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February 2017: Oroville Dam spillway damaged
A one-two punch of precipitation resulted in damage to Oroville Dam’s main and emergency spillways pushing the second largest dam in California into a crisis in February 2017. Scripps Institution for Oceanography at UC San Diego and their colleagues have released a new report. StudyThey have discovered the climate change fingerprint in the events that triggered it. Issues with the dam’s spillways led to the evacuation of 188,000 people who lived in the floodplain of the Feather River some 70 miles north of Sacramento, Calif.
Though officials narrowly averted a sudden release of water from behind the emergency spillway holding back the top-most portion of California’s second largest reservoir, the incident demonstrates how difficult it is to balance water supply needs served by full dams with public safety that requires retaining sufficient empty space to capture floodwater. According to climate science, precipitation will be less frequent but intense. increasing California’s hydroclimate instability.
“We expect atmospheric rivers (ARs) to become more potent in a warming climate. We had previously evaluated ARs and their contribution to hydroclimate changes over western North America. It was done in global climate model projections,” said study co-author Alexander Gershunov, a climate scientist at Scripps Oceanography, “but this is the first study that quantified the influence of global warming on a specific, real, recent, and impactful atmospheric river event.”
Researchers noted that in summer 2021, Oroville Lake’s record low level prevented hydropower generation for the first time since the dam opened in 1968.
“Climate projections for California and the U.S. West Coast suggest fewer, yet more intense, precipitation events in the future,” said study lead author Allison Michaelis, an assistant professor of meteorology at Northern Illinois University. “Such changes to the hydroclimate naturally come with heightened risks of both drought and flooding and potential for infrastructure damage.”
The research taps into the increasing knowledge of weather phenomena known as Atmospheric riversCalifornia has up toHalf of its annual water supply is now availableAnd account for more than 90 percent of the state’s flood damages. Scripps Oceanography scientists atCenter for Western Weather and Water ExtremesHave been involved in many of the atmospheric river research, including the creation of the AR Scale. This scale categorizes atmospheric storms in a spectrum of beneficial replenishing precipitation events to deluges that can cause widespread floods.
Previous researchScripps Oceanography, which is leading the research, has suggested that the climate will continue to warm and the state and large swathes of the West Coast will become more dependent on atmospheric rivers for water supply. This will make accurate prediction of storms even more important. CW3E scientists are improving their ability to predict when and whereabouts atmospheric rivers will make landfall, and how much rain and snow they will produce.
The new was funded by the U.S. Bureau of Reclamation (DWR) and the California Department of Water Resources AR Program. StudyThe American Geophysical Union journal contains the following: Earth’s Future.
“The potential impacts of atmospheric rivers on water storage facilities were made clear by the 2017 Oroville Dam spillways incident,” said DWR Director Karla Nemeth. “DWR has been working with partners like CW3E and others to enhance tools to better forecast, prepare for, and manage climate change-induced extreme conditions that impact California’s water supply operations.”
An atmospheric river storm made landfall on February 6, 2017 in Northern California. An initial pulse of cold precipitation dumped snow onto an already large snowpack. A warm pulse followed this, which poured rain on top. The second pulse produced similar amounts of precipitation but it had the effect melting the snow on top of the snow, which contributed to the increase in flow that the Oroville Dam was having trouble controlling.
Michaelis, a former postdoctoral research fellow at CW3E and Michaelis, modeled the February 2017 event. The simulation revealed that human-induced global warming caused an 11-percent increase during the first pulse of precipitation and a 15% increase during the second pulse. Researchers found that the warming predicted to occur would have a significant impact on precipitation in the second-pulse. This would have been almost 60%.
However, the first pulse did not experience a significant increase in temperature. The fact that two components of the same atmospheric river event behave differently in simulations indicates that while warmer air can hold more moisture, ARs can be more potent. However, not all ARs are equally enhanced by warming. This complicates weather prediction.
“We were surprised to see such different responses from the two pulses of this storm,” Michaelis said. “The different relationships between warming temperatures and precipitation increases opens up interesting research questions that we’re excited to explore with a larger sample of cases.”
Other than Michaelis and Gershunov the study authors are Tamara Shulgina, F. Martin Ralph of Scripps Oceanography and Meredith Fish, Scripps alumna Meredith Fish and Alexander Weyant. Alexander Weyant was an undergraduate math major at UC San Diego and contributed most of the data analysis. Since then, Weyant has joined Scripps Oceanography to be a first-year PhD candidate.
“I believe most students studying statistics in the math department would find it very exciting to join the research effort on weather events in the background of a nonstationary climate,” said Weyant. “They need only be made aware of this puzzling problem, which straddles the divide between structure and randomness, as well as that of short and long timescales.”
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