Rabu, 05 Agustus 2020

Sea level rise to choke Bay Area traffic as far away as Santa Rosa, Napa, study shows - San Francisco Chronicle


As global warming dials up sea levels and storm surges, the Bay Area will not only see more flooded streets and shorelines, but more traffic, a new study shows, with commuters converging on drier routes and back-ups rippling sometimes 20 miles or more from the water.

The research, released Wednesday by Stanford University scientists, suggests that some of the region’s biggest traffic delays from flooding will be in Santa Rosa, Napa and Vacaville, all far from where the flooding occurs.

In these areas, with water just a foot higher along San Francisco Bay, as many as half of commuters could face back-ups of 30 minutes or more within the next 20 years, the study shows.

The projected delays don’t bode well for a region that’s already socked with congestion. Daily commutes average 30 minutes, and many people drive for much longer to and from work. Shelter-in-place orders during the coronavirus pandemic have provided some relief, but traffic levels already have begun to rebound.

“There’s this common thinking that coastal flooding will only affect residents and businesses in that area” said Indraneel Kasmalkar, a Ph.D. student in computational and mathematical engineering at Stanford and lead author of the new traffic study. “But the disruptions are going to propagate”

These disruptions, the researchers say, are because of the cascading effect of traffic that often makes areas with few major highways, even if they’re far from the trouble spot, more congested.

Some of the worst areas for flooding in the Bay Area are San Mateo and Marin counties, as a result of low-lying bay shore. While Marin County will see the region’s worst traffic delays, according to the study, San Mateo County will have minimal problems because drivers there have more alternative routes.

“If you think about it, it’s not really surprising,” Kasmalkar said. “It’s the road network that really is the key.”

With few options outside of Highway 101 in Marin, more than half of drivers in parts of this county, primarily the San Rafael and Novato areas, will see 30 minute-plus delays with a foot of higher bay water over the next 20 years, the study shows.

Other parts of the North Bay will see an only slightly better traffic situation, also because drivers have fewer ways to get around.

Traffic on Highway 101 through Mill Valley on Aug. 4, 2020 — sea level rise could push traffic inland, making congestion worse, a new study concludes.

The new research, published in the journal Science Advances, does not speculate on how often the nuisance flooding will occur. But climate models show that 12 inches of coastal flooding, which the researchers used as their low-end estimate for projecting traffic delays, will become increasingly common.

Sea levels alone could rise nearly a foot by 2050 with warming temperatures, most models show. On top of that, high tides and big storms, also partly caused by climate change, are expected to push water levels occasionally higher, sometimes much more so.

“If there’s 12 inches of sea level rise and 12 inches of storm surge you’re already at two feet of flooding, and that’s not what you were experiencing before,” said Jessica Fain, director of planning for the San Francisco Bay Conservation and Development Commission.

Fain was not involved in the Stanford study, though her agency’s flood maps were used by the researchers to model what traffic what would look like with higher water levels. The traffic data used for the modeling was from the Metropolitan Transportation Commission and the U.S. Census Bureau. The study focused on commutes in private vehicles during morning rush hour.

The BCDC has done its own evaluations of how flooding will impact Bay Area traffic. The agency’s projections show that 12 inches of higher water will affect 700,000 vehicle trips per day in some way. The analysis focused on areas where the flooding occurred, in contrast to the Stanford study, which looks at the ripple effects beyond.

San Francisco, Santa Clara County and most of the East Bay, like San Mateo County, will experience few delays with a foot of flooding over the next two decades, according to the new study.

With three feet of water, however, which represents a more severe climate scenario but still within the range of expectations, San Francisco, San Mateo County and Santa Clara County will continue to see little additional congestion, the study shows, though commuters in western Alameda and Contra Costa counties will begin to experience significant delays.

Along parts of the the bay shore, some residents won’t even be able to get to work because their route will be cut off with three feet of flooding, according to the study.

Fain, with the San Francisco Bay Conservation and Development Commission, says the potential for huge transportation problems underscores the need for region-wide preparations.

In 2016, Bay Area residents approved a nine-county parcel tax that generates about $25 million annually for restoration projects to help combat rising seas. Efforts to improve more vulnerable transportation corridors, such as Highway 37 in the North Bay, are already under way.

“Maybe San Francisco can build a seawall and Foster City can build a levee, but we need a regional way to coordinate all this,” she said. “You can’t just do it piecemeal.”

Kurtis Alexander is a San Francisco Chronicle staff writer. Email: kalexander@sfchronicle.com Twitter: @kurtisalexander

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August 06, 2020 at 01:25AM

Sea level rise to choke Bay Area traffic as far away as Santa Rosa, Napa, study shows - San Francisco Chronicle



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