Photo: AP

If you think the housing crunch is bad in the Bay Area now, just wait. New findings show that more land is sinking into San Francisco Bay than previously thought. Factoring that along with sea level rise projections means even more real estate in harm’s way.

The research, published in Science Advances on Wednesday, uses high resolution satellite and aircraft data to reveal that the Bay Area is in dire straights. The analysis shows we’re currently underestimating the amount of land that could be flooded by 2100 by up to 90 percent. It seems like something local officials might be interested in!

“Knowledge of where the ground in the Bay Area is sinking, and by how much, is not included in the official planning maps that authorities use to assess the local flooding risk from rising sea levels,” Manoochehr Shirzaei, a remote sensing researcher from Arizona State who led the study, told Earther.

Sea level rise alone would increase the risk of flooding along 20 to 160 square miles of coastline by 2100 depending on how much more carbon pollution we emit. Under a best case scenario, that rise could be about 16 inches, though it could reach up to 39 inches if emissions continue on their current trend. None of those estimates include collapsing land, though, and the new research shows the area inundated around San Francisco could balloon to 48 to 166 square miles when subsidence is factored in.

Policymakers and scientists have known for years that parts of the Bay Area are sinking. Large deposits of mud from the Holocene support some shoreline developments while other areas like Treasure Island, a San Francisco neighborhood that sits in the middle of the bay, are built on landfills. Unlike firm bedrock, these areas are being compacted by their own weight.

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A snapshot of parts of the Bay Area that will see some of the worst inundation of subsiding land plus sea level rise. The top row shows subsidence alone, the middle row shows sea level rise alone and the bottom shows the impacts of both together.
Graphic: Shirzaei and Burgmann, 2018

What’s new in Shirzaei’s research is high resolution data that allowed him and his colleague to identify hot spots of subsidence. They found some areas are sinking at a rate of as much as four-tenths of an inch per year. That includes crucial infrastructure like San Francisco Airport, which saw nearly 56 million passengers pass through last year.

Subsidence also puts underserved communities at risk. These include Union City, an East Bay city. According to maps published by research and journalism nonprofit Climate Central, areas that will experience the twin terrors of subsidence and sea level rise will hit a region with particularly high levels of social vulnerability.

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That presents city planners with twin challenges of protecting infrastructure that makes the economy hum along, and citizens who have already been dealt a raw socioeconomic hand. It could be a case for the state’s new Bureau of Environmental Justice.

The findings also offer a blueprint for analyzing other cities built on shaky geological footing. Because a number of the world’s megacities were built in similar environments at the mouth of rivers to facilitate trade, that includes a lot of places (and people).

“As a part of NASA Sea Level Change team, we are planning to do similar study for the entire coast of U.S.,” Shirzaei said.

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And with satellites circling the globe providing this data for other areas, it’s possible a global review could be done down the road. With sea level rise slated to accelerate throughout the century, the results can’t come soon enough.