More of the Bay Area Could Be Underwater in 2100 Than Previously Expected
By TROY GRIGGS MARCH 7, 2018, The New York Times
The ground around San Francisco Bay is sinking to meet the rising sea, another reason for Bay Area residents to worry about the impact of climate change on their region.
A new report suggests that sinking land, known as land subsidence, will increase the potential reach and damage of flooding in the Bay Area, submerging a larger portion of the region by the year 2100 than previously estimated.
Subsidence can be caused by groundwater pumping, which can act to “deflate” the ground above it or the gradual compacting of landfill — when lands are filled in an effort to create solid ground to build upon.
The authors of the report — Manoochehr Shirzaei, a professor at Arizona State University and Roland Bürgmann, a professor at University of California, Berkeley — have combined land elevation data with rising sea level projections. And they are now challenging the current flood threat projections as too conservative.
The authors hope that their new findings will help cities and agencies produce more accurate hazard maps, updating the extent of affected areas.
Under the new projections, San Francisco International Airport could see half of its runways submerged by the year 2100. Original estimates that did not include land subsidence were much lower. Other areas around the Bay that have been built on engineered landfill, like parts of Foster City and Treasure Island, are particularly vulnerable to the dual impact of subsidence and sea level rise.
The combination of rising sea levels and sinking ground increases estimates of the total amount of endangered areas to a range of 48 to 166 square miles. The rate of sink plays a role in the severity of the estimate: While most areas around the Bay are sinking at less than two millimeters per year, some have been found to be sinking at a rate as high as 10 millimeters per year.
Dr. Shirzaei said that the new estimates take into account a range of outcomes, from a “best case scenario” of sea level rise — assuming countries follow the 2015 Paris agreement for emissions reduction — to more extreme cases, where the sea level rises faster because of an accelerated melting of Antarctic ice. At the more severe end of the spectrum, the level of flooding would far exceed the effects of sinking land.
Scientists have long tracked the effects of global warming on the planet’s water levels. A recent study of 25 years of satellite data pointed to climate change as a cause for the acceleration of rising sea levels, making previous estimates unreliable.
“It’s a very well-known problem, but we really don’t know how fast it’s going to be in the second half of the 21st century. This is a projection,” Dr. Shirzaei said.
Additional work by Tim Wallace, Matthew Bloch and Jugal K. Patel.