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Our changing climate is set to dramatically alter the atmospheric rivers—powerful storms that carry huge amounts of water vapor and heavy rainfall—that scour the West Coast of the United States.

This follows from a new study by the US National Science Foundation’s National Center for Atmospheric Research (NSF NCAR), published in the journal Nature Communication Earth and Environment.

As the planet warms, storms will develop differently in Southern California and the Pacific Northwest—regions regularly hit by atmospheric rivers, especially in the winter months.

Southern California will experience intensified storms due to increased ocean evaporation, while atmospheric rivers in the Pacific Northwest will be stronger, driven by rising ocean and atmospheric temperatures.

Why it matters

Atmospheric rivers are often described as “rivers in the sky”, delivering essential precipitation and replenishing snowpacks in an area that depends on them for water supply.

According to the National Oceanic and Atmospheric Administration (NOAA), they can carry water at up to 15 times the flow rates of the Mississippi River estuary.

Just in the past few weeks, the region has been battered by such storms, with more on the way as we head into the holiday season.

However, their increasing intensity poses a significant threat to coastal communities.

By 2100, storms in the Pacific Northwest could temporarily raise ocean levels up to three times their current level, dramatically increasing the risk of flooding, the study warns.

Residents of Southern California will also face rising waters, albeit to a lesser extent.

“Communities need to understand how they will change in the future in order to adapt and plan,” Christine Shields, an NSF NCAR research scientist and co-author of the study, said in a statement.

What to know

Using advanced climate simulations, the research team explored how future atmospheric rivers will interact with ocean conditions such as surface temperatures and water mixing.

Their high-resolution modeling, run on the NSF NCAR-Wyoming Supercomputing Center’s Derecho supercomputer, provided unprecedented detail and revealed stark regional differences in how these storms will behave.

The modeling was so granular that scientists were able to examine atmospheric river processes in 16-mile steps and ocean processes in 6-mile steps. For context, atmospheric rivers often stretch thousands of miles across the ocean.

Atmospheric rivers are typically driven forward by the evaporation of ocean waters, which temporarily cool the atmosphere providing the storm’s propulsion.

In Southern California, warming oceans will intensify the effects of the “Pineapple Express,” a type of atmospheric river that brings moisture from Hawaii.

Meanwhile, storms hitting the Pacific Northwest will begin to be fueled by a combination of atmospheric and oceanic warming, resulting in increased precipitation, stronger winds, and sea level rise during landfall.

Atmospheric rivers in the Pacific Northwest already tend to be windier and more meandering than their southern counterparts.

“Strong winds and precipitation associated with atmospheric rivers can significantly affect the upper ocean and potentially affect ocean dynamics and ecosystems at larger spatial scales and longer timescales than at present,” Hui Li, another co-author, said in a statement.

What they say

Christine Shields, NSF NCAR research scientist and co-author of the study: “On the ground, people will see a different response between the Southern California coast and the Pacific Northwest. It’s not a universal situation. You have these regional responses that can be quite different.”

Hui Li, another co-author: “It is important to understand the influence of atmospheric rivers under the current climate and how they may change in the future.”

What will happen next?

The findings highlight the critical need for tailored strategies to address regional challenges.

More research is needed to determine the exact reasons for these different effects, but regardless, the impact will be felt by the millions of people who call the West Coast home, especially if greenhouse gas emissions are not adequately curbed in the coming years.

Link

Shields, C. A., Li, H., Castruccio, F. S., Fu, D., Nardi, K., Liu, X., & Zarzycki, C. (2024). Upper ocean response to atmospheric rivers in the northeast Pacific under climate change. Earth and environment communication, 5(1), 1–12. https://doi.org/10.1038/s43247-024-01774-0