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How the next wave of Bay Area superstorms could be the most devastating yet

Flash flood warnings for parts of the East Bay as rivers rise

By Alissa Walker
A sign warns motorists of flooding on northbound Highway 101, Monday, Feb. 20, 2017, in Corte Madera, Calif. Heavy downpours are swelling creeks and rivers and bringing threats of flooding in California's already soggy northern and central regions. The Na
A sign warns motorists of flooding on northbound Highway 101 in Corte Madera.
Photo by AP Photo/Eric Risberg

Over the last few weeks, the storms slamming California have delivered devastating floods, heavy winds, “weather bombs,” and a near-disaster at one of California’s largest reservoirs. But the next atmospheric river superstorm to sweep across the state could be the most dangerous in decades.

Today’s storm is a particularly wet, slow-moving system in a string of atmospheric river events—the “fire hose that funnels moisture from the tropical Pacific towards California”—which have saturated the ground and pushed stream flows to historic limits.

The National Weather Service is warning residents of the Sacramento region and some inland areas of the Bay Area to be ready to evacuate at any time. Over 100 flights have been canceled out of SFO as of 11:30 a.m. In the East Bay, residents need to watch for the flooding of creeks and other small urban waterways. (Check out this interactive flood map for live updates.) The heaviest rain will arrive this afternoon and could bring up to four inches to the area.

Major rivers which supply the city with water are also experiencing dangerous flooding. The San Joaquin and Sacramento Rivers, for example, are the main tributaries of the California State Water Project, the hub which provides drinking water to 23 million of California’s 39 million people.

What’s of greatest concern today is the potential breach of the California Delta levee system, which would contaminate the state’s freshwater supply with flooding sea water. This is what’s called saltwater intrusion, and it’s the worst possible thing that could happen to the state’s water supply, according to meteorologist Eric Holthaus:

The implications of this flood would be huge: If the levee system is breached, Sacramento could have 30 feet of flooding, and much of the state's water delivery system could be paralyzed by an influx of saltwater, including much of southern California. Two-thirds of people in the state could lose fresh water. That's not to mention the potential loss of life. Of course, this is not a given based on the latest weather forecast—but the fact that it can't be ruled out should cause everyone in the region to pay close attention.

California scientists have been preparing the state for this kind of flooding thanks to the ARkStorm scenario, a fictional atmospheric river-powered flood based on the actual events of a winter storm event that happened 155 years ago:

From December 1861 to January 1862, it rained for 45 straight days in California. The Great Flood of 1862 wrought so much destruction that some parts of the state remained underwater six months later. The center of California turned into a 300-mile sea.

Finance-wise, the storms “bankrupted the state, destroyed the ranching industry, drowned 200,000 head of cattle [and] changed California from a ranching economy to a farming economy” in essentially one stroke, seismologist Lucy Jones told NPR in 2013.

Downtown Sacramento flooded in 1862—and it could happen again

Even if the state got 45 days of rain in 2017, what happened in 1862 is unlikely to happen again today, thanks to a century and a half of building infrastructure to protect California’s cities. What the information from the ARkStorm Scenario can do is take the 1862 flood and reimagine that event in light of current climate trends. A hotter planet means warmer, more moisture-saturated air, which means atmospheric river events like this will be the norm in the future. California’s infrastructure was built under the assumption that events like this were more rare than they’re turning out to be, and that infrastructure might not be able to withstand the new normal.

That’s the reason why the climate research being performed right here in the state is more valuable than ever: USGS, NOAA, and NASA are working together to bring real-time updates on the storm and how it will impact dams, reservoirs, and aqueducts. This helps California officials make quick decisions about how to move water around the state. But for a storm like this one, it’s more than just making sure that California’s residents will have uninterrupted access to a clean, safe water supply. Today, that science will more than likely save lives.