22 Sep 2015

Climate events put NZ coast at risk

7:00 am on 22 September 2015

An international study suggests New Zealand's coastlines could be harder hit by climate patterns than scientists previously thought.

Waves crash over the breakwater at Port Taranaki.

Coastal impacts from La Niña could be worsened by rising ocean levels. Photo: RNZ / Robin Martin

Researchers analysed data from 48 beaches bordering the Pacific Ocean from 1979 to 2012 to see whether patterns in coastal change were related to major climate cycles such as El Niño and its counterpart, La Niña.

La Niña is related to the cooling of surface ocean waters along the tropical west coast of South America. The El Niño weather pattern, expected to hit New Zealand this summer, is characterised by unusually warm ocean temperatures in the equatorial region of the Pacific Ocean.

The researchers from 13 institutions, including the University of Waikato, discovered that during periods of La Niña many stretches of New Zealand's coast had to cope with powerful waves and erosion.

Lead author Patrick Barnard from the US Geological Survey said New Zealand could have more coastal damage than in earlier years.

"More extreme La Niñas in the 21st century, as projected by recent global climate models, suggest New Zealand could experience more extreme coastal impacts during La Niña events than recently experienced, which would be even more amplified by global sea level rise."

He said this research would be helpful in future weather events.

"Understanding the effects of severe storms fueled by El Niño or La Niña helps coastal managers prepare communities for the expected erosion and flooding associated with this climate cycle."

The research group found that all the regions in the study were affected during either weather pattern.

When the west coast of the US mainland and Canada, Hawaii, and northern Japan felt the coastal impacts of El Niño, including bigger waves, higher water levels and erosion, the opposite region in the Southern Hemisphere of New Zealand and Australia experienced 'suppression,' such as smaller waves and less erosion, the study said.

The pattern then generally flipped; during La Niña, the Southern Hemisphere experienced more severe conditions.

Ocean erosion threatens the coastal route.

Sea damage to a cliff in the South Island (file photo) Photo: RNZ

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