Atmospheric Rivers (ARs) are relatively narrow regions in the atmosphere that are responsible for most of the horizontal transport of water vapor outside of the tropics.According to some daunting new reports, atmospheric rivers were responsible for the mysterious die-off of wild Olympia oysters in San Francisco Bay in 2011. This marks the first document case of ‘rivers in the sky’—which can hold 15 times more water than the Mississippi River and cause direct harm to an entire population. Now, scientists predict they will only increase in frequency, intensity, and unpredictability as the global climate continues to change.
Here are some quick facts!
- On average, about 30-50% of annual precipitation in the west coast states occurs in just a few AR events, thus contributing to water supply.
- In the strongest cases ARs can create major flooding when they make land-fall and stall over an area.
- ARs are a primary feature in the entire global water cycle, and are tied closely to both water supply and flood risks, particularly in the Western U.S.
- A well-known example of a type of strong AR that can hit the U.S. west coast is the “Pineapple Express,” due to their apparent ability to bring moisture from the tropics near Hawaii to the U.S. west coast.
- A strong AR transports an amount of water vapor roughly equivalent to 7.5–15 times the average flow of liquid water at the mouth of the Mississippi River.
- On average ARs are 400-600 km wide.
- ARs move with the weather and are present somewhere on the earth at any given time.
- Improved understanding of ARs and their importance has come from more than a decade of scientific studies using new satellite, radar, aircraft & other observations & major weather model improvements.
Researchers concluded these rivers are responsible for the first mass die-off event, when a population of about 3,000 Olympia oysters per square meter suddenly disappeared in March 2011. That is not only a problem for the oysters. They are filter feeders that can clean up to 30 gallons of water a day, removing excess nitrogen and other pollutants from the environment.
“In March 2011, a series of atmospheric rivers made landfall within California, contributing an estimated 69.3 percent of the precipitation within the watershed, and driving an extreme freshwater discharge into San Francisco Bay,” the research team concluded. “This discharge cause sustained low salinities…that almost perfectly matched the known oyster critical salinity tolerance.”
The researchers report that the population has been recovering since the extinction, but they will likely never be able to restore the numbers they once had. They believe similar local extinction and mass mortality events could be on the horizon as climate change increases the frequency and severity of the weather.
This prediction is backed by NASA, whose satellites have shown an increase in large, well-organized thunderstorms. Rainfall increases have been reported in the western Pacific and are due to large storms picking up the frequency. While climate models have long predicted that a warmer climate will cause an acceleration of the water cycle, models have not yet produced this change in the frequency NASA has witnessed.
Atmospheric rivers are narrow regions in the atmosphere that are responsible for most of the horizontal transport of water vapor outside of the tropics. They range from 400 to 600 km wide and can deliver up to half California’s annual precipitation in just 10 to 15 days. While most of these rivers are mild, they can create extreme rainfall and floods—leading to mudslides and drops in salinity. They have been linked in major floods in California—and all 10 of Britain’s largest floods since the 1970s.
“Extreme events are predicted to be more prevalent under climate change,” a research team at the University of California, Davis reports. “We highlight a new mechanism by which precipitation extremes appear to affect a sensitive species, contributing to the near 100 percent mass mortality of wild oysters in northern San Francisco Bay.”