Depending on the magnitude of sea level rise over the coming decades, between three and six percent of Bay Area residents may be vulnerable to rising tides. While this is just a small share of the region’s population, the impacts to these communities may be dramatic, with broader consequences felt beyond these communities’ borders from impacts to infrastructure and other regional assets. If sea level rises just 12 inches above today’s levels – 194,000 residents will be regularly inundated. Looking at historical growth patterns since 1990, the share of the region’s population living in inundated zones has remained relatively steady. This indicates that new housing developments are occurring at the same rate in areas at risk from sea level rise as in the region overall.
Vulnerability to Sea Level Rise
Vulnerability to Sea Level Rise
As a result of global climate change caused by greenhouse gas emissions, sea levels are expected to rise over the coming decades. Despite the region’s commitment to reducing these harmful emissions, the Bay Area is not immune to this global trend that may seriously affect low-lying coastal areas across the world. Understanding which neighborhoods are most vulnerable from rising tides should help the region set key priorities when it comes to local and regional resilience planning, adaptation and future growth patterns.
The unique geographical features of each Bay Area county – combined with the location of existing residential developments – have a strong influence on the number of residents who may be vulnerable to future sea level rise. Residents in Marin County, with much of its population clustered in low-lying areas bordering the Bay shoreline, are the most at risk. Approximately 28 percent of Marin’s population is expected to be exposed to inundation by a four-foot rise in tides. Even when sea level rise reaches just 12 inches – a likely forecast for 2050 – almost one in five Marin residents would still be affected. The situation is only slightly better in neighboring Solano County and further south in San Mateo County, with similarly low-lying communities by the Bay such as Vallejo, Redwood City and East Palo Alto.
While existing neighborhoods in San Francisco would not be significantly affected by sea level rise below 2 feet, waterfront communities will be impacted by sea level rise of three feet or more. Approximately 16,500 residents in growing neighborhoods such as Bayview-Hunters Point, Mission Bay and Treasure Island would be affected by a four-foot sea level rise scenario – approximately two percent of the county’s current population.
With one-foot local sea level rise, the Bay Area has the largest share of population at risk to inundation exposure. However, sea level rise is experienced at different rates across the country. Although the Bay Area is known to experience sea level rise at a higher rate than the global average, local sea levels along the eastern seaboard and the Gulf of Mexico are predicted to rise approximately twice as fast as on the West Coast. At higher sea level rise forecasts, the East Coast metros of Miami, New York and Philadelphia become increasingly vulnerable. Over one million residents in Miami– nearly one-fifth of the population – live in seaside neighborhoods like Fort Lauderdale and Miami Beach will be at risk for inundation if sea level rises by 4 feet.
Sea level rise focuses on regular inundation, but each metro also has unique flooding risks. In addition to vulnerability to high sea level rise, Miami is at a great risk of flooding due to groundwater emergence. For the Bay Area, as the sea level rises, the risk of flooding increases for creeks and rivers that flow into the Bay.
Metro Comparison for 2015 Population at Risk of Impacts from Sea Level Rise of 1 Foot
San Francisco Bay Conservation and Development Commission/Metropolitan Transportation Commission ART (Adaption to Rising Tides) Bay Area Sea Level Rise Analysis and Mapping Project (2017)
National Oceanic and Atmospheric Administration: Sea Level Rise Maps (2017)
U.S. Census Bureau: Decennial Census
no link available (1990)
U.S. Census Bureau: American Community Survey
5-Year Population Estimates (2011-2015)
Image: Flickr (Creative Commons license), Photographer: Vicki Moore, https://www.flickr.com/photos/vickimoore/2757400175
Projected areas of inundation were developed by BCDC and NOAA at one-foot intervals ranging from one foot to four feet of sea level rise. Regional and local sea level rise analysis is based on data from BCDC’s ART (Adapting to Rising Tides) Bay Area Sea Level Rise and Mapping Project. This data reflects the most up-to-date and detailed sea level rise mapping for the Bay Area. Sea level rise analysis for metro areas is based on national sea level rise mapping from NOAA, which is best for metro-to-metro comparison. To determine the impacts on historical and current populations, inundation areas were overlaid on a U.S. Census shapefile of 2010 Census tracts using Census Bureau population data.
Because census tracts can extend beyond the coastline, the baseline scenario of zero feet was used to determine existing sea level coverage of census tracts. Sea level rise refers to the change from this level. The area of the tract was determined by measuring the component of the tract area not currently under water. This area, rather than the total tract area, was used as the denominator to determine the percentage of the census tract that is inundated under future sea level rise projection scenarios. When at least 10 percent of tract land area is inundated with a given sea level, its residents are considered to be affected by sea level rise.
For the purpose of this analysis, SLR scenarios were assumed not to reflect periodic inundation due to extreme weather events, which may lead to an even greater share of residents affected on a less frequent basis. Prior to the impacts from sea level rise, neighborhoods will experience temporary flooding from extreme weather events which can create significant damage to homes and neighborhoods. It should be noted that by directly reviewing maps and tools through the ART (Adapting to Rising Tides) program, regular inundation sea level rise and temporary flooding from extreme weather events are both available. More information on this approach is available here: http://www.adaptingtorisingtides.org/project/regional-sea-level-rise-map...
Sea level rise analysis for metro areas reflects local, as opposed to global, sea level rise. Recent data has shown sea level is rising faster in the southeast region of the United States. Regional differences in the rate of sea level rise. More information and data related to the rate of sea level rise for different coastal regions is available here: https://oceanservice.noaa.gov/facts/sealevel-global-local.html