Higher Tides Will Threaten More than 20,000 California Homes by Mid-Century

Sea Level Rise Puts $187 Million in Property Tax Revenue in Jeopardy

Published Jun 18, 2018

OAKLAND, Calif. (June 18, 2018)—Accelerating sea level rise along California’s shoreline, primarily driven by climate change, is projected to put more than 20,000 coastal homes at risk of chronic, disruptive flooding within the next 30 years, according to a report released today by the Union of Concerned Scientists (UCS). The California homes at risk have an assessed value of more than $15 billion in today’s dollars, though market value is considerably more.

The analysis combines property data from the online real estate company Zillow with a peer-reviewed methodology developed by UCS for assessing areas at risk of frequent flooding. Using three sea level rise scenarios developed by the National Oceanic and Atmospheric Administration and localized for this analysis, UCS determined how many residential and commercial properties along the entire lower 48 coastline are at risk of becoming chronically inundated, flooding on average 26 times per year or more, in the coming decades even in the absence of major storms. The core results in the report are from the high sea level rise scenario—an appropriately conservative approach to estimating risk to homes, which are often the owner’s single biggest asset.

“We’ve known for years that many California communities and beaches will face sea level rise impacts by the end of the century, but now we know the actual number of homes that could be affected in the near term,” said Dr. Kristina Dahl, senior climate scientist at UCS and co-author of the report. “When you consider that 30 years is the span of a typical mortgage, the implications of these numbers are startling. Frequent flooding from higher tides will significantly reduce the livability of many neighborhoods and could drive home values down.”

Along the lower 48 coastline, 2.4 million homes and 107,000 commercial properties, collectively worth more than $1 trillion today, are at risk by 2100, according to the report. While California can expect more than 100,000 homes to be at risk by the end of the century, Florida faces a harrowing future with about 1 million homes, or about 10 percent of the state’s current residential properties, at risk by 2100.

As property values decrease, the municipal property tax base that funds schools, roads, emergency services, and climate adaptation measures in affected communities will also shrink, according to the report. The 20,000 California homes at risk in 2045 contribute nearly $187 million in annual property taxes today; that revenue source, and the services it funds, would be increasingly in jeopardy. By 2100, these numbers jump to nearly 110,000 at-risk homes that today contribute nearly $1 billion in property taxes annually. Municipalities may be looking at even deeper revenue declines when commercial property, sales and other business tax losses are factored in.

The California counties with the most homes at risk of chronic inundation are Marin, San Mateo and Orange. Marin County can expect nearly 4,400 homes, representing roughly $40 million in annual property tax revenue today to be at risk of chronic inundation due to sea level rise by 2045, and over 10,000 homes and $95 million in annual tax revenue to be at risk by 2100. San Mateo County can expect 4,100 homes and about $30 million in property tax revenue to be at risk by 2045, and more than 32,000 homes and about $245 million in property tax revenue to be at risk by 2100. Orange County can expect roughly 3,700 homes and about $44 million in property tax revenue to be at risk by 2045, and about 12,300 homes and $153 million in property tax revenue to be at risk by 2100.

Marin and San Mateo counties are among eight California jurisdictions suing fossil fuel companies for damages caused by climate change. The cities of Imperial Beach, Oakland, Richmond, San Francisco and Santa Cruz, and Santa Cruz County have also filed civil lawsuits. Combined, the eight jurisdictions can expect rising seas to put at risk about 8,800 homes that pay $76 million annually in property taxes by 2045, and roughly 52,000 homes with a collective $435 million annual property tax bill by 2100.

“Climate change compounds so many of our state’s existing problems,” said Adrienne Alvord, Western States director at UCS. “Less coastal land will be available for housing in the coming decades while at the same time, existing housing in coastal communities will be feeling the squeeze of chronic flooding. That’s bad news for a state grappling with a housing crisis and a growing population. It means local coffers could be strained precisely at a time when cities and counties may be wrestling with a choice between expensive, temporary protective measures or expensive relocations.”

Meanwhile, the loss of coastal property values will have reverberations throughout the economy—affecting banks, insurers, investors, and developers—potentially triggering regional housing market crises or a more widespread economic crisis. Homeowners whose properties become chronically inundated could find themselves with mortgages that exceed the value of their homes, face steeply rising flood insurance premiums, or even default on their loans. Lenders carrying large numbers of these risky mortgages could lose money or eventually become insolvent. Coastal real estate investors and developers may similarly experience financial losses in some coastal areas.  

“There are currently many well-intentioned federal, state and local policies that mask risk and create incentives that reinforce the status quo or even expose more people and property to risk,” said Rachel Cleetus, an economist and policy director for the Climate and Energy Program at UCS, as well as a report co-author. “The market’s bias toward short-term decision-making and profits can also perpetuate risky investment choices.”

The UCS study analyzed three sea level rise scenarios. In the lowest scenario, which assumes the goals of the Paris Agreement are met and ice loss is limited, 80 percent of the homes at risk in California—nearly 90,000 in total, accounting for more than $750 million in property tax revenue—could be spared this century.

“We have a rapidly narrowing window of time in which to reduce our carbon emissions to try to constrain future sea level rise,” said Dahl. “By striving for a future with less sea level rise, we’re giving communities across the country the best possible chance to maintain their characters and their livelihoods. For a city like Alameda, the difference between 1.3 feet and 6.3 feet of sea level rise is that only 400 homes would be at risk of chronic flooding at the end of the century versus nearly 9,000 homes. For each family not flooded out, that’s a profound difference.”

To view the report PDF, click here.

Spreadsheets with data about the chronically inundated properties are available and can be sorted by state, by community (delineated by the Census Bureau as county subdivisions), and by ZIP code.

To use the interactive mapping tool, click here. The map allows you to learn more about the impact of chronic inundation on properties, people, home values and the tax base in specific states, communities or ZIP codes. When you zoom in, the maps become more detailed. You can also click on a specific state or community for more details about it.

For all other materials, including our methodology document, a compilation of interviews with additional experts on this topic, and Spanish-language materials, click here

Data provided by third parties through the Zillow Transaction and Assessment Dataset (ZTRAX). More information on accessing the data can be found at http://www.zillow.com/ztrax.

The results and opinions presented in this report are those of the Union of Concerned Scientists and do not reflect the position of Zillow Group. See full disclaimer at www.ucsusa.org/underwater.