The Impacts of Sea-Level Rise on the California Coast

Over the past century, sea level has risen nearly eight inches along the California coast, and
general circulation model scenarios suggest very substantial increases in sea level as a
significant impact of climate change over the coming century. This study includes a detailed
analysis of the current population, infrastructure, and property at risk from projected sea‐level
rise if no actions are taken to protect the coast. The sea‐level rise scenario was developed by the
State of California from medium to high greenhouse gas emissions scenarios from the
Intergovernmental Panel on Climate Change (IPCC) but does not reflect the worst‐case sea‐level
rise that could occur. We also evaluate the cost of building structural measures to reduce that
risk. If development continues in the areas at risk, all of these estimates will rise. No matter
what policies are implemented in the future, sea‐level rise will inevitably change the character
of the California coast.
We estimate that a 1.4 meter sea‐level rise will put 480,000 people at risk of a 100‐year flood
event, given today’s population. Among those affected are large numbers of low‐income people
and communities of color, which are especially vulnerable. Critical infrastructure, such as roads,
hospitals, schools, emergency facilities, wastewater treatment plants, power plants, and more
will also be at increased risk of inundation, as are vast areas of wetlands and other natural
ecosystems. In addition, the cost of replacing property at risk of coastal flooding under this sea level rise scenario is estimated to be nearly $100 billion (in year 2000 dollars). A number of
structural and non‐structural policies and actions could be implemented to reduce these risks.
For example, we estimate that protecting some vulnerable areas from flooding by building
seawalls and levees will cost at least $14 billion (in year 2000 dollars), with added maintenance
costs of another $1.4 billion per year. Continued development in vulnerable areas will put
additional areas at risk and raise protection costs.
Large sections of the Pacific coast are not vulnerable to flooding, but are highly susceptible to
erosion. We estimate that a 1.4 meter sea‐level rise will accelerate erosion, resulting in a loss of
41 square miles (over 26,000 acres) of California’s coast by 2100. A total of 14,000 people
currently live in the area at risk of future erosion. Additionally, significant transportation related
infrastructure and property are vulnerable to erosion. Statewide flood risk exceeds
erosion risk, but in some counties and localities, coastal erosion poses a greater risk. This report
also provides a comprehensive set of recommendations and strategies for adapting to sea‐level
rise.