according to a spokesperson from SA Water. 


SA Water's reservoirs are currently sitting around 73 per cent ? average for this time of year. 


Even more dramatically, Western Australia has also seen a big uptick in its water stores thanks to plenty of winter rain ? up to 62.1 per cent of capacity from just 27.2 per cent last year.


Meanwhile, Victoria has jumped from 67.3 to just over 85 per cent and the Northern Territory saw a decent boost during last year's wet season. 


More to come in Queensland 


Overall, Queensland's water stores are up from 47.6 per cent this time last year to 54.4 per cent and the SEQ water grid is sitting at 55.5 per cent. 


It may be taking a while for catchments to start generating runoff from recent rain but if the outlook comes to fruition this summer those numbers would certainly be expected to rise. 


Aside from the rain, the first cyclone of the season has already burst into being and more than average are expected this year.


High overnight temperatures could also lead to gruelling heatwaves.


Summer fire outlook


Just because it is wet in one region does not prevent fires in another. 


This year's bushfire outlook suggests a below average risk for parts of the NSW coast but above average for the interior. 


High growth following the recent rain is expected to dry out as the summer goes on upping the risk.


Likewise in WA grass growth is up and above average temperatures are also expected to help dry things out. 


As always, a normal fire risk for the rest of the country does not rule out fire. A normal Australian summer has fires.







- ABC

© ABC 2021

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