As climate change reshapes Earth’s weather patterns, the powerful storms known as atmospheric rivers will evolve differently across the U.S. West Coast, with Southern California experiencing markedly different changes than the Pacific Northwest. New research reveals these “rivers in the sky” will bring amplified risks of coastal flooding, especially in northern regions.
Published in Nature Communications Earth & Environment | Estimated reading time: 4 minutes
Using advanced computer simulations, scientists at the National Center for Atmospheric Research (NCAR) have uncovered how these moisture-laden atmospheric phenomena will respond to warming conditions. Their findings suggest that by 2100, atmospheric rivers striking the Pacific Northwest could triple their impact on coastal water levels compared to current storms, assuming continued high greenhouse gas emissions.
“On the ground, people will see a different response between the Southern California coast and the Pacific Northwest,” said Dr. Christine Shields, NCAR scientist and co-lead author of the study. “It’s not a one-size-fits-all situation. You have these regional responses that can be quite different.”
The research team employed a high-resolution computer model capable of simulating atmospheric processes every 25 kilometers and ocean processes every 10 kilometers—fine enough to recreate individual ocean eddies. This unprecedented detail required the use of the Derecho supercomputer at the NCAR-Wyoming Supercomputing Center.
A Tale of Two Regions
In Southern California, atmospheric rivers known as “Pineapple Express” events will be primarily affected by increased evaporation of ocean waters. This process temporarily cools the atmosphere and drives the storms forward with greater intensity. However, atmospheric rivers striking Northern California and the Pacific Northwest will be more influenced by overall warming in both the atmosphere and ocean, leading to more powerful storms and dramatic temporary increases in sea level as they approach the coast.
The study found that these regional differences stem from the distinct characteristics of atmospheric rivers in each area. The Pineapple Express follows a subtropical jet of very moist air from Hawaii to Southern California, while northern atmospheric rivers are typically associated with a less moist polar jet of air, resulting in windier and more meandering storms.
“Atmospheric rivers are like tropical cyclones in that they pack powerful winds and carry enormous amounts of water that can devastate local infrastructure,” Shields explained. “Communities need to understand how they will change in the future so they can adapt and plan.”
Glossary
- Atmospheric River
- A long, narrow corridor of concentrated moisture in the atmosphere that can transport vast amounts of water vapor from tropical regions to higher latitudes.
- Pineapple Express
- A specific type of atmospheric river that transports moisture from near Hawaii to the U.S. West Coast along a subtropical jet stream.
- Sea Surface Height
- The height of the ocean’s surface relative to a reference point, which can be temporarily elevated by strong winds pushing water toward the coast.
Test Your Knowledge
What is the primary factor affecting atmospheric rivers in Southern California under climate change?
Increased evaporation of ocean waters is the main factor influencing atmospheric rivers in Southern California, temporarily cooling the atmosphere and propelling the storms forward.
By approximately how much could atmospheric rivers increase coastal water levels in the Pacific Northwest by 2100?
The study found that atmospheric rivers could triple their impact on coastal water levels in the Pacific Northwest compared to current storms.
How do atmospheric rivers in Northern California differ from those in Southern California?
Northern California atmospheric rivers are typically associated with a less moist polar jet of air and tend to be windier and more meandering, while Southern California’s “Pineapple Express” events follow a subtropical jet of very moist air from Hawaii.
What makes this study’s computer modeling approach unique?
The study used high-resolution simulations capable of modeling atmospheric processes every 25 kilometers and ocean processes every 10 kilometers, allowing them to recreate individual ocean eddies with unprecedented detail.
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