Report Says 2.5 Million Homes, Businesses Totaling $1 Trillion Threatened by High Tide Flooding

The Union of Concerned Scientists said climate change is putting coastal communities at huge risk–to the tune of more than $1 trillion.

A new UCS report said accelerating sea level rise in the lower 48 states, primarily driven by climate change, is projected to worsen tidal flooding, putting as many as 311,000 coastal homes with a collective market value of nearly $120 billion today at risk of chronic flooding within the next 30 years–the lifespan of a typical mortgage.

The report said nearly 14,000 coastal commercial properties assessed at a value of nearly $18 billion are also at risk during that timeframe. By the end of the century, homes and businesses currently worth more than $1 trillion could be at risk, representing as many as 2.4 million homes–the equivalent of all the homes in Los Angeles and Houston combined–valued at $912 billion and 107,000 commercial properties assessed at $152 billion.

“What’s striking as we look along our coasts is that the significant risks of sea level rise to properties identified in our study often aren’t reflected in current home values in coastal real estate markets,” said Rachel Cleetus, an economist and policy director for the Climate and Energy Program at UCS and report co-author. “Unfortunately, in the years ahead many coastal communities will face declining property values as risk perceptions catch up with reality. In contrast with previous housing market crashes, values of properties chronically inundated due to sea level rise are unlikely to recover and will only continue to go further underwater, literally and figuratively.”

The analysis uses property data from Zillow Inc., Seattle, combined 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, 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 an average of 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–a conservative projection to use when estimating risk to homes, which are often the owner’s single biggest asset.

The report said the consequences of chronic flooding of properties in specific communities could translate not just into eroding property values, but also into unlivable houses and falling tax revenues that fund schools, roads and emergency services in those places. UCS estimated properties at risk by 2045 currently house 550,000 people and contribute nearly $1.5 billion toward today’s property tax base. These numbers jump to 4.7 million people and $12 billion by 2100.

“For some communities, the potential hit to the local tax base could be staggering,” said Kristy Dahl, senior climate scientist with UCS and report co-author. “Some smaller, more rural communities may see 30, 50, or even 70 percent of their property tax revenue at risk due to the number of chronically inundated homes. Tax base erosion could create particular challenges for communities already struggling with high poverty rates.”

The report said states with the most homes at risk by the end of the century are Florida, with one million homes or more than 10 percent of the state’s current residential properties; New Jersey with 250,000 homes; and New York with 143,000 homes. States that could lose the most in home property values by 2100 are Florida at $351 billion, New Jersey at $108 billion, and New York at nearly $100 billion.

Decreases in property values also mean a lower property tax base. Florida, New York and New Jersey will see the biggest hits to their annual property tax revenue with municipalities losing about $5 billion, $1.9 billion and $1.7 billion total, respectively.

However, the report noted widespread economic consequences across the coasts. Nearly 175 communities would expect to see 10 percent or more of their homes at risk of chronic flooding by 2045, with nearly 60 of those communities experiencing poverty levels above the national average. Additionally, of 75 communities with 30 percent or more of their property tax base at risk, t one-third of these have poverty rates above the national average. The places that could be hit hardest in this way include communities in: Louisiana, Maryland, New Jerse, and North Carolina. Similarly, communities with large African American or Hispanic populations–many located in California, Florida, Louisiana, New Jersey, New York, South Carolina and Texas–could also be at an inherent disadvantage in taking steps to prevent or recover from chronic flooding, due to longstanding social and economic inequities.

More specifically, the report said loss of coastal property values could 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,” the report said. “Lenders carrying large numbers of these risky mortgages could lose money or eventually become insolvent, with smaller banks concentrated in regions with high flood risk being especially exposed. Coastal real estate investors and developers may similarly experience financial losses in some coastal areas.”

“Actions today, especially the amount of global warming emissions we release, will help determine what our coasts will look like at the end of the century,” said Astrid Caldas, senior climate scientist at UCS and report co-author. “If we manage to meet the goals of the Paris Agreement by keeping warming to between 1.5 and 2 degrees Celsius and if ice loss is limited, 85 percent of all affected residential properties-valued at $782 billion today and currently accounting for more than $10.4 billion in annual property tax revenue to municipal governments-could avoid chronic flooding this century. The longer we wait to drastically reduce emissions, the less likely it is that we will achieve this outcome.”

“Targeting improvements to the policies and market drivers of risky coastal development is essential to better protect communities and move the nation toward greater resilience,” said Shana Udvardy, climate resilience analyst at UCS and report co-author. “Short-sighted policies and market drivers will need to be phased-out to discourage risky behavior and to ensure changes won’t be too jarring on homeowners and the real estate market.”

The report can be found at