Severe El Niño events will lead to coastal flooding and erosion

Map courtesy NOAA

The projected upsurge of severe El Niño and La Niña events will cause an increase in storm events leading to extreme coastal flooding and erosion in populated regions across the Pacific Ocean, according to a multi-agency study published Monday in Nature Geoscience.

The impact of these storms is not presently included in most studies on future coastal vulnerability, which look primarily at sea level rise. New research data, from 48 beaches across three continents — including Hawaii — and five countries bordering the Pacific Ocean, suggest the predicted increase will exacerbate coastal erosion irrespective of sea level rise affecting the region.

Researchers from 13 different institutions analyzed coastal data from across the Pacific Ocean basin from 1979 to 2012. The scientists sought to determine if patterns in coastal change could be connected to major climate cycles.

Although previous studies have analyzed coastal impacts at local and regional levels, this is the first to pull together 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.10881697_595527693881949_8814641042094097058_n

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

The published paper, “Coastal vulnerability across the Pacific dominated by El Niño/Southern Oscillation” is available online.

Abstract: To predict future coastal hazards, it is important to quantify any links between climate drivers and spatial patterns of coastal change. However, most studies of future coastal vulnerability do not account for the dynamic components of coastal water levels during storms, notably wave-driven processes, storm surges and seasonal water level anomalies, although these components can add metres to water levels during extreme events. Here we synthesize multi-decadal, co-located data assimilated between 1979 and 2012 that describe wave climate, local water levels and coastal change for 48 beaches throughout the Pacific Ocean basin. We find that observed coastal erosion across the Pacific varies most closely with El Niño/Southern Oscillation, with a smaller influence from the Southern Annular Mode and the Pacific North American pattern. In the northern and southern Pacific Ocean, regional wave and water level anomalies are significantly correlated to a suite of climate indices, particularly during boreal winter; conditions in the northeast Pacific Ocean are often opposite to those in the western and southern Pacific. We conclude that, if projections for an increasing frequency of extreme El Niño and La Niña events over the twenty-first century are confirmed, then populated regions on opposite sides of the Pacific Ocean basin could be alternately exposed to extreme coastal erosion and flooding, independent of sea-level rise.

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