what’s new

Atmospheric rivers — narrow bands of concentrated water vapor transported poleward from the tropics — don’t just bring a deluge of precipitation, they play a key role in extreme heat and warming winters across the United States, new research suggests.

This winter has already kicked off with atmospheric rivers on both the East and West coasts, causing widespread flooding but also easing drought in some regions.

However, the new study also suggests that these weather systems bring heat into the lower atmosphere, creating temperature anomalies of 9-18 F above average.

These impacts are particularly pronounced in regions such as the Pacific Northwest, Midwest, and Eastern US, where atmospheric rivers are associated with warm winters and extreme heat waves.

Why it matters

The findings underscore an overlooked consequence of atmospheric rivers in the U.S. and more generally around the world: their ability to amplify extreme temperatures, exacerbate heat waves, and create unusually warm winters.

As atmospheric rivers are expected to become more intense and frequent as a result of climate change, their impact on temperature extremes could pose new challenges for infrastructure, agriculture and public health.

Improved forecasting of heat events caused by AR could help communities prepare for these risks.

What to know

The study found several significant regional impacts for the US

In the Pacific Northwest, an atmospheric river contributed to record heat waves in 2021, intensifying heat in the region. The researchers found a significant correlation between the frequency of atmospheric rivers and seasonal average temperatures.

The impacts may not be limited to places where the atmospheric river hits land either. The 2021 heat wave showed lingering effects far from where it hit southeast Alaska.

Atmospheric rivers penetrate further inland in the Midwest, probably due to the absence of mountain barriers. Here, they can warm the area by about 1 F on average in the winter.

The North Atlantic, North Pacific, and Southern Ocean are hotspots for AR-driven warming. ARs in winter contribute to significant warming in northern Europe and eastern North America.

Overall, more than 70 percent of the hourly extreme temperature anomalies in the midlatitudes occur during the AR. In polar regions, extreme heat events are up to 10 times more likely to coincide with AR than if the events were independent.

What people are saying

“Once we identify AR spatial footprints, we can look at how conditions inside the feature differ from the outside environment. This allows us to see changes in temperature, heat transfer, and other important variables that occur during these events.”

She also pointed out that the work is important for highlighting other, lesser-known impacts of atmospheric rivers.

“Although we usually hear about atmospheric rivers in the context of the West Coast, the effects on temperatures occur across the country, especially in the central and eastern regions,” Scholz said.

“For example, the connection between atmospheric rivers and extreme temperature anomalies is strongest east of the Mississippi and in the winter season.”

What will happen next?

As atmospheric rivers intensify and become more frequent due to climate change, researchers are increasingly focusing on their role in exacerbating heat waves, as evidenced by the 2021 event in the Pacific Northwest.

The scientists stressed the importance of further investigating the connection between heat waves and atmospheric rivers. In particular, humid heat waves pose a significant threat to public health because high humidity makes it difficult to maintain body temperature and keep cool.

Link

Scholz, SR, Lora, JM (2024). Atmospheric rivers cause warm winters and extreme heat. Nature. https://doi.org/10.1038/s41586-024-08238-7

Update 12/18/24 11:24 AM ET: The article has been updated with comments from Serena Scholz.