Residential properties in the contiguous U.S. at risk of coastal flooding from sea level rise in 2045 and 2100. Graphic: Union of Concerned Scientists

(UCS) – Sea levels are rising. Tides are inching higher. High-tide floods are becoming more frequent and reaching farther inland. And hundreds of US coastal communities will soon face chronic, disruptive flooding that directly affects people's homes, lives, and properties.

Yet property values in most coastal real estate markets do not currently reflect this risk. And most homeowners, communities, and investors are not aware of the financial losses they may soon face.

This analysis [Underwater: Rising Seas, Chronic Floods, and the Implications for US Coastal Real Estate (2018)] looks at what's at risk for US coastal real estate from sea level rise—and the challenges and choices we face now and in the decades to come.

A threshold of disruption

Long before rising seas permanently submerge properties, millions of Americans living in coastal communities will face more frequent and disruptive high-tide flooding. As this flooding increases, it will reach a threshold where normal routines become impossible and coastal residents, communities, and businesses are forced to make difficult, often costly choices.

For this analysis, that threshold is defined as flooding that occurs 26 times per year (on average, once every other week) or more, a level of disruption referred to as chronic inundation. It is important to note that this flooding is not caused by storms—it is simply the result of high tides rising higher, and reaching farther inland, as sea levels rise.

The results identify the number of residential and commercial properties at risk of chronic inundation—and the total current property value, estimated population, and property tax base affected—for the entire coastline of the lower 48 states.

Billions of dollars of property at risk

The analysis finds that:

  • More than 300,000 of today's coastal homes, with a collective market value of about $117.5 billion today, are at risk of chronic inundation in 2045—a timeframe that falls within the lifespan of a 30-year mortgage issued today. Approximately 14,000 coastal commercial properties, currently assessed at a value of roughly $18.5 billion, are also at risk during that timeframe.
  • By the end of the century, homes and commercial properties currently worth more than $1 trillion could be at risk. This includes as many as 2.4 million homes—the rough equivalent of all the homes in Los Angeles and Houston combined—that are collectively valued today at approximately $912 billion.    
  • The properties at risk by 2045 currently house 550,000 people and contribute nearly $1.5 billion toward today's property tax base. Those numbers jump to about 4.7 million people and $12 billion by 2100.  
  • States with the most homes at risk by the end of the century are Florida, with about 1 million homes (more than 10% of the state's current residential properties); New Jersey, with 250,000 homes; and New York with 143,000 homes. 

These results reflect a 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. Even with a more moderate (intermediate) rate of sea level rise, nearly 140,000 homes are still at risk of chronic inundation by 2035 and more than 1.2 million by 2100. (See below for more information about the sea level rise scenarios used in this analysis.)

It is also important to note that these results do not include future development or new homes, nor do they include critical infrastructure such as roads, bridges, power plants, airports, ports, public buildings, and military bases. When all of these are taken together, the effects of chronic flooding could have staggering economic impacts.

The growing risks to homeowners, communities, and the economy

The challenges and choices that come with rising seas are profound and have significant implications for coastal residents, communities, and the broader economy.

Homeowners and commercial property owners are at risk of steep financial losses if their properties flood regularly. Declining property values could erode the tax base for communities, jeopardizing funding for vital local services and infrastructure, such as roads, schools, and police and fire departments.

Mortgages on homes that could become chronically flooded during the term of the loan are inherently riskier. As flooding becomes more frequent, the value of flooded homes will decline and many homeowners could find themselves with mortgages that exceed the value of their homes, or with homes that are increasingly difficult to insure or have even deteriorated to the point of being unlivable. With no obvious option for reversing that trend, some might choose to abandon their homes and allow banks to foreclose on their mortgages. Banks holding these risky mortgages on devalued properties could then find their financial position adversely affected. 

Mortgage-backed securities and bonds tied into these riskier coastal real estate mortgages will be at risk of losing value. Real estate developers and investors as well are at risk of losing money invested in properties that become chronically flooded.

Once market risk perceptions catch up with reality, the potential drop in coastal property values could have broad reverberations—affecting banks, insurers, investors, developers, and taxpayers—and potentially trigger regional housing market crises as well as affect the broader national economy.

A national imperative for action

Given the enormity of the risks from sea level rise, communities, states, businesses, and the federal government all need to take action to prepare.

