More La Nina events to bring bigger waves, coastal erosion

Bigger waves could hit NZ. Photo of Porpoise Bay in the South Island / Getty Images

Bigger waves and more coastal erosion will hit Pacific countries like New Zealand as a projected upsurge of severe El Nino and La Nina events brings an increase in storm events, according to a study out today.

The research, published this morning in the journal Nature Geoscience, strengthens our understanding of the impacts of the climate-driven La Nina and El Nino systems, which were not presently factored into studies on future coastal vulnerability that focused mainly on sea level rise.

International researchers from 13 institutions, including Waikato University, gathered data from 48 beaches across three continents and five countries recorded between 1979 and 2012.

They found the coasts of all regions they investigated were affected during either an El Nino or La Nina year, although differently depending on the location and type of climate system.

When the west coast of the US mainland and Canada, Hawaii, and northern Japan felt the coastal impacts of El Nino -- characterised by bigger waves, different wave direction, higher water levels and erosion -- New Zealand and Australia experienced "suppression" such as smaller waves and less erosion.

During La Nina, this pattern flipped and brought the more severe conditions to the Southern Hemisphere.

The study also investigated the coastal response of other climate cycles, such as the Southern Annular Mode, which had impacts at the same time in both hemispheres of the Pacific.

The data revealed that when the Southern Annular Mode trended towards Antarctica, culminating in more powerful storms in the Southern Ocean, wave energy and coastal erosion in New Zealand and Australia increased, as did the wave energy along the west coast of North America.

Other modes of climate variability, such as the Pacific North American pattern, which related to atmospheric circulation in the North Pacific, were linked to coastal impacts that are more tightly restricted to the northern hemisphere.

"Coastlines of the Pacific are particularly dynamic as they are exposed to storm waves generated often thousands of miles away," said study co-author Dr Mitchell Harley, of the University of New South Wales Australia.

"This research is of particular importance as it can help Pacific coastal communities prepare for the effects of changing storm regimes driven by climate oscillations like El Nino and La Nina.

"To help us complete the puzzle, for the next step we would like to look at regions of the Pacific like South America and the Pacific Islands where very limited shoreline data currently exists."

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