DAMSClimate Change Contributor to 2017 Oroville Dam Spillway Incident

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. Researchers from Scripps Institution of Oceanography at UC San Diego and colleagues say in a new study that they have identified the fingerprint of climate change in the events that triggered the incident. 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. The consensus in climate science is that precipitation will become less frequent but more intense, increasing California’s hydroclimate instability.

“We expect atmospheric rivers (ARs) to become more potent in a warming climate. We had previously assessed ARs and their evolving contribution to hydroclimate change 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 increasing knowledge of the weather phenomenon known as atmospheric rivers, which are potent flows of water vapor that provide California with up to half its annual water supply and account for more than 90 percent of the state’s flood damages. Scripps Oceanography scientists at the Center for Western Weather and Water Extremes (CW3E) have led much of the work on atmospheric rivers, including the creation of the AR Scale. The scale categorizes atmospheric river storms in a spectrum between beneficial replenishing precipitation events and deluges that can cause widespread flooding.