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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 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, including the University of Sydney, analysed 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. Data came from beaches in the mainland United States and Canada, Japan, Australia, New Zealand and Hawaii.

The research was published in Nature Geoscience today.

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 Ni帽o or La Ni帽a year. When the west coast of the U.S. mainland and Canada, Hawaii, and northern Japan felt the coastal impacts of El Ni帽o, 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 鈥渟uppression,鈥� such as smaller waves and less erosion. The pattern then generally flips: during La Ni帽a, the Southern Hemisphere experienced more severe conditions.

Co-author Professor Andrew Short from the School of Geosciences says forecast increases in the strength of El Ni帽o and La Ni帽a 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.

鈥淒uring enhanced La Ni帽as we can expect more tropical cyclones and east coast lows off the coast, leading to damaging cyclones and storm surges along the Queensland coast and severe beach erosion along the New South Wales coast. The more聽benign El Ni帽os will bring fewer cyclones and long periods of lower southerly waves. These will rotate the聽beaches to the聽north, building out the聽northern ends, while severely eroding the southern corners of the聽beaches, where most development usually occurs. These impacts will take place irrespective of the amount of sea level rise.

鈥淭his study significantly advances the scientific knowledge of the impacts of El Ni帽o and La Ni帽a,鈥� said Patrick Barnard, USGS coastal geologist and the lead author of the study. 鈥淯nderstanding the effects of severe storms fuelled by El Ni帽o or La Ni帽a helps coastal managers prepare communities for the expected erosion and flooding associated with this climate cycle.鈥�

The study also investigated the coastal response of other climate cycles, such as the Southern Annular Mode, which has 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 relates to atmospheric circulation in the North Pacific, are linked to coastal impacts that are more tightly restricted to the northern hemisphere.

Linking coastal erosion to natural climate patterns, such as El Ni帽o/Southern Oscillation and the Southern Annular Mode, can be challenging.

鈥淪horeline behavior can be controlled by so many different factors, both locally and regionally, that it鈥檚 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,鈥� said Patrick Barnard. 鈥淭his will greatly enhance our ability to predict the broader impacts of climate change at the coast.鈥�

鈥淐oastlines 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聽Pacific coastal communities聽prepare for the effects of changing storm regimes driven by climate oscillations like El Ni帽o and La Ni帽a. 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,鈥� said Mitchell Harley of UNSW Australia, and a coauthor of the paper.

鈥淚t's not just El Ni帽o we should be concerned about," said Ian Walker, professor of Geography at the University of Victoria and coauthor of the study. 鈥湼咔甯＠�片 shows that severe coastal erosion and flooding can occur along the British Columbia coast during both El Ni帽o and La Ni帽a storm seasons unlike further south in California. We need to prepare not only for this winter, but also what could follow when La Ni帽a comes.鈥�

The published paper, 鈥淐oastal vulnerability across the Pacific dominated by El Ni帽o/Southern Oscillation鈥� is available .听