Climate change was identified as a contributor to the 2017 Oroville Dam Spillway Incident

A two-punch of precipitation led to damage to Oroville Dam’s main and emergency spillways. This put the second largest dam in California in crisis. In a new study, Scripps Institution for Oceanography at UC San Diego researchers and their colleagues have found the climate change fingerprint in the events that triggered this incident. 188,000 people living in the floodplains of the Feather River 70 miles north from Sacramento, Calif. were evacuated because of spillway problems.

Officials narrowly avoided a sudden release from water behind the emergency spillway that held back the top-most part of California’s second-largest reservoir. However, the incident shows how difficult it can be to balance water supply needs served through full dams with public safety which requires sufficient empty space to capture floodwater. The consensus was in climate scienceThe result is that California’s hydroclimate instability will increase as precipitation becomes less frequent and more intense.

“We expect atmospheric rivers to become more powerful in a Climate change. We had previously evaluated ARs and their contribution to hydroclimate changes over western North America. It was done in global climate models projections,” said Alexander Gershunov (climate scientist at Scripps Oceanography), co-author of the study. “But this is the first study to quantify the impact of global warming on a specific and recent, significant atmospheric river event.”

Researchers found that the dam’s opening in 1968 had prevented hydropower generation at Oroville Lake for the first summer in 2021.

“Climate projections of California and the U.S. West Coast suggest that there will be fewer, but still more intense, precipitation events in future,” said Allison Michaelis (study lead author), an assistant professor of meteorology from Northern Illinois University. “Another consequence of such changes in the hydroclimate is increased risks of drought and flooding, and potential infrastructure damage.

This research taps into growing knowledge about the weather phenomenon known asAtmospheric riversCalifornia is blessed with a number of potent water vapor flows, such as the.Half of its annual water supply is now availableAndMore than 90 percent of flood damages in the state can be attributed to them. Scripps Oceanography scientists at Center for Western Weather and Water Extremes, (CW3E), have been leading much of the research on atmospheric rivers. This includes 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 state and much more of the West Coast will become increasingly dependent on atmospheric river for their water supply as the climate warms. This will make accurate prediction of storms 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 study was funded by the U.S. Bureau of Reclamation and the California Department of Water Resources (DWR), which is published in the American Geophysical Union journal. The Future of Earth.

“The potential effects of Atmospheric riversDWR Director Karla Nimeth said that water storage facilities were highlighted by the 2017 Oroville Dam leakways incident. “DWR has been working closely with partners like CW3E to improve tools to better forecast, prepare, and manage extreme climate conditions that could impact California’s water supply operations.”

On February 6, 2017, an atmospheric storm made landfall in Northern California. An initial pulse characterized by relatively low precipitation dropped snow on an already large snowpack. The snow was then covered by a warm pulse, which poured rain onto the snow. Although the second pulse produced the same amount of precipitation as the first, it had the effect that it melted the snow on the ground and contributed to the inflow that Oroville Dam had difficulty controlling.

Michaelis, a postdoctoral research fellow at CW3E, led the modeling of the February 2017 event. The simulation showed that human-induced warming caused an increase of precipitation by 11 percent during the first pulse, and a 15 percent increase in the second pulse. The researchers estimated that precipitation in the second pulse would have increased by almost 60 percent by the end of the 21st century.

The first pulse however did not see a similar 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.

Michaelis stated, “We were shocked to see such differing responses from both the two pulses in this storm.” “The differences in precipitation and warming temperatures opens up interesting research questions, which we are excited to explore with a larger number of cases.”

Neben Michaelis und Gershunov are Tamara Shulgina of Scripps Oceanography sowie F. Martin Ralph, Scripps alumna Meredith Fish (study authors), and Alexander Weyant. Weyant was an undergraduate math student at UC San Diego. Weyant joined Scripps Oceanography in January as a first-year Ph.D. candidate.

Weyant said that he believes most students who study statistics in the mathematics department would find it very interesting to join the research effort on weather events against the background of a nonstationary environment. “They should only be made aware that this puzzling problem straddles both structure and randomness and short and long-term timescales.