For years, scientists have said that atmospheric rivers can make or break the water supplies of California’s thirsty cities and farms.
For the past two winters, there has been a steady flow of these hugerivers in the sky“Dumped the record-breaking and drought prevention Rainfall across the state, as well as catastrophic flood, landslideand dangerous snow storm,
But now, new research shows that these recent atmospheric rivers pale in comparison to some of the monstrous storms that hit ancient California — a sobering revelation that suggests to some experts that such cataclysmic storms could once again hit the state.
“Our findings show that atmospheric river activity exceeds what has occurred since the beginning of instrumental record keeping,” said Clark Knight, a research geographer at the U.S. Geological Survey and lead author of the study. Year. “This is important because it suggests the latent potential for our region to experience storms beyond the ones we’ve seen today.”
Although few people had heard of atmospheric rivers until a few decades ago, research on giant vapor paths has proven vital to California water planning and public safety.
The study’s findings do not bode well for a state whose flood infrastructure was severely strained last year, when a train of atmospheric rivers breached several levees, overflowing and flooding communities. Tulare Lake was once dry, The findings also boost the state’s efforts to capture stormwater as climate change leads to more rainfall fall as rain instead of snow Ushering in a new era of more frequent and prolonged drought.
Knight and his fellow researchers came to their conclusions after analyzing ancient layers of soil from Leonard Lake in Mendocino County. The team was able to determine when more sediment was pushed into the lake, indicating periods of high rainfall.
Then, using the data atmospheric rivers Over the past 60 years, researchers found a “strong correlation” between their sediment findings and modern storms, allowing them to model that link through the rest of the soil layers to reconstruct historical atmospheric river activity, Knight said. Said. his research was Published on Thursday in the journal Nature.
The research provides the most historical context to date for the state’s rainfall variability, and found that the region has experienced “the most frequent extreme rainfall events recorded over a 3,200-year period.”
Biola University students use a rope from a footbridge to stay in position and swim through stormwater flowing through the La Mirada Flood Control Channel after heavy rains caused an atmospheric river at La Mirada Creek Park.
(Alan J. Schaben/Los Angeles Times)
Knight said this new hydrological data could better inform climate modeling and projections, providing a historical record 20 times longer than what is available.
Although the team’s research focused on Northern California – where the most atmospheric rivers are typically seen in the state – they said it is reasonable to conclude that the southern half of the state saw similar atmospheric influences in its ancient climate. Excessive rainfall may have been observed. Rivers.
Previous research has shown that the average atmospheric river transports more than double the flow Of Amazon River. Experts say the possibility of even bigger storms hitting California is worrying.
Daniel Swain, a UCLA climatologist who was not involved in the USGS study, said the paper provides “direct physical evidence” of atmospheric river activity that is more extreme than anything seen in recent California history — dating back to 1862. Even beyond the great flood of 1500 BC, which repopulated the kingdom. landscape.
He said the research “reemphasizes the dangers of assuming that the extremes we saw in the 20th century represent the kinds of extremes possible in this part of the world.”
“It’s a sign that – even if we don’t have to deal with climate change – we should still be vigilant about the risks posed by extremes because we know that the climate system … could throw big, bad things at us.” There is from time to time,” Swain said. “I don’t find that reassuring at all.”
A continued rise in global average temperatures due to humanity’s burning of fossil fuels also threatens to increase cases.
“Adding energy to the system through greenhouse gas emissions is basically like shaking a soda can… and adding a little more energy to the system would have allowed these extremes to be a little more extreme,” said graduate student Cody Poulsen. Is.” researchers at Scripps Institution of Oceanography The Western Weather and Water Extremes Center, which was also not involved in the Nature study.
Swain proposed that Every degree increase in global temperature “increases the risk of”arcstorm Scenario”- A Megaflood event that occurs once in thousands of years, But these new USGS findings may indicate that the worst-case modeling is not extreme enough, he said.
A child walks below Dana Point Falls in March 2023, which only happens when it rains heavily.
(Alan J. Schaben/Los Angeles Times)
For a state that has struggled with frequent and severe periods of drought, the last two wet winters have come as a rare gift. However, many Californians may be surprised to learn that these two wet seasons fall within the range of natural variability. They may also be surprised to learn that there have been more atmospheric rivers this year than last, causing even more damage and disruption.
Recently, researchers have confirmed that 51 atmospheric rivers hit the west coast during the 2023-24 rainy season – significantly more than the 38 atmospheric rivers expected during the 2022-23 rainy season. According new data From the center of western weather and water extremes.
In California in particular, 44 atmospheric rivers descended from October to March, up from 31 during last year’s rainy season, said Chad Hecht, a meteorologist at the center.
But even though there were more atmospheric rivers this rainy season, fewer storms were measured as strong or extreme on the Center’s strength scale than in the season before that.
“It’s not quantity, it’s quality,” Hecht said.
For example, 12 intense, extreme or extraordinary atmospheric river storms Hits California between October 2022 and March 2023. These heavy storms bring news-making rain and snowfall. However, this season, only five were recorded in the state.
“If you compare it to last year, … this (water) year has had some strong storms, but it’s been very weak,” Hecht said. “But the abundance of weak-to-moderate (atmospheric rivers) helped keep us on the trajectory to reach that normal (precipitation level).”
As of this month, the record Both statewide rainfall And this snow cover in the sierra nevada That was about 105% of average for this time of year — which Hecht said was surprisingly close to average.
“This year was unusually normal,” Hecht said. “We like to talk about California being the land of extremes, where it’s either extremely dry or extremely wet. This year was unusual because it was very close to normal by April 1,” the date that typically marks the end of California’s wet season.
However, Southern California has seen slightly higher odd water yearAccording to California Water Watch, annual rainfall in many coastal areas is more than 140% above average.
Hecht said that a strong, slow-moving atmospheric river in early February had an extreme impact on the region’s precipitation, and he noted that many areas were also hit by storms that he described as “highly productive” weaks. Atmospheric river storm was called.
Systems do not typically occur with thunderstorms, but there were several systems this season, causing locally historic rainfall and flash flooding in many areas, including San Diego And oxnard,
Hecht said it’s not immediately clear why so many atmospheric rivers are involved in storms this season, but he said higher sea surface temperatures — a signature of the El Niño weather pattern — help promote unstable convection patterns. Can do.
Despite numerous water measurements pointing to a below average water year so far, federal officials recently released a major disaster declaration For nine counties after Fatal February atmospheric river storm.
Knowing that further extreme rainfall is possible, Swain said he hopes state officials can better prepare for emergencies, or at least better understand the potential risks.
“If we don’t estimate the risks correctly at the outset … it is very difficult to have an accurate discussion about the costs and benefits of a particular intervention,” Swain said.
But, he said, climate change is still likely to exacerbate those natural extremes.
Swain said, “It’s fair to interpret the 20th century as being really lucky in California, in the sense that we didn’t see anything worse … just through random, natural variability.” “twenty first century? This is a massively loaded die.”
