WASHINGTON (June 18, 2018)—Accelerating sea level rise, primarily driven by climate change, is projected to worsen tidal flooding in the U.S., putting as many as 311,000 coastal homes in the lower 48 states with a collective market value of about $117.5 billion in today’s dollars at risk of chronic flooding within the next 30 years—the lifespan of a typical mortgage—according to a new report by the Union of Concerned Scientists (UCS) released today. Roughly 14,000 coastal commercial properties assessed at a value of nearly $18.5 billion also are at risk during that timeframe. By the end of the century, 2.4 million homes and 107,000 commercial properties currently worth more than $1 trillion altogether could be at risk. Despite Pennsylvania not being a purely coastal state, its real estate is still significantly exposed.
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 from high tides—flooding on average 26 times per year or more (or the equivalent of once every other week)—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 projection to use when estimating risk to homes, which are often the owner’s single biggest asset. This scenario projects an average of 1.9 feet of sea level rise in the tidal Delaware River in 2045 and 6.9 feet in 2100. The analysis also projects how many properties might avoid such flooding if sea level rise is constrained through the achievement of the long-term temperature goals of the Paris Agreement and if ice loss is limited.
The results for Pennsylvania, largely around Philadelphia, are sobering. The analysis finds that without additional measures to adapt to rising seas:
- By 2045, more than 400 of today’s residential properties currently home to about 1,000 people, are at risk of chronic inundation. The total number of at-risk residential properties jumps to more than 4,000—home to about 10,000 people—by 2100. The banks of the Delaware River are a patchwork of shoreline stabilization structures, but few of these were designed to keep out higher tides.
- By 2045, more than $115 million-worth of residential property (based on today’s values) is at risk of chronic flooding. The homes that would face this flooding at the end of the century are currently worth more than $1 billion.
- The Pennsylvania homes at risk in 2045 currently contribute about $1.5 million in annual property tax revenue. The homes at risk by 2100 currently contribute more than $14 million collectively in annual property tax revenue.
- Philadelphia and Tinicum are Pennsylvania’s most exposed communities, both in the near and long term. These two communities have about 300 and 90 at-risk properties, respectively, in 2045, and roughly 3,000 and 470 at-risk properties, respectively, in 2100.
- In addition to being the state’s most exposed community, more than one-quarter of Philadelphia’s residents live below the national poverty line and more than 40 percent are African American. Low-income and marginalized households typically have fewer resources available for coping with challenges like flooding.
- By the end of the century, about 300 of today’s commercial properties in Pennsylvania, currently assessed at about $85 million, would experience chronic inundation.
- If nations adhere to the primary goal of the Paris Agreement—capping warming to below 2 degrees Celsius—and there is limited loss of land-based ice, about 86 percent of Pennsylvania’s at-risk homes would avoid chronic flooding by the end of the century, thus safeguarding the vast majority of property values and annual property tax revenue.
Once market risk perceptions catch up with reality, the potential drop in coastal property values could have reverberations throughout the economy—affecting banks, insurers, investors, and developers—potentially triggering regional housing market crises. Homeowners whose properties become chronically inundated may find themselves with mortgages that exceed the value of their homes or face steeply rising flood insurance premiums and may end up defaulting on their loans. Lenders carrying large numbers of these risky mortgages could lose money or even become insolvent, with smaller banks concentrated in areas with high flood risk being especially exposed. Coastal real estate investors and developers may similarly experience financial losses in some coastal areas.
There are currently many federal, state and local policies that, while originally well intentioned, mask risk and create incentives that reinforce the status quo or even expose more people and property to risk. The market’s bias toward short-term decision-making and profits can also perpetuate risky development and investment choices. These flawed policies and incentives include incomplete or outdated flood risk information, subsidized insurance, lax zoning and building codes, incentives for business-as-usual building and re-building, and incomplete credit ratings. Identifying and improving upon the most important policies and market drivers of risky coastal development is a necessary, powerful way to better protect communities and move Pennsylvania and the nation toward greater resilience.
To view the report PDF, click here.
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.