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  • USA: More than 386,000 homes at risk of coastal flooding by 2050
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USA: More than 386,000 homes at risk of coastal flooding by 2050

Source(s):  Zillow Group (ZG)

The specter of rising sea levels looms for the more than 40 percent of the U.S. population living in coastal counties. Because sea levels rise slowly and their effects worsen over time, the threat can seem remote. But even now, it’s clear that major financial losses are likely within the next three decades – the lifetime of a typical 30-year mortgage signed in the next couple years.

It is no stretch to say that rising sea levels caused by emissions-driven pollution and warming is one of the greatest threats to homes and their owners that this country has faced. Some are facing acute effects already.

By 2050, more than 386,000 existing homes in U.S. coastal areas are likely to be at risk of permanent inundation from sea level rise alone, or of chronic flooding from a combination of sea level rise and tides and storm surges, if greenhouse gas emissions climb unchecked. The homes are worth $209.6 billion in 2018 dollars – more than four times the estimated insured losses of Hurricane Katrina in 2017 dollars.

Moderate emissions cuts, roughly in line with the Paris agreement on climate, could reduce the number to a little more than 348,000, according to a new analysis and maps that pair Zillow’s housing data with Climate Central’s climate-science expertise. (A companion report focuses on new construction in the riskiest areas.)

Because the effects of climate change worsen over time, estimates for 2100 are even more dramatic: 2.5 million homes worth $1.3 trillion are projected to be at risk by the end of the century if emissions grow unabated. If emissions are cut moderately, 1.3 million current homes worth $714.9 billion sit on land that’s expected to be at risk of inundation from a combination of sea level rise and the type of flooding that currently happens once a year, on average – in other words, a “risk zone.”

Coastal communities will feel the effects of sea level rise to wildly varying degrees, depending on the local rate of sea level rise; local tides and storms; the flatness of the landscape; the number and placement of homes and infrastructure; and the presence of defenses, such as levees. This analysis accounts for existing levees in a national database, but does not account for levees or other defenses that may be added in the future.

The estimated impacts can be surprising. Some major coastal cities, such as Los Angeles, sit high enough above sea level that the worst damage – even as far out as 2100 – may be mostly to their beaches. Other places that have been protected by levees and canals for a century or more, including parts of the San Francisco Bay Area as far inland as Stockton, may be at risk if those defenses fail in a major earthquake or storm. Even when levees hold out bay water, protected areas can face flooding during major rainfall.

Bay Area aside, among the nation’s 150 most-populous cities, Galveston, Texas, and Miami Beach are projected to have the largest share of homes in risk zones by 2050, at 13.1 percent and 10.8 percent, respectively – homes that collectively are worth $3.9 billion. That’s if emissions grow unchecked. By 2100, the city order changes, with Miami Beach projected to have the greatest share of homes in risk zones at 85.2 percent, followed by Miramar, Fla., at 81.5 percent, then Galveston at 78.4 percent.

Even with moderate cuts to greenhouse gas emissions, roughly in line with the Paris agreement, some major U.S. cities are expected to have a large share of homes in risk zones. By 2050, Galveston could be faced with 9.7 percent of its homes in risk zones, followed by Ocean City, Md., (7.3 percent) and Miami Beach (6.6 percent). By 2100, those estimates are: Galveston (46.4 percent), Ocean City (49.1 percent) and Miami Beach (56.8 percent).

With deep cuts – the sort that would have emissions peak in 2020, decline to zero near the year 2070, then see the world pull more carbon dioxide from the atmosphere than it emits – the number of homes forecast to be in risk zones by 2050 nationally is more than 330,000. By 2100, it’s more than 687,000 homes. Under that scenario, Galveston’s projections for 2050 drop slightly from the moderate-cut scenario to 9.5 percent of homes and for 2100 drop considerably to 27.6 percent.

Although the threat posed by rising seas has been widely acknowledged for many years, significant home building has continued in some areas that are projected to be most at risk of inundation. Of the homes built in Miami Beach from 2010 through 2016, for example, 69.2 percent are in areas expected to be at risk by 2100, assuming moderate emissions cuts.

