A good article about them from the Washington Post.
“At the Center for Western Weather and Water Extremes, researchers feel the urgency as they examine connections between West Coast precipitation and a devastating wildfire season, which has yet to conclude.
“The center, part of Scripps Institution of Oceanography in La Jolla, Calif., has unlocked many secrets of atmospheric rivers — airborne jets of tropical moisture that can break droughts and quell fires but also unleash raging floodwaters.
“Under the leadership of Director Marty Ralph, the center measures the strength of atmospheric rivers on a one-to-five scale, and there is now a greater understanding of how their presence or absence determines so much, such as whether vegetative fuels will be primed to ignite when fire comes too close.
“It’s been an exciting time,” Ralph said. “I mean, there’s so much potential for better weather prediction on the West Coast … to impact decisions that matter.”
“But looming in the background of this important research are the reports from Ralph’s friends and colleagues across the West who have been severely affected by the siege of blazes. “It’s been tragic,” he said.
“Climate scientist Dan Cayan, who works with Ralph, added: “The [fires’] different impacts and symptoms certainly keep us in touch with reality, and underpin the need for the sort of work we do.”
“California has seen its worst wildfire season on record in 2020, with about 4.2 million acres burned, more than double the acreage in the previous record-breaking year.
“The work done by the center has revealed just how crucial atmospheric rivers are to California, which is both the most populous U.S. state and the country’s top agricultural producer. These phenomena deliver 25 to 50 percent of the water supply in key areas, with tens of billions of dollars in annual benefits. But atmospheric rivers also contribute to more than 90 percent of the region’s major flood events, at an average cost of $1 billion per year.
“It’s just remarkable how that one concept can explain a lot of the action in the Western United States,” Cayan said.
“With Sept. 30 marking the final day of the 2019-20 water year, a look at recent history turns up evidence of the ties between atmospheric rivers and ripe conditions for wildfire.
“During the 2018-19 water year, California saw the landfall of 36 atmospheric rivers, with seven of those considered strong or greater (Category 3 and above). But in the 2020 water year, the Golden State saw 20 percent fewer atmospheric rivers (29) — and there was just one strong atmospheric river event.
“For the entire West Coast, the 2019 water year experienced 41 atmospheric rivers, 11 of them strong, while the water year 2020 experienced 40, with seven strong.”
Retrieved December 6, 2020 from As fires rage, California center aims to better understand atmospheric rivers – The Washington Post