A new study has found that powerful atmospheric rivers—narrow bands of concentrated moisture that deliver heavy rain and strong winds—could significantly contribute to sea level rise along the West Coast, exacerbating the risks of coastal flooding in the coming decades.
Researchers conducted simulations to assess how atmospheric rivers (ARs) influence ocean processes, focusing on their effects on sea surface height.
The study's findings, published in Communications Earth & Environment, indicate that during these AR events, strong winds push ocean water toward the coast, piling up against land barriers and raising sea levels dramatically.
In regions such as Southern California and the Pacific Northwest, sea level increases caused by ARs could exceed 200 percent under worst-case scenarios of future global warming.
"To date, much of the climate change impacts literature is focused over land and population centers due to the potential for ARs to cause major flooding or relieve drought, so here we wanted to focus on the impact ARs have on the ocean," Christine Shields, the lead author of the study, told Newsweek.
"We find that ARs do have a big impact on things like sea surface height, ultimately pushing water toward the coast. Under climate change, this will amplify," she continued.
ARs are notorious for their role in delivering massive amounts of precipitation. The National Oceanic and Atmospheric Administration describes them as "rivers in the sky." Similar to terrestrial rivers, these bands of moisture flow, moving through the atmosphere where they're propelled by strong winds.
ARs are well known for delivering vast amounts of precipitation, often resulting in flooding and mudslides. They transport concentrated moisture through the atmosphere, much like rivers on land.
Driven by powerful winds, these moisture-laden bands flow across the sky, capable of releasing heavy rainfall when they reach land.
While ARs are typically associated with rain-induced damage, the research highlights another important effect: their ability to influence ocean dynamics. The powerful winds and turbulence they generate not only stir the upper ocean layers but also contribute to rising sea levels through increased wind stress.
"Atmospheric rivers push the water along with the flow at the surface," Shields said. "The winds from the air interact with the ocean surface, and when an AR approaches the coast, the ocean surface currents change to cause the sea surface height to increase along the coast."
The simulations used by the researchers provided a more detailed picture of how atmospheric rivers interact with the ocean than was previously available, showing that wind stress during AR events can lead to substantial increases in sea surface height along the coast.
"The overall strong and prevailing westerly AR winds push the warmer water towards the coast, resulting in a significant and robust increase in sea surface height along the North American west coastline. In fact, under the projected warming, the coastal sea level rise caused by Southern California and Pacific Northwest ARs can exceed 200 percent," the authors wrote in the paper.
Shields added: "The implications are that in a warmer world, ARs could contribute to local and temporary flooding along the coast to a much higher degree than what occurs now. City and state resource managers, operations, etc., need to plan so that communities can handle the potential influx of sea water during ARs."
The study highlights that while the general mechanism of AR-induced sea level rise applies across the West Coast, the effects are not uniform. Southern California could see the highest increases in sea level due to the predominance of "Pineapple Express" ARs, which carry moisture from the tropics. These ARs tend to be warmer and wetter, leading to more pronounced effects on sea surface height.
In contrast, regions such as Northern California and the Pacific Northwest, where ARs frequently overlap with extratropical storm systems, may experience more diffuse but still significant effects.
The research also explored the future under projected warming scenarios, showing that the intensity of ARs—and their effects on sea level rise—would likely increase.
Using the Representative Concentration Pathway 8.5 model, a worst-case emissions scenario, the study found that future AR events would bring more intense wind-driven sea level surges.
The authors wrote, "Although consensus on AR climate change signals for metrics such as frequency, duration, and location of landfall along North American coastlines is still uncertain, stakeholders in coastal communities still need to plan for all possible scenarios."
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Reference
Shields, C. A., Li, H., Castruccio, F. S., Fu, D., Nardi, K., Liu, X., & Zarzycki, C. (2024). Response of the upper ocean to northeast Pacific atmospheric rivers under climate change. Communications Earth & Environment, 5(1), 1–12. https://doi.org/10.1038/s43247-024-01774-0
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