Research Highlight: Are Pacific Waves Ready to Power Back Up?

In news that might delight surfers but make coastal homeowners anxious, a new survey of Pacific Ocean wave power suggests the intensity of breakers might ramp up as one climate regime shifts to another.

A recent study from a team at Scripps Institution of Oceanography at UC San Diego provides a new perspective on how the intensity of waves across the north Pacific Ocean has varied over the last half-century. Scripps research oceanographer Peter Bromirski used historical wind data modeled by NOAA to calculate wave power every six hours from 1948-2008, covering an expanse from California to Japan.

Two California state agencies, the California Department of Parks and Recreation Division of Boating and Waterways, and the California Energy Commission, are among the funders of the study along with NOAA. The research is part of the state’s ongoing attempt to understand future climate effects as part of an emerging strategy of mitigation and adaptation.

“The partnership between Scripps and the State of California has again produced phenomenally important information to help us all manage more wisely in the face of climate change and sea-level rise,” said Catherine Kuhlman, deputy secretary for ocean and coastal policy with the California Natural Resources Agency.

The findings are of particular importance to coastal communities and ecosystems, as extremes in wave power can cause severe flooding and beach erosion, especially in context of sea-level rise expected to take place in coming decades. California has sought to encourage consistent responses among state agencies to sea-level rise threats to water supply, coastal development, and infrastructure. One means by which the state Ocean Protection Council led by Kuhlman has done so is through the issuance of a response guide that is updated to reflect advances in research.

“We need research like this that puts wave power in historical context so that we may better anticipate coastal impacts that will be exacerbated by the rise in sea level that scientists have forecast,” said Sylvia Ortega Hunter, Deputy Director Division of Boating and Waterways, California Department of Parks and Recreation. “We must prepare for a future in which even smaller storms that currently have minimal impact have greater effects.”

Wave intensity is a result of weather patterns over ocean basins where the transfer of energy from winds to the ocean creates waves. Wave power is calculated from wave height, the distance from top to bottom of a wave, and wave period, the time between successive waves. The largest wave power measurements result when both the wave height is very large and the wave period is very long, both of which occur as a result of extreme storm events.  

The study, which was co-authored by Scripps’s Dan Cayan and John Helly, and Paul Wittmann from the U.S. Navy’s Fleet Numerical Meteorology and Oceanography Center, modeled wave power measurements in six-hour increments over a 60-year period. The model considers wind observations from a diverse set of sources over this time period, including satellite, ship, and aircraft-gathered data.

The researchers found several overall trends in how wave power changes over time in the North Pacific. None of these trends, however, can be applied to the entire North Pacific. Just as wind patterns vary widely in different parts of North America, different parts of the Pacific experience diverse regional wave power conditions.

One of the overall trends that the team identified was an increase in wave power over much of the North Pacific during winter months. In addition, wave power varies with multi-decade climate cycles known as the Pacific Decadal Oscillation (PDO) as well as the El Niño Southern Oscillation (ENSO). For example, during what oceanographers term the “warm” phase of the PDO, when sea surface temperatures along the eastern North Pacific boundary increase, wave power in much of the North Pacific also increases. Importantly, the team found that there was heightened wave power during the PDO warm phase from the mid-1970s to about 2000, with increased intensity of the most extreme wave power events. The increase in strength of the strongest events was most pronounced along parts of the U.S. West Coast.  

After about 2000, the PDO entered a “cool” phase. Along with it, there has been a general decrease in wave power in the eastern North Pacific. However, this study indicates that when the PDO does reverse to its “warm” phase, wave power may continue to increase along the West Coast. In addition, climate change is expected to increase storm intensity, which will increase wave power in the North Pacific. Taken with the results of this study, this suggests that in the future wave power levels could exceed those seen during the last warm phase.

At present, it is unclear to scientists when the PDO will shift to a warm phase.

The study, “Wave power variability and trends across the North Pacific,” appeared in the December 2013 Journal of Geophysical Research – Oceans.

–  Kelley Gallagher is a fifth-year student with microbial ecologist Paul Jensen.

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