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
UC RIVERSIDE: Slowing Atlantic current fueling stronger California storms
Study shows how ocean circulation will reshape global rainfall By Jules Bernstein, UC Riverside A slowing Atlantic Ocean current is projected to intensify powerful storms in California while reducing snowfall over Greenland, according to a new University of California, Riverside study. The Atlantic Meridional Overturning Circulation, or AMOC, works like a giant conveyor belt in the ocean, moving warm water from the tropics northward to heat places like Europe, then cycling the cooled, denser water back south along the ocean […]
NOAA RESEARCH: Groundbreaking atmospheric river forecasting collaboration crosses the finish line
From NOAA Research: A cutting-edge forecast system developed by NOAA, Colorado State University, and Scripps Institution of Oceanography at the University of California San Diego is now fully operational and providing improved precipitation forecasts of landfalling atmospheric rivers in the Bay Area. When big storms approach California, accurate and timely precipitation estimates become critical for making decisions regarding public safety, infrastructure operations, and emergency response preparations. Atmospheric rivers provide up to 50% of total annual precipitation in California but also […]
EOS: Future Hotspots of Atmospheric Rivers
Atmospheric rivers can produce heavy precipitation and associated hazards worldwide. A new study identifies regions where these hazards have already, and will further, increase with global heating. By Thomas Stacker, EOS Atmospheric rivers (ARs) are coherent current structures in the atmosphere that transport moisture and are important elements to deliver water through heavy precipitation events. They can also cause substantial hazards in many regions of the world. Due to their intrinsically long and narrow extent and high variability, it is […]
DESERT RESEARCH INSTITUTE: Accounting for soil saturation enhances atmospheric river flood warnings
Early warnings for atmospheric river-induced flooding are greatly improved by accounting for the impact of saturated soils. From the Desert Research Institute Atmospheric rivers carry unfathomable amounts of water across the sky, bringing moisture to drought-stricken regions like the Western U.S. But whether a particular incoming atmospheric river storm will result in disastrous flooding has long been difficult for researchers to determine with confidence. Now, a new DRI-led study demonstrates that accounting for soil saturation levels can substantially improve our […]
STANFORD: Physics of atmospheric rivers, explained
What drives atmospheric rivers? Da Yang explains how these “rivers in the sky” gain and lose momentum, and how researchers are studying their physical properties to improve forecasts and reduce risks. By Ula Chrobak, Stanford Doerr School of Sustainability In the winter of 1862, an estimated 37 inches of rain fell in Sacramento over two months. The newly elected governor, Leland Stanford, had to travel to his inauguration by rowboat, and the city remained flooded for months afterward. Atmospheric rivers […]
Click here for all coverage of atmospheric rivers on Maven’s Notebook.