Photo: Paul Chinn, The Chronicle This year’s El Niño may be stronger that the version that hit California in 1997-1998 rainy season. Here are photos from the 1997-1998 El Niño: A storm-damaged section of the Great Highway south of Sloat Boulevard in March 2012.
By David Perlman SF CHRON Updated 7:04 pm, Monday, September 21, 2015
The seacoasts of California and nations on both sides of the Pacific are likely to be battered in coming years by increasingly high waves pushed ashore by ever-stronger weather patterns, leaving them vulnerable to destructive erosion, an international group of experts said Monday. Those intensified weather patterns such as El Niño, when warmer eastern Pacific waters contribute to more intense storms hitting California, will increasingly threaten the coasts irrespective of climate change, said an international team of 17 coastal experts. Severe weather events across the entire Pacific basin have been increasing for more than 30 years and are expected to double in frequency in coming years, the scientists said in a report published in the journal Nature Geoscience. Only five years ago, an unusual weather pattern during an El Niño winter brought extreme wave heights and unprecedented erosion that tore away protective revetments along more than 3 miles of San Francisco’s Ocean Beach and damaged the Great Highway. Patrick Barnard, the leading coastal geologist at the U.S. Geological Survey’s Marine Science Center in Santa Cruz and principal author of the new study, said Ocean Beach has since recovered, and other beaches in the Bay Area “now look in moderately decent shape.” But in the long term, Barnard said, such areas are going to become increasingly vulnerable to erosion brought about by surging storms. And it isn’t only El Niño events that are the problem: Intensified episodes of El Niño’s meteorological opposite, called La Niña, when the eastern and central Pacific becomes abnormally cold, are likely to threaten coastal regions in New Zealand, Australia and elsewhere in the Southern Hemisphere, the report said. The coastal scientists who compiled the new report surveyed 48 beaches bordering the Pacific and analyzed detailed climate events around the Pacific stretching from 1979 to 2012 to reach their forecasts. They also considered forecasts of extreme La Niña and El Niño events published recently by a separate group of international climate and coastal scientists led by Wenju Cai, a climate modeler at Australia’s Scientific and Industrial Research Organization, Barnard said. The Cai group predicted that increased global warming and rising sea levels due to climate change would double the frequency of those severe weather events across the Pacific basin. The result, the group said in a report published this year in the journal Nature Climate Change, would be “more occurrences of devastating weather events and more frequent swings of opposite extremes from one year to the next, with profound socio-economic consequences.”
Barnard et al. Nature Geoscience (2015) doi:10.1038/ngeo2539 Received 29 June 2015 Accepted 17 August 2015 Published online 21 September 2015
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.