California Floods

Flood waters from the Russian River flood Guerneville, on Feb. 28.

Climate change through the rest of the 21st century could be much more threatening to coastal California than previously anticipated, based on newly published research led by the U.S. Geological Survey.

The new numbers are dramatic: Dynamic flooding in California could total more than $150 billion in property damage and impact about 600,000 people by the year 2100, according to research. When factoring in population trends, extreme scenarios could increase the total number of affected Californians to more than 3 million.

The research focuses on long-term sea-level rise using a new model that accounts for changes in things like tides, storms and beach/cliff erosion, according to material published Wednesday in the journal Scientific Reports.

The study notes exposure to flooding is “amplified during episodic storms,” including El Niño events along the West Coast, like the one Northern California experienced recently.

Using static modeling, which does not account for changing tides over the next 81 years, previous research expected 200,000 Californians to be affected by rising sea level and the floods that will come with it.

“These results highlight the importance of including climate-change driven dynamic coastal processes and impacts in both short-term hazard mitigation and long-term adaptation planning,” the report’s abstract concludes.

The new research projects the global sea level to rise as much as 6 feet.

Researchers used a physics-based system, the Coastal Storm Modeling System (or CoSMoS) to adjust sea-level projections for dynamic water levels.

Even a foot or less of rise from current sea levels could “overwhelm” sensitive areas if risks are not adequately mitigated, the USGS says.

“(M)illions of California residents live in or immediately adjacent to low-lying coastal areas and urbanized estuaries, within several meters of present-day sea level,” the study’s results section says. “... These vulnerable coastal settings often contain important infrastructure, such as airports and ports, which are shown here to be vulnerable to future SLR (sea level rise) and extreme storm conditions.”

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About 95 percent of California’s coastal population lives in the Bay Area and Southern California’s urban hubs, the Los Angeles and San Diego areas.

“Furthermore, the alarming scale of these impacts does not account for the ripple effects such extreme events have across economic sectors such as those related to closures of ports, disruption of transport of goods and services, business closures, and impairment of utilities both today and into the future,” the study says.

Central Valley Flood Protection board member Joe Countryman said sea-level rise — even as much as 3 feet — would not likely have a direct impact on Sacramento’s levees, but “would impact the Delta for sure.”

“For the most part, if you take some place like Sacramento, our levees are like 25 feet high,” he said. “So if you get a 3-foot rise in sea level, it doesn’t really affect the levees this far inland.”

However, Countryman said findings from state’s flood research plan in 2017 showed that flood magnitudes could increase by 10 to 20 percent along the Sacramento River basin over the next 50 years, and “maybe a lot more” in the San Joaquin River basin.

In a news release accompanying the new model’s findings, USGS says the research is already being used to help coastal managers plan hazard mitigation efforts. Agencies charged with risk mitigation include the Department of Defense, Caltrans, National Oceanic and Atmospheric Administration, California Department of Emergency Services, national parks and all major cities and counties statewide.

The study says some of the most critical hazard mitigation efforts will include infrastructure improvements to seaports, airports and coastal roadways.

Countryman further explained how climate change affects not only sea levels along the coast, but inland flood risk.

“Storms would be warmer, whereas now a lot of (California’s) precipitation falls as snow. A lot more of that would be rain, so it would significantly increase the runoff.”

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