Climate change and land subsidence pose threat for coastal Bay Area

The Bay Area is sinking and climate change is speeding things up, according to a new study published in Science Advances this month.

The study was conducted over the span of two years by researchers Manoocher Shirzaei and Roland Burgmann, who used satellite images to evaluate regions of the Bay Area, such as Treasure Island, which are experiencing sea level rise because of the accelerated melting of polar ice. Shirzaei is a former UC Berkeley post-doctoral student, and Burgmann is a professor in the university’s earth and planetary sciences department.

“What we concluded is that sea level rise is happening, and as a result of sea level rise costal cities will be flooded,” says Shirzaei, who is currently a professor at Arizona State University in the School of Earth and Space Exploration. “The second conclusion is that coastal areas are subject to land subsidence, and those areas are at greater risk of flooding.”

Subsidence, or the caving of land, has always been a problem for coastal parts of the Bay Area, where empty pockets of earth that were once filled with plant matter and water are now dried up and collapsing. And now the problem is growing worse.

“Sometimes global climate change causes droughts, and as a result of droughts people start using water, and the more you extract water—the more it causes subsidence. So there is an indirect relationship because global climate change and land subsidence,” Shirzaei says.

As sea levels rise thanks to polar melt caused by global climate change, the water washes over costal lands. Meanwhile, the ground beneath is already slowly sinking. Together, this increases the risk of flooding for Bay Area coastal areas.

“By 2030, there will be areas that’s physically underwater,” Shirzaei says. He says an official report will released by the Union of Concerned Scientists (UCS), an American-based non-profit science advocacy organization, at some point in the future. 

The increase in subsidence rates due to climate change may not pose any immediate danger for now, as most the Bay Area landscape continues to visibly remain above sea level. The average rate of subsidence noted in the study was less than 2 millimeters per year.

But there’s a catch: many areas of the Bay Area are more vulnerable. Instead of being built on bedrock, many were built on sand and landfill. Take the Barbary Coast in San Francisco. Most of the coast was built on the wooden planks of old, abandoned ships left on bay waters by settlers who came in search of gold. Or San Francisco airport, which is projected to be fully submerged in water by 2100 based on Shirzae’s study which indicates subsidence rates “exceed 10 mm a year in some areas underlain by compacting artificial landfill and Holocene mud deposits.”

But East Bay residents like David Lewis, the executive director from the organization Save the Bay, based in Oakland, says more can be done to combat quickening subsidence rates in the Bay Area. He believes the Federal Emergency Management Agency (FEMA), a government agency which responds to disasters in the US, has not kept up on collecting data to update the Bay Area’s flood maps, and that researchers’ skepticism about climate change effects what the public knows about the impact of future flooding.

“When FEMA does update the maps they are not actually including the risk of flooding increasing over time because of climate change,” Lewis said. “Because of the failure of government agencies to update the maps, a lot of people living in risky areas don’t know it.” 

Lewis and his organization led an effort in 2016 to raise half a billion dollars in local funding for a tidal marsh restoration project. A nine-county vote established a new parcel tax of $12 a year for landowners to fund the restoration project. In this case, the restoration project is aimed at rebuilding “green infrastructure,” such as marshlands, which protect and restore California’s natural water cycle. “Those marshes actually adjust to changes in sea level rise,” Lewis said.

The project is underway with the current restoration of 35,000 acres of acquired land stretching south of the San Mateo Bridge and north of the Dumbarton Bridge, an area greatly affected by subsidence. Lewis is certain if the Bay Area cities don’t act quickly to fund more types of these restoration projects to protect the coastline, the damage done will cost more in the long run.

Shirzaei says the good news is that the data from his study, which highlight areas affected by climate change and land subsidence, will be provided to FEMA, which is using it to update flood maps for the Bay Area. 

Although the effect of climate change and land subsidence in the Bay Area is for now mostly a series of future projections, in some parts of the Bay Area, building on a faulty foundation is already proving to have severe consequences. The Millennium Tower, constructed on piles of dense mud in 2008, is slowly starting to lean and sink. But unlike the Tower of Pisa, the owners have wasted millions of dollars ($750 to be exact) to slowly inch their way to the bottom. The owners of the tower “insisted the foundation was fine” although “nearby construction at the Transbay Transit Center, which included pumping out groundwater, led to softening and compressing the soil,” according to a November 7th, 2017 article by Forbes reporter Julie Littman.

The Bay Area isn’t the only area sinking more quickly because of climate change. In New Orleans, the subsidence rate for costal regions is up to 8 to 10 millimeters a year, according to a study which links subsidence rates to climate change conducted in 2017 by environmental scientists at Tulane University for the Geological Society of America.

The study indicates that “the fundamental culprit” of Louisiana’s wetland loss is the construction of flood-protection levees, which have increased subsidence rates. Researchers write that the problem is likely to “worsen in the future due to limited sediment loads and accelerated sea-level rise.”

After Hurricane Katrina, Army Corps engineers built the “Hurricane and Storm Damage Risk-Reduction System” in New Orleans. A floodwall surrounding the city that cost $14.5 billion is meant to serve as a resident’s protection against the rising tides of another hurricane.

“The issue is that the floodwall or seawall land is going to subside like every other infrastructure near the coast,” Shirzaei said about New Orleans. “So, you have to keep increasing the height of the seawalls. It’s like an open-ended investment.”

Flood levels are not the only factor that effect land subsidence. When farmers drain aquifers to water crops, nutrients become depleted from the soil, causing the land to turn dry and cave in. The Bay Area’s history is marked by attempts to stay afloat, with the construction of canals which redirected the need of farmers to suck water up from the under the ground. According to available figures published in 1998 in the East Bay Plain Beneficial Use Study from the Water Board of California, by the 1930s “nearly half of the ground was pumped from well fields stretching from southeastern end of Alameda Island through the Oakland Coliseum to 98^th Street. The San Pablo wells supplied water to Richmond, but they were over pumped and shut-down twelve to fifteen years after being drilled.”

In attempts to counteract the issue of farmers stealing groundwater from the drought-riddled aquifers, canals were established in the East Bay. But the Contra Costa Canal between Oakley and Concord, built 82 years ago, is now is cracked, and crumbling from subsidence damage and in need of a $400 million development, according to the Contra Costa Water District Ten- Year improvement Plan published in 2016.

In New Orleans, city planners attempted to solve the problem of farmers draining aquifers to water crops by developing 40 miles of canals. Ultimately the canals weakened the foundation of the city, worsening the issue, and the city continued to drop, nearly half of it dipping below sea level by the 1960s, according to Tulane geographer Richard Campanella in his February piece for The Atlantic, “How Humans Sank New Orleans.”

East Bay researchers are trying to prevent the same poor planning mistakes seen in New Orleans, with the establishment of teams of innovative organizers called “Resilient by Design,” who have created a collaborative challenge of bringing experts together to find solutions, creating a solid landscape that can stand the rising floodwaters and sinking land. Collectives like Common Ground in San Pablo, Home Team in North Richmond, or Team Uplift in Vallejo, are developing unique solutions to combat the issue of subsidence and climate change, given the Bay Area’s unique geography.

But still, Shirzaei says the effect of climate change on these vulnerable, costal regions of the Bay Area poses the need for immediate solutions because the study is a conservative estimate of flood hazard, and the actual flood hazard is going to be much bigger.

“We know all the facts—the problem is the issue of how to stop sea level rise, and stop land subsidence,” Shirzaei said. “That’s going to be a big challenge and a costly one.”