Atmospheric Rivers Set To Increase in US

Atmospheric rivers are set to increase around in the U.S. and around the globe if climate change continues to worsen, a study has found.

Atmospheric rivers are corridors of concentrated, tropical moisture that travel through the atmosphere. They transport this moisture from the equator towards the North and South Poles. And when they arrive, they cause a deluge of rainfall. In fact, they are responsible for about 20 to 30 percent of all rain and snowfall across the western U.S.

California has seen extreme rainfall from two atmospheric rivers this month, causing some severe flooding in some areas. A series of atmospheric rivers also caused rain and flooding last year. The amount of rainfall this caused was historic for the area.

Climate change is only going to make them worse, a study has found.

The research, published in Journal of Geophysical Research: Atmospheres, used climate models to analyze how atmospheric rivers are changing, and will continue to change between 1980 and 2099, as the globe continues to warm.

"Our projections, utilizing advanced data, suggest a marked increase in the frequency of atmospheric rivers along both the western and eastern coastlines of the USA," study author Mengqian Lu, associate professor at the department of civil and environmental engineering at the Hong Kong University of Science and Technology, told Newsweek.

"Additionally, these atmospheric rivers are expected to migrate towards higher latitudes, significantly heightening the risk of severe weather events in Alaska. A closer examination of their landfall characteristics, particularly along the western coast—commonly impacted by 'Pineapple Express' systems—reveals that not only will atmospheric rivers make landfall more frequently, but they are also likely to persist longer and maintain their strength as strong atmospheric rivers. Consequently, we can anticipate a surge in atmospheric river-driven precipitation, elevating the potential for extreme weather conditions and increased flooding risks."

They found that moisture content in the air will only increase due to rising surface temperatures. This will increase the number of atmospheric rivers that form, and the extreme weather that they often bring.

In a scenario of intense fossil fuel use in which greenhouse gases are pumped into the atmosphere at the same rate, the researchers estimate that atmospheric rivers will increase by 84 percent in the months between December and February, and 113 percent between June and August.

Even in a medium scenario for greenhouse gas emissions, they will still increase by 34 to 46 percent, the study reported.

Many areas of the globe will be affected by moisture will increase the most over the north Indian Ocean. In this area, researchers estimate that atmospheric rivers could triple in frequency as climate change worsens.

Another notable area will be Greenland, which could see less of an interval between atmospheric rivers, depending on fossil fuel use.

Overall, areas where there is already a high amount of precipitation could see severe and disruptive changes. This extreme weather could mean damage to infrastructure and dangerous flooding.

"Polar regions, like Greenland, and tropical regions, like Northern India, also face considerably heightened risks associated with [atmospheric rivers] which warrant serious attention and should not be underestimated," the authors wrote in the study.

An increase in extreme weather events is already being seen across the world. These are not just occurring in the form of intense storms, but also extreme heat, drought and wildfires.

The western U.S. for example, has seen both sides of this coin in recent years. Before experiencing an increase in heavy rain, the southwest was in the grips of an ongoing megadrought, suffering with extremely dry conditions.

But the region is seeing a "whiplash effect" where these extremely dry conditions were then followed with periods of extreme storms and rain.

Lu and colleagues will continue to look into this topic to find out more.

"We are anticipating the publication of two more papers in the near future. The first is set to be featured in the prestigious npj Climate and Atmospheric Science, a journal within the high-impact Nature portfolio," Lu said.

"This paper conducts an in-depth analysis of cross-Pacific atmospheric rivers that have significant effects on the western coast of the United States. The second paper delves into the initiating mechanisms of atmospheric rivers to be published in another high-impact journal Geophysical Research Letters, with the aim of improving atmospheric river predictability. Our research in this area has the potential to greatly enhance forecasting models for these impactful weather events."

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