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article imageEl Niño and La Niña will intensify coastal hazards across Pacific

By Karen Graham     Sep 22, 2015 in Environment
El Nino and La Nina climate circulation events are predicted to become more severe, causing an increase in the number and intensity of storms, leading to extreme coastal erosion and flooding, says a multi-agency study.
The impact from storms associated with El Nino and La Nina oscillation cycles can be seen along the Pacific Coast of North America from southern California to British Columbia and northward. If we look at the entire Pacific Basin, the impact of these circulation events is even more dramatic.
Patrick Barnard, the USGS coastal geologist and the lead author of the study, says, “This study significantly advances the scientific knowledge of the impacts of El Niño and La Niña." The multi-agency research project included scientists from 13 different institutions, including the U.S. Geological Survey, University of Sydney, the University of New South Wales and the University of Waikato (New Zealand).
Severe bluff erosion  along the southern end of Ocean Beach  San Francisco  California  including da...
Severe bluff erosion, along the southern end of Ocean Beach, San Francisco, California, including damage to the guard rail of the Great Highway (Calif. Hwy.1). The severe winter erosion led to lane closures of the highway and an emergency, $5 million revetment along the base of this bluff.
Jeff Hansen/USGF
“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, " said Barnard. He explained that previous studies of these storms have not included coastal vulnerability, almost always focusing on sea level rise.
Science News Online reports that the new research covers 48 beaches on three continents and five countries that border the Pacific Ocean. Barnard says the study suggests that the predicted increase in the severity of storms will also intensify coastal erosion, regardless of any sea level rise.
Coastal data covering the years 1979 to 2012, from all across the Pacific basin was analysed, with the scientists attempting to determine if patterns in coastal changes could be connected to major climate cycles. Data that came from beaches on the mainland United States and Canada, Japan, Australia, New Zealand and Hawaii was used in the study.
Severe coastal bluff erosion  along the southern end of Ocean Beach  San Francisco  California. This...
Severe coastal bluff erosion, along the southern end of Ocean Beach, San Francisco, California. This storm damage occurred during the 2009-2010 El Niño, which, on average, eroded the shoreline 55 meters that winter.
Jeff Hansen /USGS
Researchers found that all Pacific basin regions included in the study have been affected by either an El Nino or La Nina event. The west coast of the U.S. mainland and Canada, Hawaii, and northern Japan all felt the effects of El Nino, with higher water levels and erosion, bigger waves, and waves moving in different directions.
In the Southern Hemisphere, Australia and New Zealand experienced what the researchers called "suppression." This included smaller waves and less erosion. But when La Nina was in force, things were reversed, with the Southern Hemisphere countries seeing higher waves, more erosion and differing wave direction, while on the west coast of the U.S., Canada, Hawaii and Japan, the waves and erosion quieted.
The Southern Annular Mode (SAM)
The study also investigated the effects on coastal areas and their response to other climate cycles, like The Southern Annular Mode, also known as the Antarctic Oscillation (AAO). The best way to describe the SAM would be to say it is the north-south movement of the westerly wind belt that encircles Antarctica. This belt of wind dominates the mid to higher latitudes of the Southern Hemisphere.
When the westerly wind belt expands  more (or stronger) fronts can come closer to southern Australia...
When the westerly wind belt expands, more (or stronger) fronts can come closer to southern Australia. Negative SAM increases the likelihood of above average winter rainfall in southern Victoria.
Government of Australia
Depending on which way the SAM trends, it will result in increased wave action and erosion on the New Zealand and Australian coasts. Another climate variable studied was the Pacific North American pattern. This pattern of atmospheric circulation over the North Pacific is linked to coastal impacts restricted to the Northern Hemisphere.
Trying to link erosion along our coasts to natural climate events like El Nino and La Nina can be challenging. “Shoreline behavior can be controlled by so many different factors, both locally and regionally, that it’s been difficult to isolate the signal until now. However, utilizing the many years of data we were able pull together in this study enabled us to definitively identify how the major climate drivers affect coastal hazards across the Pacific,” said Barnard. “This will greatly enhance our ability to predict the broader impacts of climate change at the coast.”
This is a drone aerial view of Narrabeen Beach in north Sydney before a storm in April 2015.
This is a drone aerial view of Narrabeen Beach in north Sydney before a storm in April 2015.
University of New South Wales
Professor Andrew Short from the University of Sydney, a co-author of the study points out that the predicted increase in intensity of El Nino and La Nina events driven by global climate change means erosion on many of Australia's beaches will be worse than previously thought.
The study, "Coastal vulnerability across the Pacific dominated by El Niño/Southern Oscillation." was published online in the journal Nature Geoscience on September 21, 2015.
More about el nino and la nina, Coastal erosion, coastal flooding, pacific basin patterns, Sea level rise