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Severe El Niño and La Niña events will cause extreme coastal flooding, erosion

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A multi-agency study has established that severe El Niño and La Niña events will lead to extreme coastal flooding and erosion in populated regions across the Pacific Ocean.

When it comes to coastal vulnerabilities, most of the studies do not take into consideration the impact of El Niño and La Niña; however, the new study that takes into account data from 48 beaches on the Pacific Ocean has shown that the increase in severity of both the events will amplify coastal erosion as well as cause flooding in the areas.

For the study, researchers analysed data from multiple coastal areas from 1979 to 2012. One of the primary things the researchers were looking for was to determine if patterns in coastal change could be connected to major climate cycles.

“This study significantly advances the scientific knowledge of the impacts of El Niño and La Niña,” said Patrick Barnard, USGS coastal geologist and the lead author of the study. “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.”

This is for the firs time that researchers have analysed data from across the Pacific to determine basin-wide patterns. The research group determined all Pacific Ocean regions investigated were affected during either an El Niño or La Niña year.

When the west coast of the U.S. mainland and Canada, Hawaii, and northern Japan felt the coastal impacts of El Niño, characterized by bigger waves, different wave direction, higher water levels and/or erosion, the opposite region in the Southern Hemisphere of New Zealand and Australia experienced “suppression,” such as smaller waves and less erosion. The pattern then generally flips: during La Niña, the Southern Hemisphere experienced more severe conditions.

A co-author of the paper, Professor Andrew Short from the University of Sydney, says forecast increases in the strength of El Niño and La Niña weather events driven by global climate change means coastal erosion on many Australian beaches could be worse than currently predicted based on sea level rise alone.

“Coastlines of the Pacific are particularly dynamic as they are exposed to storm waves generated often thousands of miles away. 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 Niño and La Niña. 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,” said Mitchell Harley of UNSW Australia, and a coauthor of the paper.

“It’s not just El Niño we should be concerned about,” said Ian Walker, professor of Geography at the University of Victoria and coauthor of the study. “Our research shows that severe coastal erosion and flooding can occur along the British Columbia coast during both El Niño and La Niña storm seasons unlike further south in California. We need to prepare not only for this winter, but also what could follow when La Niña comes.”