In summary

For low-income Americans, the number of homes at risk of flooding could triple by 2050, researchers say. Three Bay Area cities are among the top at-risk communities.

California’s crisis of affordable housing appears to be running smack into another intractable problem: sea level rise

A new study published this week projects that the number of affordable housing units at risk of flooding in the United States is projected to more than triple by 2050.

“In terms of the absolute number of units exposed….threats are primarily clustered in smaller cities in California and in the northeastern United States,” the study found. 

Three Bay Area cities are included in the top 20 at-risk cities in the United States identified by the researchers: Corte Madera in Marin County, Foster City in San Mateo County and Suisun City in Solano County. 

Affordable housing has a greater chance of flooding than general housing “in nearly all of the top-ranked cities,” according to the researchers.

Marlin Cove, an apartment complex with affordable housing units, sits at the edge of the water in Foster City. Photo by Anne Wernikoff for CalMatters

In California, the number of affordable housing units in danger of flooding is expected to increase 40% by 2050, the analysis found. 

Scientists say floods have worsened in recent decades along the nation’s coasts, and they project that rising seas triggered by climate change will increase the frequency of routine tidal flooding as well as extreme floods.

Conducted by environmental scientists and the non-profit research group Climate Central, the findings shine a light on a harsh truth about climate change: The impacts fall most often on the less fortunate.

“Climate impacts are not evenly distributed,” said Lara Cushing a UCLA environmental health scientist and one of the report’s authors. “We know that low income communities and communities of color are more vulnerable.

“Affordable housing units may be physically more vulnerable to climate impacts if they are built to older housing codes, and less structurally sound,” she said.

“And the people living in affordable units—the disabled, single parents, seniors, people of color—have fewer resources to cope with flooding impacts, they tend to have less political influence on where government invests resources on flood mitigation and are less likely to be insured.”

Foster’s Landing apartments, a housing complex that includes low income units, was built across the street from a water access point in Foster City. Photo by Anne Wernikoff for CalMatters

The analysis used a new Microsoft mapping tool that outlined the footprint of every building in the continental United States. That allowed for a more granular view of where buildings are located and, using sea level rise projections and levee data, how much flooding risk they face. The researchers added an overlay of demographic data to determine who resided in the at-risk buildings. 

Sea level rise and flooding is a menace in many of  the state’s coastal regions, but only the three Northern California towns made the top 20 list of vulnerable US cities. That’s because of their low elevation and clusters of affordable housing, the authors said.

“In the Bay Area, we built the cheaper housing and low-income housing on the Bay side, and the rich people live in the hills,” said Evelyn Stivers, executive director of the Housing Leadership Council of San Mateo County, which advocates for affordable housing.

“The people living in affordable units—the disabled, single parents, seniors, people of color— tend to have less political influence on where government invests resources on flood mitigation.”

lara cushing, environmental health scientist at ucla

Foster City — with the San Francisco Bay at its front door and the Pacific Ocean at its back — was identified as having a remarkable degree of vulnerability: More than 90% of its affordable housing is at risk of flooding or direct impacts from rising seas.

However, the report noted that its analysis did not take into account the city’s upcoming flood control measures. Foster City voters in 2018 approved a $90 million bond for levee improvements, parts of which are under construction.

When that project is completed, “the level of exposure of the affordable units will be significantly much less than the previous estimate of 90%,” said Monica Ly, a Foster City assistant planner.

In addition, the city has an ordinance that requires all new private housing developments to set aside 20% of their units for low-income residents. Ly said that Foster City is one of only about two dozen towns in California to have met its affordable housing targets.

Rachel Morello-Frosch, a UC Berkeley environmental health scientist and study co-author, said the analysis can be a critical tool for local policymakers and planners.

“What this paper does is make sure that when we are talking about threats to people who live in affordable housing, we consider sea level rise,” Morello-Frosch said. “If we are going to preserve affordable housing stock in coastal areas, that’s going to require significant investment.”

The researchers used projections that take into account various scenarios about whether planet-warming greenhouse gases will continue to be emitted globally at their current pace.

In nearly all the top-ranked cities, the report found that the percentage of the affordable housing stock at risk of flooding exceeded that of the general housing stock. Corte Madera and Suisun City were among the communities with the widest disparities between which type of housing faced the greatest risk.

Panel A shows the total expected annual exposure of affordable housing units and the number of units expected to be exposed at least four times per year. Panel B shows expected annual exposures as percentages of total affordable and general housing stocks. Cities are ordered geographically following coastlines from east to west. Study published on Environmental Research Letters

New Jersey was identified as “the most vulnerable state,” facing a four-fold increase in flooding between 2000 and 2050. New York City, Atlantic City and Boston had the highest absolute number of residential units at risk. But, in the case of New York City, only 1% of its low-income housing was vulnerable to flooding.

Pennsylvania, Florida and South Carolina face the biggest projected growth between 2000 and 2050 in the percentage exposed to flooding, with increases of 792%, 774% and 669%, respectively.

“Nationwide, affordable housing is an increasingly scarce resource,” the study says. “Nationwide, there are only an estimated 35 affordable rental units available for every 100 extremely low-income renters… — a national shortfall of over 7 million units that impacts all 50 largest metropolitan areas. ”

Housing advocates said California can begin to shape a housing policy that addresses future risk if they pay attention to the science of sea level rise.

“It is absolutely not a surprise that low-income people have all these conditions that come together where they are the first and hardest to be hit by crisis,”  said Amie Fishman, executive director of the Non-Profit Housing Association of Northern California.

 “We need comprehensive solutions to housing that take into account sea level rise. The solution is to make sure we are investing in quality and sustainable affordable housing. That is what we are doing in California, but there’s not enough.”

Future threat of coastal flooding to states, based on projected sea levels for the year 2050. Study published on Environmental Research Letters

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Julie Cart joined CalMatters as a projects and environment reporter in 2016 after a long career at the Los Angeles Times, where she held many positions: sportswriter, national correspondent and environment...