San Mateo County: Cascading Effects of Sea Level Rise Could Affect Everyone

Sea Change San Mateo County Office of Sustainability California State Coastal Conservancy StateAECOM Arcadis Circlepoint U.S. Geological Survey

By Jacob Bourne

In April, San Mateo County’s Office of Sustainability released the draft report, Sea Level Rise Vulnerability Assessment. The report is part of a broader initiative called Sea Change San Mateo County that’s working towards analyzing sea level rise risks and creating a responsive action plan to meet the forecasted challenges. The 291-page report was compiled with funding from the California State Coastal Conservancy and relied on consulting services from AECOM, Arcadis and Circlepoint, as well as assistance from a plethora of private and public sector entities. The initiative was spurred by the finding that sea level rise is a primary impact of global climate change and that San Mateo County is deemed highly vulnerable to this impact in terms of public safety, infrastructure, natural resources and the local economy.

Sea Change San Mateo County Office of Sustainability California State Coastal Conservancy StateAECOM Arcadis Circlepoint U.S. Geological Survey

“This draft report is the culmination of significant work on the part of our Office of Sustainability staff who used the best modeling tools available to identify areas where sea level rise should be considered in future planning and building,” said Supervisor Dave Pine, who has led the County’s efforts to develop the vulnerability assessment and prepare for sea level rise. “San Mateo County is one of the most vulnerable areas in the U.S. to sea level rise with thousands of lives and billions of dollars of property at risk. This document represents a major step forward in addressing this risk.”

The overarching goals of the report are to assess the level of vulnerability, identify the consequences of not taking action, take necessary actions informed by research, promote community awareness and work collaboratively. The report’s findings are based on data from the U.S. Geological Survey, Point Blue’s Our Coast, Our Future and the Pacific Institute Study.

Put in economic terms, the value of the County’s land parcels poised to be affected by near-term flooding associated with sea level rise amounts to $1 billion, while long-term flooding is expected to impact parcels totaling $39.1 billion. According to the National Climate Assessment, “The future costs of inaction are estimated to be 4 to 10 times higher than the current costs of investing in climate change adaptation and hazard mitigation measures.”

The report is largely based on research indicating that California experienced seven inches of sea level rise between 1905 and 2005, with a rate of increase that’s projected to accelerate in coming decades fueling coastal storm surges and inland flooding. Although climate modeling includes a range of uncertainty, it’s estimated that the state could experience up to one foot of sea level rise by 2030, two feet by 2050 and 5.5 feet by 2100. The exact amount of sea level rise does vary by location, however some climate scientists assert that these estimates are conservative.

In San Mateo County one of the many potential effects of sea level rise is saltwater intrusion into aquifers and groundwater sources causing damage and contamination. The report provides a snapshot of possible outcomes given various scenarios and highlights especially vulnerable areas such as Bair Island State Park and East Palo Alto, which could experience significant flooding from one foot of sea level rise. In the event of two feet of sea level rise, “SFO becomes inundated” and three feet will heavily impact Peninsula transportation infrastructure including Highway 101. The authors note that if SFO were inundated it’s also highly likely that San Carlos and Oakland airports would be under water as well. Such impacts could reverberate globally.

Those who live or work on higher ground would also be impacted in these scenarios due to “cascading impacts” in which the geographic impact of flooding reaches further than merely the flooded area. For example, if flood waters were to contaminate a fuel oil tank and the water seeped into the power generator, then power would be lost for higher ground and low lying areas alike.

Health impacts of sea level rise range from loss of access to medical services, exposure to toxic waste and the spread of infectious disease. The report states, “San Mateo County has 29 sites classified as hazardous materials or clean-up sites that are expected to be exposed to flooding in the near-term, and up to 665 sites that are expected to be exposed to flooding in the long-term.”

The next step for the County is to put together a working group and steering committee to create an action plan to address the findings of the assessment. At the municipal level, planning efforts to identify funding for adaptation projects will be necessary. Some of the ways to bolster the resiliency of the built environment are to utilize elevation and flood-proofing strategies and develop floating structures such as bridges. Authors stressed that flexibility in adaptation management is crucial so that measures like seawalls are built with foundations that can be raised if needed.

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