California is known for its sunny beaches and surfing culture, but it is also home to some of the most powerful and dangerous waves in the world.
These waves are especially strong and frequent during the winter season when storms over the North Pacific Ocean generate large swells that travel thousands of kilometers to reach the California coast.
These winter waves can pose a threat to coastal communities and infrastructure, as well as to marine life and ecosystems.
But how have these winter waves changed over time, and what are the factors that influence their variability and trends?
A new study by a researcher from UC San Diego Scripps Institution of Oceanography has shed some light on these questions, using a novel method to reconstruct the history of winter wave heights in California over the past 90 years.
How to measure winter wave heights using seismic data
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The study, published in the Journal of Geophysical Research-Oceans, was conducted by Peter Bromirski, a researcher emeritus at Scripps, as per Phys.org.
Bromirski used a unique but accepted method to estimate winter wave heights using seismic data, which are records of vibrations in the Earth's crust caused by earthquakes or other sources.
He first developed this method in 19992, when he realized that seismic data could also capture the signals of ocean waves hitting the shore.
The researcher explained that when ocean waves reach shallow coastal waters, some of their energy is reflected back to sea, where it collides with incoming waves.
This interaction creates downward pressure on the seafloor, which generates seismic waves that propagate inland and can be detected by seismometers.
The strength of these seismic waves is directly proportional to the height of the ocean waves, which allows Bromirski to calculate one from the other.
Bromirski used this method to analyze seismic data from UC Berkeley, which has been collecting records since 1931.
He focused on the winter months of December, January, and February when the wave activity is highest in California.
He also filtered out the noise from earthquakes and other sources, which he said was easier than it sounds because they have different durations and frequencies than ocean waves.
What are the results and implications of the study?
The results of the study showed that winter wave heights in California have increased significantly since 1970, coinciding with the acceleration of global warming, as per Newsweek.
Bromirski found that the average winter wave height has increased by 13% or about 0.3 meters (one foot) compared to the period before 1970.
He also found that there were more frequent and intense events of large waves (>4 meters or 13 feet) after 1970 than before.
The implications of the study are important for understanding and predicting the impacts of climate change on California's coast.
Bromirski suggested that the increase in winter wave heights was related to the increase in storm activity over the North Pacific Ocean, which is driven by changes in atmospheric pressure and wind patterns associated with climate change.
He also warned that higher winter waves could exacerbate coastal flooding and erosion, especially in combination with sea level rise and El Niño events.
The study also highlighted the need for more research and monitoring of winter wave heights in California, as well as other regions around the world.
Bromirski said that his method could be applied to other locations where long-term seismic data are available, such as Japan or Hawaii.
He also said that his method could be complemented by other sources of data, such as satellite imagery or buoy measurements, to improve the accuracy and resolution of wave height estimates.
