Sports fields, car parks and parklands will be important assets; houses will have walls that open, and some people might need to lose their water views to prepare for bigger, more frequent floods due to global warming, according to experts contacted by the Herald.
As global temperatures rise, short storm bursts will increase in frequency and severity, resulting in more flash flooding, especially in urban areas. But the outlook for longer periods of extreme rain, such as those that caused the flooding of the Darling, Lachlan and Murrumbidgee rivers, and which made the Warragamba Dam overflow this year, is less certain.
There is consensus in the scientific literature that ”the flooding that happens on small urban type of catchments, which is a result of short rainfall bursts, is going up, because convection is intensifying”, Professor Ashish Sharma, an Australian Research Council future fellow in the school of civil and environmental engineering at the University of NSW, said.
He said it was ”99 per cent sure” that the cause was global warming. A warmer atmosphere holds more water and releases it in shorter bursts, as seen in the tropics, Professor Sharma said.
But modelling of longer duration rain events of 24 hours or more has turned up no conclusive trends, Professor Sharma said, though forecasting models are improving because more people are working on them and increased computing power helps cope with more variables.
What scientists agree on is that the assumption the future climate will mirror the past, known among scientists as ”stationarity”, no longer holds. This has implications for flood planning.
”This represents a major break with past practice”, Seth Westra, a senior lecturer in the school of civil, environmental and mining engineering at the University of Adelaide, said.
”The notion that the climatic drivers of flooding are changing through time not only poses profound challenges on how we estimate future floods, but also challenges the way we design [for] and manage future floods,” he said in a paper written for the federal government-funded National Climate Change Adaptation Research Facility.
Sydney University catchment management expert Willem Vervoort said flexibility in planning was crucial. Towns and cities need to create useable spaces within the landscape which could also be used for floodwater storage when needed.
Sports fields, parks and cycleways along creeks and rivers can be used in dry times and become flood sinks in wet periods, he said. But creating green corridors along creeks and rivers could be difficult because ”maybe people are losing some water views”, such as along Cooks River and in river cities like Coffs Harbour.
The Brisbane architect, Michael Rayner, principal of Cox Rayner Architects whose home was inundated last year’s Brisbane floods, said all of south Brisbane was on a flood plain. With massive population growth forecast for the city, ”we should be looking at the slopes not the plains”, he said.
