An atmospheric river is a long, narrow corridor of concentrated moisture in the atmosphere that can transport vast amounts of water vapor from the tropics to other regions – on average, an atmospheric river can transport as much water as 20 Mississippi Rivers.
Atmospheric rivers are a key feature in the California water cycle. Half of California’s water supply comes from atmospheric rivers, often in powerful downpours that can hit in rapid succession. On the flip side, fewer atmospheric rivers generally leads to California progressing into drought. California often doesn’t get out of a drought until an atmospheric river arrives; seven of the last 12 droughts ended with atmospheric rivers.
On average, California usually sees about five or six atmospheric rivers, but some years it can be as few as one or two. Researchers are continuing to study why some years have so many, and others, so few.
Similar to hurricanes or tornadoes, a rating scale for atmospheric rivers has been developed that ranks atmospheric rivers by its physical characteristics, such as water vapor or wind speed, and the level of potential destruction it might cause. However, unlike other rating systems, the atmospheric river system incorporates the idea that atmospheric rivers can be beneficial, hazardous, or both. On the low end of the scale, AR Cat 1 events rated as primarily beneficial and at the high end, AR Cat 5 events primarily hazardous.
Climate change is amplifying the severity of many extreme weather events, including atmospheric rivers, particularly in California. Research by USGS scientists and their collaborators has revealed that, over the past 70 years, there has been a trend of increasing water vapor transport to the West Coast linked to warming ocean surfaces. While atmospheric rivers are not expected to become more frequent, California’s precipitation patterns are projected to become more erratic, with a greater amount of water concentrated in fewer, more intense atmospheric river events.
WEB RESOURCES
- Center for Western Weather & Water Extremes: CW3E provides weather predictions, climate projections, atmospheric river forecasts, interactive maps, research and publications, and workshops and collaborations.
- NOAA Atmospheric River Portal: Access information, images, analyses, diagnostics of current conditions, forecasts, and projects related to atmospheric rivers (ARs).
Story map from the Center for Western Weather & Water Extremes
Coverage of atmospheric rivers on Maven’s Notebook
NOTEBOOK FEATURE: Atmospheric rivers from research to reconnaissance: A conversation with research meteorologist Marty Ralph
By Robin Meadows In the late 1990s, hardly anyone had heard of the storms called atmospheric rivers. That includes Marty Ralph, founding director of Center for Western Weather and Water Extremes (CW3E) and a leading expert on these relatively recently recognized streams of water vapor in the sky. Atmospheric rivers are long, narrow plumes of exceptionally wet air that shoot across the ocean and drop rain or snow when they hit land. These storms deliver much of the precipitation and […]
NOTEBOOK FEATURE: How the fight against Auburn Dam advanced flood control in California
by Robin Meadows In 1990, Gary Estes moved to Auburn, a town of nearly 14,000 in the Sierra Nevada foothills on the North Fork of the American River. Estes, an environmentalist, immediately joined the fight against Auburn Dam. The proposed dam site was only about one mile from his house. The U.S. Army Corps of Engineers wanted to build Auburn Dam to boost flood control in the city of Sacramento, which is about 30 miles downstream of Auburn and which […]
DR. MICHAEL ANDERSON: Climate change and California’s water resources
California’s climate is changing, with atmospheric rivers and extreme events occurring more frequently. This is not the new normal; we’re just getting started, says state climatologist Dr. Michael Anderson in this presentation at the California Irrigation Institute’s 2024 annual meeting. In this presentation, Dr. Anderson talked about how climate change is altering water availability, the rise in extreme events, the increasing variability of the climate, and the importance of flexible water management strategies. How a snowpack does (or does not) […]
BERKELEY LAB: Unraveling the Mysteries of Consecutive Atmospheric River Events
Berkeley Lab scientists are investigating the characteristics and impacts of back-to-back atmospheric river events By Julie Bobyock, Berkeley Lab In California’s 2022-2023 winter season, the state faced nine atmospheric rivers (ARs) that led to extreme flooding, landslides, and power outages – the longest duration of continuous AR conditions in the past 70 years. Scientists at Lawrence Berkeley National Laboratory (Berkeley Lab) recently conducted a study using machine learning to better understand these complex weather systems, finding that more intense atmospheric […]
EOS: California mountains face weather whiplash
Last month’s massive snowstorm in the Sierra Nevada followed a dry start to winter. Such extremes in precipitation may become the norm. By Andrew Chapman, EOS In late February 2024, residents of California and Nevada communities surrounding Lake Tahoe were starting to wonder whether winter would ever come. Warm temperatures and rain had left shovels and snowblowers untouched, local skiers discouraged, and water and disaster managers wondering what the year’s water supply and fire hazard would look like. “Our snowpack […]
Click here for all coverage of atmospheric rivers on Maven’s Notebook.