Atmospheric River Storms: What They Are and How They Affect California

Atmospheric River Storms: What They Are and How They Affect California
Atmospheric River Storms: What They Are and How They Affect California

What is an atmospheric river?

An atmospheric river is a long, narrow band of moist air that transports water vapor from the tropics to higher latitudes. They are often associated with strong winds and low pressure systems, and can stretch for thousands of miles across the ocean. Atmospheric rivers can deliver large amounts of rain or snow to the regions they hit, especially along the coast and in the mountains. They are responsible for about 30% to 50% of the annual precipitation in the western United States¹.

Why are atmospheric rivers important for California?

California depends on atmospheric rivers for much of its water supply, especially during the winter months. The snowpack in the Sierra Nevada mountains, which provides about a third of the state’s water, is largely influenced by atmospheric rivers². Atmospheric rivers also help replenish the groundwater and reservoirs that are vital for agriculture, industry, and urban use.

However, atmospheric rivers can also pose significant hazards for California, such as flooding, landslides, mudslides, and erosion. Some of the most damaging storms in the state’s history have been linked to atmospheric rivers, such as the 1861-1862 flood that turned the Central Valley into a lake, the 1986 flood that caused $400 million in damages, and the 1997 flood that affected 48 counties and killed 17 people³.

How are atmospheric rivers changing due to climate change?

Climate change is expected to affect the frequency, intensity, and duration of atmospheric rivers in the future. According to a recent study, the number of atmospheric rivers hitting California could increase by about 35% by the end of the century under a high-emissions scenario⁴. The study also found that the strongest atmospheric rivers could become more extreme, delivering up to 25% more water than they do now. This could lead to more severe floods and droughts, as well as challenges for water management and infrastructure.

How can we prepare for and adapt to atmospheric rivers?

To cope with the impacts of atmospheric rivers, California needs to improve its monitoring, forecasting, and warning systems, as well as its emergency response and recovery plans. The state also needs to invest in more resilient and flexible water infrastructure, such as dams, levees, aqueducts, and desalination plants. Moreover, the state needs to promote water conservation and efficiency, as well as the use of alternative water sources, such as recycled water and stormwater capture. Finally, the state needs to reduce its greenhouse gas emissions and support global efforts to mitigate climate change, which is the main driver of atmospheric river changes.


Atmospheric rivers are a vital but also a volatile source of water for California. They bring both benefits and risks for the state, and these are likely to increase in the future due to climate change. Therefore, California needs to be aware of and prepared for the challenges and opportunities that atmospheric rivers present, and to take actions to enhance its water security and resilience.

California Braces for Back-To-Back Atmospheric River Storms.

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