California's Future Weather Will Alternate Between Drought and Atmospheric Rivers, Study Sayshttps://www.sfgate.com/weather/article/Atmospheric-river-drought-Calif-weather-Scripps-14083031.phphttps://www.wired.com/story/atmospheric-rivers-get-an-intensity-scale-like-hurricanes/Coefficient of variation (i.e. variance normalized by the mean) of de-trended* annual total precipitation during historical (a) and future (b) time periods in the Real-5 LOCA-downscaled GCM ensemble average, and the difference (c).The study, published Tuesday in the journal
Nature Scientific Reports, looked at climate scenarios from 16 global climate models focusing on western North America. All 16 predicted that most of the heavy precipitation that the West receives in the future will come from the vast streams of moisture in the sky known as atmospheric rivers. A single atmospheric river typically carries twice the amount of water flowing in the entire Amazon River.
"As Mediterranean climate regions around the world are becoming more subtropical, the dry season is expanding. California is no exception," Scripps climate scientist and study lead author Alexander Gershunov said. "What is exceptional about California is that the heavy precipitation is projected to become more extreme."
Here's what scientists expect to happen:
—Overall precipitation will be about the same or slightly more over the long term. But it will progressively become more dramatic — more will fall in extreme bursts, increasing the possibility of flooding. Daily precipitation will become less frequent as there will be fewer storms not related to atmospheric rivers (ARs).
—California will not be able to rely on mountain snowpack to portion out water from melting snow. Because atmospheric river storms are warmer, snow levels will be higher. Driving rain will wash away snowpack at lower elevations. As the Sierra Nevada acts as a barrier to easterly moving storms, "California's topography is ideally aligned to extract increasingly heavy precipitation from strengthening ARs," the study said.
—Due to the unpredictability of snowmelt, resource managers may have to overhaul the state's water storage procedures. So far this century, there have only been four wet years — 2005, 2011, 2017 and 2019. In 2015, amid California's five-year drought, the Sierra Nevada received only 5 percent of its normal snow accumulation.
—Periods of drought will become more numerous and lengthy, but California is not projected to dry as severely as other Mediterranean climate regions around the world.
—The state will experience a feast-or-famine rainfall scenario — drought vacillating with flooding.Open Access: Alexander Gershunov,et.al.,
Precipitation regime change in Western North America: The role of Atmospheric Rivers,
Scientific Reports volume 9, Article number: 9944 (2019)
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Never Mind Those Earthquakes: Atmospheric Rivers Could Put Sacramento 30 Feet Under Waterhttps://www.sacbee.com/news/local/environment/article232426112.html
A research team led by Sasha Gershunov at Scripps Institution of Oceanography at UC San Diego published a new study on atmospheric rivers in
Nature Scientific Reports this week that places atmospheric rivers under scrutiny as the driving cause behind California’s increasingly extreme, infrequent bouts of precipitation.
Gershunov’s team used 16 global climate models to analyze the expanding role of atmospheric rivers as contributors to precipitation in California. The results show that atmospheric rivers are getting stronger and wetter, and catastrophic events like the Great Flood of 1862 could happen again.
“In 1862, Sacramento was underwater,” Gershunov said. “It was most certainly due to an atmospheric river.”
In 1861, Northern California became the focal point for two consecutive atmospheric rivers that surged into the Sierra Nevada, melting snow at disastrous rates. By 1862, a catastrophic flood swept through the Central Valley, augmented by two rainstorms, creating an inland sea that was 300 miles long and 60 miles wide.
It rained for 45 days straight, according to a film produced by the U.S. Geological Survey. Thousands of cattle drowned, and vineyards and homes were washed away. The state went bankrupt. The American River near Auburn rose 35 feet, submerging towns.
No place was more affected than Sacramento, however.
Situated at the confluence of the American and Sacramento rivers, the city went under 30 feet of water.
Leland Stanford, the governor-elect, had to row a boat to his inauguration in January 1862.
“Nearly every house and farm over this immense region is gone. America has never seen such desolation by a flood,” wrote botanist William Brewer of the California Division of Mines and Geology in 1862.
According to a team led by scientist Dale Cox at the U.S. Geological Survey, California is due for another megaflood.
“Absolutely, it could happen again,” Gershunov said. “The probability of it happening is increasing with stronger atmospheric rivers.”