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New study shows events like Sydney's March 2021 floods could be 80 per cent more likely by end of the century

Friday November 12, 2021 - 20:47 AEDT
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Sydney and much of NSW suffered damaging floods during a prolonged rain event in March. - ABC

After a thoroughly soggy week, a new paper confirms this kind of thing is expected to become more likely as the climate warms. 


What will this mean for low-lying areas and how do we make our communities more resilient to flooding?


PhD student Kimberley Reid studies atmospheric rivers, a emotive name for a narrow region of strong water vapour that streams through the atmosphere. 


These atmospheric rivers allow moisture to flow around the world, and are often associated with heavy rain and floods. 


Incidentally, this week's rain is the result of an atmospheric river but it's not the only one to have hit the country this year.


There was also an atmospheric river during the devastating flooding in Sydney and much of New South Wales in March. 


In a new peer-reviewed study, Ms Reid and her colleagues used climate models to see how frequent events like the prolonged heavy rainfall and flooding in Sydney, would be under moderate and high emissions scenarios.


"So we looked at events that had this long-term water-vapour transport, and found that these kinds of events were likely to occur about 80 per cent more often by the end of the century, under both emissions scenarios."


The moderate emissions scenario (SSP245 for any climate buffs out there) is projected to result in 2.5 to 3 degrees Celsius of warming by 2100 and the high emissions scenario (SSP585) 5 degrees of warming. 


Why would atmospheric rivers become more likely? 


According to Ms Reid, there is a pretty simple explanation for why atmospheric rivers and water-vapour transport would become more common in a warming climate. 


"A warm atmosphere can hold more water, so the chances of getting regions in the atmosphere with this high water-vapour content increases," she said. 


It does not mean that all regions will see more rain, but overall flooding is expected to increase.


Prior to COP26 Glasgow, the UN warned the world was on track to warm by 2.7C by 2100 and a study from the Climate Action Tracker found, despite pledges made at COP26, the world was heading for 2.4C of warming by 2100. 


It's a concern for Ms Reid, as they put warming very close to the scenarios in her study. 


"The main point is that we really need these COP pledges to turn into action if we want to avoid more of these kinds of events in the future," she warned.


Increased flooding has long been linked to climate change


Hamish McGowan from the University of Queensland, not involved with the study, said the new paper reaffirmed what had been evident in the literature for some time now.


"That is, as temperatures warm, the atmosphere's water holding capacity increases and when it rains we get more rainfall," Professor McGowan said. 


"Certainly, this paper makes a valuable contribution in bringing that into a local context by focusing on the event in March in Sydney."


As we moved forward, he said, Australians needed to be conscious of the fact that the climate was going to become more extreme.


"Residents generally need to be conscious of that, but also those who have responsibilities for planning and managing our urban infrastructure.


"That's something certainly which they need to take on board, in terms of how they plan our cities, in preparation for a future where climate and the hydrological system is going to become more variable and at times more extreme."


How do we cope with more flooding? 


According to Richard Thornton, CEO of Natural Hazards Research Australia, if flooding becomes more frequent, it will cease to be a one-off and become something we need to prepare for more thoroughly. 


He recommends checking in with your local council to see if you are in a flood zone, coming up with a plan for how you will respond in a flood and checking you are sufficiently insured. 


He said it was almost a universal mantra for living in Australia these days.  


"Whether it's cyclones, floods, fires, earthquakes all of those things, we need to be more prepared for them because they'll happen one day.


Dr Thornton said it we couldn't contain climate change to something which we could reasonably adapt to, we might need to think about a retreat from certain areas where we currently live.


Moving out of the flood zone is even a possibility, as demonstrated by moving the town of Grantham after the 2011 Queensland floods. 


"We need to think in a really whole-of-community sense about how do we manage the retreat from some of these events," he said. 







- ABC

© ABC 2021

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