A crucial first step is for communities, policymakers, and the financial sector to know the risks and amount of time they have available for a robust response.

The nation must also implement policies that reduce the carbon emissions that cause global warming, including investments in clean energy solutions; re-orient policy and market incentives to better reflect the risks of sea level rise and build coastal resilience while also ensuring that resources are targeted to low-income and otherwise disadvantaged communities; and adopt bold, transformative policies that foster new frontiers of opportunity on safer ground for those who may have to retreat from high-risk areas.

The risks of rising seas are profound. Many of the challenges they bring are inevitable. And our time to act is running out. There is no simple solution—but we do still have opportunities to limit the harms. Whether we react to this threat by implementing science-based, coordinated, and equitable solu­tions—or walk, eyes open, toward a crisis—is up to us right now.

About this analysis

To determine the number of coastal properties at risk from this level of chronic flooding, the analysis uses property data from the online real estate company Zillow combined with the findings of the 2017 analysis, When Rising Seas Hit Home: Hard Choices Ahead for Hundreds of US Coastal Communities, which uses a peer-reviewed methodology to assess areas at risk of chronic inundation.

Three sea level rise scenarios, developed by the National Oceanic and Atmospheric Administration (NOAA) and localized for this analysis, are included:

  • A high scenario that assumes a continued rise in global carbon emissions and an increasing loss of land ice; global average sea level is projected to rise about 2 feet by 2045 and about 6.5 feet by 2100.
  • An intermediate scenario that assumes global carbon emissions rise through the middle of the century then begin to decline, and ice sheets melt at rates in line with historical observations; global average sea level is projected to rise about 1 foot by 2035 and about 4 feet by 2100.
  • A low scenario that assumes nations successfully limit global warming to less than 2 degrees Celsius (the goal set by the Paris Climate Agreement) and ice loss is limited; global average sea level is projected to rise about 1.6 feet by 2100.

For more information on the sources and methodology used for this analysis, please see the full report and technical backgrounder. [more]

Underwater: Rising Seas, Chronic Floods, and the Implications for US Coastal Real Estate (2018)


By Giuliana Viglione
25 June 2018

(King5 News) – Rising seas will threaten more than 7,000 Washington homes by 2045, according to a new report by the Union of Concerned Scientists (UCS). Accelerating melt from the Antarctic ice sheet is predicted to cause more frequent and more powerful storms to hammer coastal communities, amounting to potentially billions of dollars of damage over the next several decades.

More than 23,000 residential properties are at risk of chronic inundation by 2100. Thirteen percent of these homes are in King County, accounting for nearly a quarter of the property value the UCS says is at risk in Washington.

The UCS defines chronic inundation as flooding at least 26 times per year. This number represents a tipping point for communities — the point at which they would be forced to act, explains Kristina Dahl, a senior climate scientist with the UCS.

“First and foremost, we feel that communities need to understand the risks that they face and the time frame in which they face them,” says Dahl. “Some communities have just 15-20 years before this becomes a really serious issue.”

The last resort is to pack up and move to higher elevations — already a reality for members of the Quileute Tribe and the Quinault Indian Nation, both located on the western shores of Washington. Both groups are seeking funds to move key buildings to higher elevation.

The UCS report uses 6.3 feet of sea level rise by 2100 to make their predictions. While this is on the higher end of climate scientists’ projections, it is within the realm of possibility, says Ian Miller, a coastal hazard specialist with the Washington Sea Grant. And these predictions are looking more and more likely based on new research out of Antarctica.

A recent survey of Antarctic ice sheet research combined data from 24 estimates of ice loss dating back to 1991. Scientists found that melt from the icy continent has added about 0.3 inches of sea level rise globally over that period — and the rate is accelerating. […]

Washington residents can expect destructive storms to occur more frequently over the coming decades. As sea levels continue to rise, waves and swells will be able to store more energy. Storms that were projected to happen once in a century may occur every decade.

“The difference between the 100-year storm and the ten or two-year storm is pretty minor,” says Guillaume Mauger, a research scientist at the University of Washington’s Climate Impacts Group. “It doesn’t take a lot of sea level rise to tip the scales.”

Mauger doesn’t hold out much hope for avoiding the oncoming storms. “Our projection suggests that by 2100, there’s a 98–100 percent chance that we get [6 inches] sea level rise. It’s virtually guaranteed.” [more]

Storms of the century may be on the rise in King County

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