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
USGS: Causes and consequences of flooding in California’s Central Valley
From USGS Ecosystems Land Change Science Program: USGS researchers are leveraging advances in satellite-based monitoring to better characterize and predict flood inundation, which is essential for effective emergency response and water management planning. Atmospheric rivers (ARs) are long corridors of water vapor transport that extend from the tropics to mid-latitudes. These meteorological phenomena can bring large amounts of rain or snow to the western United States each year. In locations like California, AR storms are responsible for the largest magnitude […]
DESERT RESEARCH INSTITUTE: Wet soils increase flooding during atmospheric river storms
A new study examined decades of atmospheric river storms across the West Coast to pinpoint the conditions that lead to catastrophic flooding. By the Desert Research Institute Atmospheric rivers are responsible for most flooding on the West Coast of the U.S., but also bring much needed moisture to the region. The size of these storms doesn’t always translate to flood risk, however, as other factors on the ground play important roles. Now, a new study helps untangle the other drivers […]
DESERT RESEARCH INSTITUTE: Flooding in Central Valley offers key opportunities for groundwater recharge
The research used satellite imagery to identify where winter flooding occurs, which can improve flood risk awareness and inform how to best redirect floodwaters to replenish groundwater supplies. From Desert Research Institute: California’s Central Valley — one of the nation’s most critical agricultural regions and home to over 1.3 million people — is prone to flooding. Mapping the extent of winter floods has been challenging for experts, however, because clouds can obscure the view of satellites. Recent efforts to improve […]
NOAA’s atmospheric river research: Serving up data rain or shine
A network of year-round observing stations help meteorologists forecast extreme rainfall events From NOAA Research As the western United States heads into its traditional dry season, water managers are assessing how winter rains have helped replenish the region’s reservoirs. The vast majority of precipitation that falls during the wet season results from atmospheric rivers (ARs) that rain down life-sustaining water but can also cause costly destruction. These fast-moving “rivers” of water vapor in the sky supply up to half of […]
NOTEBOOK FEATURE: From forecast to flow: Optimizing California’s reservoirs with FIRO
California is adapting to increasingly intense storm patterns, largely driven by atmospheric rivers. These narrow bands of concentrated water vapor transport immense amounts of moisture from the tropics, often resulting in heavy rain or snow when they reach land. By utilizing advanced weather forecasting tools and improved monitoring, Forecast Informed Reservoir Operations (FIRO) optimizes reservoir operations to manage runoff more effectively to increase water storage while mitigating flood risks to maximize the performance of California’s existing infrastructure. At the April meeting […]
Click here for all coverage of atmospheric rivers on Maven’s Notebook.