Will Atmospheric Rivers Sink California’s Shores?

Future Atmospheric Rivers May Pose a Rising Threat to Coastal Communities Along the US West Coast

I grew up in a coastal town in the western Mediterranean. It is one of these towns where families have lived for generations: great-grandmas, grandmas, mothers, and children from these families have grown and lived together for centuries.

All my family still lives there, and they take great pride in the family history, just like the rest of the town. So much so that every decade, they publish a new book with collections of photos dating from the early 1900s to the present, and they sometimes make photo exhibits where they all locate their ancestors in worn-down black-and-white photographs. It’s quite an experience.

It was during one of these sessions that I spotted something interesting: a concrete restaurant on the town’s beach in the shape of a ship. They called it “El Barco,” The Ship.

My dad explained that it used to be a very popular spot for everyone to hang out. Unfortunately, it was lost to the sea during one of these Mediterranean spring storms. After that, they learned the lesson, and new laws were passed to prevent people from building this close to the shore.

This got me thinking. Here in the US, we are experiencing the severe effects of climate change on the coasts. Are we ready for them? Can we pass new legislation to protect us from significant damage? More importantly, how severe can future events become?

Well, today’s story has something to say about it!

Climate change impacts are often associated with rising temperatures and extreme weather events. We know that, right? However, a new study is highlighting an unexpected consequence of global warming: intensified atmospheric rivers (ARs) that could drive significant ocean level rises along the West Coast of North America.

But first, what are ARs? ARs are long, narrow bands of concentrated water vapor that flow through the sky, usually moving from tropical to higher latitudes. They act as natural “conveyor belts” for moisture, carrying massive amounts of water vapor — up to 15 times the flow of the Mississippi River — over long distances.

When ARs make landfall, they release this moisture as heavy rain or snow, which can lead to significant precipitation, often beneficial during droughts but potentially causing floods when intense. See the NOAA infographic below.

I guess that the definition sounds familiar if you’ve been following the news.

But let’s go back to today’s research, shall we?

The research explores how future ARs might become even more powerful, raising sea levels in ways that resemble storm surges from hurricanes. This potential impact could mean more frequent and severe flooding for coastal communities, particularly in California, stressing the need for preparedness and adaptation strategies.

Atmospheric rivers are not a new phenomenon, but their influence on ocean levels has received limited attention. Until now. These ARs, which account for around 90% of the Earth’s water vapor movement between the equator and the poles, are infamous for their role in heavy precipitation events, sometimes as “drought-busters” in dry regions but often as catalysts for severe floods.

The team behind this new study focused on understanding how rising global temperatures might alter ARs and amplify their impacts on the oceans. One report on the study emphasized that the researchers set out to find “what sort of ocean level rise North America might expect” as climate change drives more intense ARs to the shores of California, Oregon, and Washington.

The researchers from the National Center for Atmospheric Research, Texas A&M University, and Pennsylvania State University relied on a sophisticated high-resolution Earth System Model to investigate. This model allowed them to examine previous AR events, incorporate data from recent storms, and simulate how these phenomena might behave under different climate change scenarios, what we call climate modeling.

For their work, they adjusted factors such as predicted air and ocean temperatures to see how future ARs might impact the coastal areas where they make landfall. This modeling approach is particularly powerful because it accounts for both ocean and atmospheric conditions, capturing the complex ways in which ARs affect upper ocean dynamics.

Using this method, they could provide a realistic view of what future AR-driven ocean level rises might look like along the West Coast. I know it sounds like magic, but it’s ‘just’ science!

So, what did they find?

The results point to a significant increase in coastal ocean levels during AR events — up to 200% compared to those observed in the past, which could be catastrophic for communities along California’s coast. The thing is that, unlike typical tides or storm surges, this ocean level rise is primarily driven by the strong winds associated with ARs, which push seawater toward the coast and elevate sea surface heights (SSH) near land.

This effect could spell trouble for Southern California in particular, where more intense ARs are expected to hit, bringing with them increased rainfall and wind speeds. This region, prone to the so-called “Pineapple Express” storms that transport moisture from the tropical Pacific to the California coast, might face amplified impacts due to the frequency and strength of future AR events.

However, the study’s authors noted that the risk of flooding isn’t uniform along the coast, with Southern California likely bearing the brunt of this projected ocean level rise. The simulations suggest that Los Angeles and surrounding areas will face higher ocean levels than northern California due to differences in storm structure and the region’s geography.

As another article covering the study reported, “parts in the south…are likely to see more ARs, each bringing more rain and wind than has been seen in the past,” meaning these coastal areas could experience particularly heightened ocean levels.

Meanwhile, regions farther north, though still affected, may not see quite the same increase in flood risk, though AR events there are also expected to grow in intensity. That doesn’t sound good, does it?

As you can imagine, these findings add urgency to the ongoing conversation around climate resilience for West Coast communities. AR-driven ocean level rise can produce flooding similar to storm surges, posing direct threats to coastal infrastructure, homes, and ecosystems.

The researchers point out that, like with hurricanes, there’s a real need for coastal areas to plan for these changes and anticipate what heightened AR activity could mean for long-term safety. For coastal planners, policymakers, and residents alike, the take-home message is clear: ARs could have a greater impact on the West Coast than previously thought, especially in the context of rising global temperatures. And we need to be prepared for that.

This research highlights the importance of preparing for more intense ARs and their impacts on ocean levels. While atmospheric rivers might not be as high-profile as hurricanes, they could soon become a central factor in discussions about West Coast climate risks.

Planning for a future with intensified ARs means building resilience into coastal infrastructure, re-evaluating flood defenses, and, above all, being ready for the changes that warmer temperatures are likely to bring to our oceans and shores.

For the communities and coastlines of the West Coast, the next century of AR activity could prove to be a defining challenge. And we must prepare and adapt for what’s coming.