Rising seas and affordable housing

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.

In California, the number of affordable housing units in danger of flooding is expected to increase 40 percent 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.”

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.

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 percent of its affordable housing is at risk of flooding or direct impacts from rising seas.

However, the repor t 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 percent,” 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 lowincome 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,” MorelloFrosch 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 planetwarming greenhouse gases will continue to be emitted globally at their current pace.

In nearly all the topranked 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.