Over 13 million US homes flooded by 2100 due to sea level rise

Over 13 million US homes in 219 coastal counties face serious flooding by 2100 following sea level rises caused by climate change, say scientists from the University of Georgia, who believe their study could help protect those properties if policymakers take targeted action.

The researchers explained in the prestigious journal Nature Climate Change (citation below) that theirs is the first study to assess the risk from rising oceans using year 2100 population forecasts for all 319 coastal counties in the US mainland.

Previous studies on the impact of climate change and sea level rises used current population figures.

Flood risk USA sea level risesCumulative projected at-risk populations for the continental United States, 2010–2100. Projections reflect assumed growth/decline rates for 72,664 census block groups in 319 coastal counties. (Image: nature.com)

This latest study is based on data that was gathered and analyzed as part of Mathew Hauer’s doctoral work with the UGA Franklin College of Art and Sciences; Jason Evans, a former UGA faculty member who is currently at Stetson University; and Deepak Mishra, Associate Professor at the UGA Department of Geography.

6-foot sea level rise

If the sea level rises by six feet by the end of this century, based on 2100 population forecasts, over 13 million homes will be exposed to flooding and other hazards linked to rising waters.

In Florida alone, the most severely-affected state, up to six million residents are likely to be affected, plus one million in Louisiana and one million in California.

In this study, the researchers estimated that sea levels could rise by three to six feet by the end of the century. Even at the lower end (just 3 feet), population trends suggest that over 4.2 million coastal residents on the US mainland would be at serious risk, Hauer said.

Current and future populations at risk of floodingProjected cumulative populations at risk of sea-level rise by 2100 under the 1.8 m scenario. The study considered 22 states and the District of Columbia. (Image: nature.com)

Current estimates downplay potential impact

According to Hauer:

“The impact projections are up to three times larger than current estimates, which significantly underestimate the effect of sea level rise in the United States. In fact, there are 31 counties where more than 100,000 residents could be affected by 6 feet of sea level rise.”

The authors believe their data could help policymakers determine where to focus practical adaptation strategies for protecting land and properties threatened by frequent and repeated flooding, said Mishra.

Mishra commented:

“This research merges population forecasts with sea level rise. It gives policymakers more detailed information to help them assess how sea level rise will affect people and infrastructure.”

By employing population projections for the year 2100, the data also provide a more accurate and relevant measure of the potential flooding risks in some of the USA’s fastest-growing communities, the authors wrote.

For example, over one-quarter of all residents in major urban centers like New Orleans and Miami could face coastal flooding by the year 2100 if adaptive measures are not taken.

The authors(Left) Jason Evans, (Middle) Deepak Mishra, and Mathew Hauer.

Regarding the urgency of adaptation measures, Hauer said:

“Adaptation strategies are costly, and these are areas of especially rapid population growth, so the longer we wait to implement adaptation measures the more expensive they become.”

Eighty percent of residents living in Monroe County (Florida Kays), Hyde and Tyrrel (two lightly populated countries on the North Carolina coast), would be impacted if sea levels rise by 6 feet by the end of this century.

A six-foot rise would affect over 10% of people living in Georgia’s coastal counties with regular and severe flooding, plus 18% of those living in Chatham County (Savannah) and 29% in Glynn County (Brunswick).

People in other parts of the country would also be affected by a 6-foot sea level rise. Over 16% of residents in San Mateo County in California, just south of San Francisco, and more than 10% of those living in Nassau County, New York, would suffer.

In an Abstract in the journal, the authors wrote:

“These results suggest that the absence of protective measures could lead to US population movements of a magnitude similar to the twentieth century Great Migration of southern African-Americans.”

“Furthermore, our population projection approach can be readily adapted to assess other hazards or to model future per capita economic impacts.”

Citation: Millions projected to be at risk from sea-level rise in the continental United States,” Mathew E. Hauer, Jason M. Evans & Deepak R. Mishra. Nature Climate Change. 14 March, 2016. DOI: 10.1038/nclimate2961.

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