Monday, October 26, 2009

Flood risk multiplies as the seas rise

Marian Wilkinson in the Sydney Morning Herald (Australia): As John Hunter travels around Australia for the Federal Government advising on climate change, the oceanographer is constantly asked by planners, "How much do we need to allow for sea-level rise?'' He replies, ''What kind of risk do you want to take?''

Dr Hunter was a key witness to the federal parliamentary committee on coastal communities, providing evidence for lay people on understanding sea-level rise. The Intergovernmental Panel on Climate Change puts the projected sea-level rise at up to 80 centimetres by 2100. The rule of thumb is that a one-metre rise will move the shoreline back between 50 and 100 metres.

This is what ocean scientists call the Bruun rule - one centimetre of sea-level rise results in about a metre of coastal recession. But this figure also depends on winds, waves and currents. Dr Hunter told the committee there would also be a disproportionately large increase in the frequency of flooding events from the sea because of higher tides and storm surges.

A sea-level rise of 20 centimetres would increase the frequency of extreme events by a factor of about 10, Dr Hunter said. In other words, these floods and storms will happen 10 times more often. With an increase of 50 centimetres, there will be an average increase of a factor of about 300. "If you have a flooding event which only happens every year at the moment, by the end of the century it will be happening every day.''

The effect on beachfront properties and their owners could be profound. Professor Will Steffen of the Australian National University told the committee: "You may think that a sea-level rise of 20 centimetres or half a metre is not a whole lot, but when you couple it with a wall of water created by a storm coming in at you it leads to a much bigger area of inundation."…

London Arch (aka London Bridge), Great Ocean Road, Victoria Australia. Shot by Jon Hurd, Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 License

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