UP TO a quarter of a million homes around the country, vital power stations, ports, sewerage pipes, water supplies and transport hubs, including Sydney Airport, are at serious risk of flooding as a result of sea level rise and increased storm tides caused by climate change, the first national assessment of the coastline by the Rudd Government warns.
The report, Climate Change Risks to Australia's Coast, draws on extensive scientific advice and modelling, and will be released today by Climate Change Minister Penny Wong.
It finds homes in NSW have the greatest exposure to risk. Up to 62,400 existing coastal homes in the state valued up to $18.7 billion will be potentially threatened by 2100, although some could feel the impact far sooner.
"This report is the first continental-scale mapping of residential buildings at risk from climate change, and the worrying implications for coastal homes and infrastructure are there for all to see," Senator Wong said.
Lake Macquarie is the most vulnerable region in NSW, with between 5100 and 6800 buildings or about 10 per cent of all residential buildings predicted to be at risk of flooding by 2100.
It is closely followed by the Central Coast cities of Wyong and Gosford, then Wollongong and the Shoalhaven in the south and Rockdale at Botany Bay.
The report draws on scientific experts from the CSIRO, GeoScience Australia, the University of Tasmania and the Department of Climate Change. It reinforces warnings from the recent parliamentary committee report and the NSW Governments sea level rise policy.
While the parliamentary report put an estimated 200,000 buildings at potential risk in NSW, this report uses mapping and modelling to focus on the number of residential properties at most risk.
Projected sea level rise is estimated to reach around 90 centimetres by 2100.
But the report finds: "There is an increasing recognition that sea level rise of up to a metre or more this century is plausible."
The erosion impact of one centimetre of sea level rise is roughly considered to be around one metre. The report says that with a sea level rise of just 50 centimetres, flooding events that now happen every 10 years would happen about every 10 days by 2100.
The current one-in-100-year flood event could occur several times a year.
Professor Bruce Thom, a key adviser on the report, said that the coastal zone was settled and built up in a "comfort zone" with no expectation sea levels would rise.
He said sea level rises, high tides and storms would combine to allow water to move much higher than was ever expected when coastal areas were developed.
"The elevation of the tides will progressively increase over time and as they do, they'll penetrate into low lying land which is settled or where there's infrastructure . . . the frequency of high tidal flooding will increase from once per year to as much as every tide," he said.
"I call it the Venice effect."
Sea level rises will make problems more acute in towns built on rivers and lakes when floodwaters coincide with tidal waters made higher by rising sea levels, the report says.
When Newcastle had flash floods in 2007 in the storm that beached the Pasha Bulker, water depths reached 1.8 metres, 5000 cars were destroyed and 10,000 properties inundated. It could have been a lot worse.
"Fortunately the peak rainfall event in Newcastle in 2007 coincided with low tidal conditions so there was not also the flooding impact associated with a storm surge," the report says.
"The same event, one week either side, would have resulted in far worse flooding throughout the low-lying suburbs around the harbour."
Professor Thom stressed the report was a first attempt to assess the impact of climate change and the methodology was not perfect and would be refined in later updates.
He also defended the use of a 1.1-metre sea level rise assumption in the report when many other estimates were 10 or 20 centimetres lower.
"My personal view is we can hope for the best but we have to plan for the worst," he said. "The science is pointing in this direction so we cannot avoid planning for it."
Dykes, seawalls and other barriers may have to be built to save coastal properties including many in Sydney and Melbourne, the study predicts..
A dyke across the entrance to Port Phillip Bay is raised as one possible defence for Melbourne although the report warns it would be challenging and very expensive to construct as it would need to be three kilometres long and built in water 20 metres deep. SMH
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