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Global warming warning after ChCh floods

Thursday 6 Mar 2014 5:50 p.m.

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The Christchurch flood is being called a one in 100 year event but scientists are warning rising sea levels will make coastal flooding much more common.

Climate change is expected to raise the seas by up to a metre in the next century potentially putting tens of thousands of coastal homeowners at risk.

It took just hours for the water levels to rise but there's another water level rise happening - more slowly - but with long term effects and it's caused by global warming.

The flooding was primarily caused by torrential rain, but University of Canterbury coastal studies lecturer Deirdre Hart says sea levels also played a part.

Rob Bell of NIWA says seas around New Zealand are expected to rise between 70cm and a metre in the next century.

"Our future generations and also our younger generations are going to increasingly experience coastal flooding, it's going to become more frequent and then they're going to have to make some decisions about retreating from the coast," he says.

Mr Bell says around 100,000 people in New Zealand live up to only three metres above current sea level - and they will be most vulnerable to a rise.

Properties on one beach just north of Thames suffered extensive flooding in 2005. Like Christchurch that was described as a one in 100 year event. But if sea levels rise, the time frame shortens.

"Half a metre of sea level rise, instead of that sort of event happening every 100 or 200 years, you'll get them every big tide which will be several times a year," says coastal scientist Jim Dahm.

Ms Hart says Christchurch is a good model of how sea level rise might affect New Zealand because much of the city sunk in the earthquakes.

It's a grim outlook and Mr Dahm says there are only two options - stop climate change or adapt.

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