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sea level rise risks on San Mateo County coast
sea level rise

Sea Level Rise

As the climate changes and sea levels rise, communities in the Bay Area are already experiencing the impacts of flooding. The magnitude and extent of sea level rise-linked flooding and erosion are expected to increase in the future. Learn more about storm-linked flooding.

Understanding how sea level rise is likely to affect San Mateo County residents, businesses, and the community services and infrastructure we all rely on is crucial to building prepared, healthy, and safe communities. 

The San Mateo County Flood and Sea Level Rise Resiliency District (“OneShoreline”) began operating in 2020 to coordinate countywide efforts to combat the harms of sea level rise caused by climate change. OneShoreline provides expertise in the complex process of designing and building for sea level rise, working with cities and developers to build resilience through planning and coordinating multi-jurisdictional flood mitigation projects. Learn more about OneShoreline.


Places at Risk

In addition to the flooding risk to many of our communities, our networked infrastructure is also at risk. Sea level rise is expected to affect us all through impacts to roads and highways, electric substations, and wastewater treatment plants that are essential to day-to-day community and economic functions. For example, a flooded highway, wastewater treatment plant or electrical substation could temporarily shut-down businesses, close roads and lead to many community-wide disruptions. By working together, we can protect our communities’ many assets, including neighborhoods, businesses, parks and beaches – places we all love.

South Coast Sea Level Rise Risk and Solutions Study

Study area: from the southern edge of Half Moon Bay to the county line south of Pescadero

The San Mateo County South Coast is known for its iconic beaches, agricultural areas, and small coastal communities. Many of these areas, including Coastside beaches and bluffs, roads, agricultural land, businesses and residences are already at risk from flooding and erosion, and these impacts will get worse as sea level continues to rise. Our communities need to know what to expect and what we need to start doing today to protect ourselves from these impacts. The South Coast Sea Level Rise Vulnerability Assessment can help us do just that.

This study evaluates the impacts of sea level rise on the South Coast right now, at .8 feet, at 1.4 feet and at 4.9 feet. The vulnerability assessment provides projections of the extent of coastal hazards and of the physical and economic impacts to community assets like buildings, roads, farmland, and coastal access infrastructure. Learn more in the Executive Summary (PDF) and the full report (PDF).

To make the information in this report more accessible, we developed interactive maps in English and Spanish to guide the public through the study findings. Click below to learn more.

San Mateo County Sea Level Rise Vulnerability Assessment

Study area: the San Mateo County Coast and bay shorelines except for the South Coast

Understanding how sea level rise will affect San Mateo County residents, businesses, and the community services and infrastructure we all rely on is a crucial step in building prepared, healthy and safe communities.  Sea level rise could affect communities, community services and critical facilities, energy networks, transportation systems, flood protection infrastructure, natural and recreational areas, wastewater and stormwater systems, and closed landfills and solid waste facilities. Learn more in the San Mateo County Sea Level Rise Vulnerability Assessment (PDF) full report or view the Highlights Brochure (PDF) and the Asset Vulnerability Profiles (PDF).

Possible Adaptation Strategies

There are many strategies available to address the challenges of sea level rise. San Mateo County Sea Level Rise Vulnerability Assessments have identified three key categories of adaptation strategies: (1) emergency preparedness and resilience efforts, (2) shoreline and site-specific strategies, and (3) policies, plans and procedure updates to address sea level rise. 

Countywide Strategies

  • Adopt new development standards and ordinances for at risk areas.
  • Utilize nature-based solutions, including vegetated, permeable, and tree-covered surfaces, water detention systems and habitat restoration.
  • Update building design standards and codes to incorporate flood risk best practices.

South Coast Strategies

  • Implement protection approaches that attempt to stop erosion or flooding.
  • Plan for accommodation approaches that allow for erosion and flooding while minimizing damages.
  • Consider managed retreat or hazard avoidance, which relocates or realigns potentially vulnerable infrastructure.

Communities that invest in adaptation understand that the alternative—inaction—will likely result in costly damage, cleanup, and emergency repairs.

Sea Level Rise Policy and Implementation Plan for County-Owned Assets

In 2019, the Board of Supervisors approved a Sea Level Rise Policy for County-Owned Assets. The Policy requires that sea level rise is considered in all County-owned and operated assets, design and construction projects, leases, and property acquisitions and dispositions.

These projects must also consider local and regional sea level rise adaptation and flood mitigation projects that could reduce impacts on County-owned assets prior to developing plans to modify existing facilities.

The intent of this policy is to understand the vulnerability of County-owned property and assets over their life cycle; develop an incremental approach to adaptation based on the current and future level of risk; and coordinate with other communities on developing regional solutions.

Implementation of this policy is expected to increase the useful life of County facilities; protect residents and staff today and assure County operations will be continuous; reduce the current and future risks from sea level rise and flooding; reduce liability; and reduce insurance premiums and impacts to property value.

Based on this policy, all new facility projects funded by the County shall be sited, designed, constructed, and adaptively managed to minimize sea level rise risks over the life of the project. Following a baseline assessment of sea level rise vulnerability, existing facilities and properties will be subject to this policy during the Capital Improvement Planning or acquisition process, if major renovations or replacement of existing facilities and infrastructure are located in areas at risk from sea level rise beyond what will be protected through local or regional planned sea level rise adaptation projects.

Learn more through the 2019 San Mateo County Sea Level Rise Policy for County-Owned Assets (PDF) and Implementation Plan (PDF).

2019 SeaChange SMC Community Resilience Grants

The SeaChange SMC Community Resilience Grants Program supported cities and organizations in developing solutions that reduce impacts from sea level rise. Learn more.

2018-2019 Nature-Based Shoreline Protection Strategies Project

Nature-based strategies protect shorelines from coastal flooding by creating, restoring, or emulating natural coastal features, such as wetlands, dunes, or reefs. These strategies reduce erosion and mitigate storm surge, wave action, and still-water flooding associated with coastal flood events.

SeaChange SMC worked with Stanford’s Natural Capital Project (NatCap) and the San Francisco Estuary Institute (SFEI) to explore and evaluate a menu of nature-based sea level rise strategies for the County’s Bay shoreline. The project identified “Operational Landscape Units” OLUs with shared geophysical and habitat characteristics suited for particular sets of adaptation strategies. These natural “neighborhoods” cross jurisdictional and traditional decision-making boundaries making coordination essential to achieve successful adaptation.

Five factsheets summarize the San Mateo County bayside risks from sea level rise, nature-based opportunities to reduce these risks, and the potential ecosystem services that could be achieved through OLU-focused nature-based strategies. Learn more:

This project was funded by The Gordon and Betty Moore Foundation.