‘Stronger than the storm’

The states with the greatest share of homes in risk zones by 2050, if emissions levels grow unabated, are Louisiana, New Jersey and Delaware, at roughly 2.5 percent each. By 2100, the estimated share in New Jersey will have more than tripled, to 9.2 percent of homes – and development in anticipated risk zones continues. Of the homes built in New Jersey from 2010 through 2017, 16.2 percent are in areas expected to be at risk by 2100 if greenhouse gas emissions grow unchecked.

Rebuilding after Hurricane Sandy, which struck in 2012, accounts for much of the new building in New Jersey.

“After Sandy, the main thrust was to put everything back the way it was as quickly as possible,” said David Kutner, the planning manager for New Jersey Future, a nonprofit that supports sustainable development. “The byword during that period was ‘stronger than the storm,’ which was the height of hubris. There wasn’t consideration for what we were going to be facing down the road.”

New Jersey eventually rolled out a program to buy flood-prone properties at pre-Sandy values, so residents could move elsewhere, but Kutner said the program followed an effort to rebuild and elevate homes. Some homeowners have since told officials that they would rather have been bought out, Kutner said, but the choice they faced at the time was between rebuilding or going without a home.

Government officials in New Jersey and in other coastal states sometimes see disincentives to bringing climate-change issues to the fore, Kutner suggested. “They’re concerned that if they talk about climate risk, it will affect the local tax revenues,” he said.

The logistics and politics of taking action can be tricky for a threat that many people see as distant, despite its imminent dangers. It’s also considered expensive to manage, although the costs of doing nothing may ultimately prove much greater.

Many communities are taking action. Miami Beach is in the midst of a $500 million program to address increased flooding. New York is designing a $203 million flip-up wall to protect parts of lower Manhattan from storm surges.

In Delaware, the state with the lowest mean elevation in the country, seven coastal towns joined together to create the Association of Coastal Towns. One of its biggest questions is whether to adapt to the impacts of climate change – which in such a low-lying state includes many areas not along the seashore – or whether there is a need to retreat instead, said Ted Becker, the mayor of Lewes, Del., and a member of that group.

More immediate considerations include deciding what to do with stormwater runoff and how to handle and pay for the dredging of canals and ditches and the replenishment of beaches and dunes.

Existing adaptation

While 38.6 percent of homes in Charleston, S.C., are projected to be in risk zones by 2100 if pollution grows unchecked – and 20.7 percent with moderate greenhouse gas emissions cuts – the area has long been familiar with what it means to build homes in low country.

“Today it’s a hot topic, but for years, we’ve geared ourselves toward repetitive losses,” said Carl Simmons, the floodplain manager and director of building inspection services for the county of Charleston. “In 10 years, we’ve had a dozen 100-year storms.”

The sea level in Charleston Harbor also has risen a foot in the past century, and NOAA lists it as among the 10 U.S. areas with the greatest increase in nuisance flooding since the mid-twentieth century.

Against that backdrop, Charleston builds – and regulates building – with rising water in mind. Even another two feet from sea level rise would be relatively manageable, Simmons said. If emissions grow unchecked, Charleston could see that much sea level rise by around 2070.

The term “freeboard” is familiar to anyone who works with flooding regulations – and it’s a word the rest of us are likely to hear more as the climate changes and flooding increases.

Freeboard regulations essentially require new buildings to include wiggle room above the flood height expected to occur once in a century – often by building houses on elevated foundations. Freeboard regulations are common among communities that participate in the Federal Emergency Management Agency (FEMA)’s Community Rating System, which offers a break on government flood insurance for homeowners whose communities work to improve the resilience of buildings in local floodplains.

Some places require building above the 500-year floodplain level. Norfolk, Va., goes 18 inches higher than that. And new construction in unincorporated parts of Harris County, Texas, must be two feet above the 500-year floodplain.



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  • Publication date 13 Nov 2018

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