What Do Atmospheric Rivers Portend?
Californians are rightfully concerned about drought and wildfire. Tuolumne County’s elevation somewhat mitigates these challenges, as storms rise over our mountains and produce rain and snow. But now rainstorms are recognized as another cause for worry. About 30 percent of our average annual rainfall comes to California from atmospheric rivers – bands of water vapor transferring tropical moisture to other latitudes – which have ended 33 – 74 percent of droughts in the West from 1950 to 2010 (1).
Atmospheric rivers can be 250 to 375 miles wide and 1,000 miles long, carrying the equivalent of twice the capacity of the Amazon River (3). Recent record atmospheric rivers have been much larger. If a storm stalls over a land mass, the impacts (floods, mudslides, etc.) can be catastrophic.
Warmer waters mean bigger storms. Moisture available to developing storms increases about 4 percent per degree of warming of the Pacific Ocean. This isn’t the average warming of the ocean; rather, it is the temperature of tropical waters surrounding a forming storm. The water temperature causes the surrounding air to warm and expand thereby holding more moisture. The storm becomes wetter and more powerful.
The average surface temperature of our oceans is about 68°F. But local temperatures can vary—during the last couple of years, record ocean temperatures off Florida’s coast have reached 101°F (2).
About 91 percent of the excess heat produced by global warming is absorbed by Earth’s oceans. Since 2000, the pace of global warming has doubled, fueling predictions that total precipitation caused by atmospheric rivers could increase by 40 percent. Additionally, atmospheric rivers could become 25 percent wider and longer and occur more rapidly (1).
Humanity has built towns and cities near watersheds because humans need water to drink, grow crops, and support industry. Watersheds must be rethought, since sudden storms that drop record amounts of rain can easily flood ordinarily safe areas (1). We need to be aware of and meet the demands of more powerful storms (3). To begin with, we must support climate science to understand these threats better and develop appropriate warning systems (2).
As with wildfires and heat domes, atmospheric rivers are intensifying, and costly catastrophic damage demonstrates beyond the established science that global warming is happening and must be curtailed. The well-being of future generations depends on our actions today.
Take Action
- Vote in local and national elections for candidates who address global warming.
- Participate in community energy-efficiency programs and local planning meetings.
- Support recycling and waste reduction. Attend the Solid Waste Committee which meets as needed on the Second Wednesday of each month at 1:00 p.m. in the A.N.F. Building – Conference Room 3-A, located on the 3rd Floor of 48 Yaney Ave, Sonora.
- Reduce driving and flying, use less electricity, eat less beef and dairy, buy fewer goods and services–just a simpler life.
NOTES
- Tess Turner, “How Big a Climate Threat Are Atmospheric Rivers,” Council on Foreign Relations, March 22, 2024.
- Ula Chrobak, “Physics of Atmospheric Rivers, Explained,” Stanford Doerr School of Sustainability, Stanford University, December 18, 2025.
- F. Martin Ralph, Michael Dettinger, Paul Neiman, “Atmospheric Rivers in the Northwest,” Climate Hubs, U.S. Department of Agriculture, December 2025.