New research indicates that isolation from essential services like food and safe drinking water due to flooded roadways may be a bigger problem than property flooding for residents of coastal states 

TAMPA FL, December 5, 2022 – The record-breaking storm surge that swept away people and homes along Florida’s southwest coast during Hurricane Ian was amplified by sea level rise, a measurable impact of rising temperatures. Since 1993, the global sea level has risen 10 cm (almost four inches), due to the expansion of warmer ocean water and the melting of glaciers and ice sheets. By 2050, it is expected to rise another 25 to 30 cm (10 to 12 inches) along the U.S. coastline. This means that deadly and destructive storm surges will push farther inland than they once did, and more people will be impacted by flooding.   

Civil systems engineer Dr. Tom Logan of the University of Canterbury will present new research on how and where Americans will be affected most by rising sea level at the Society for Risk Analysis Annual Meeting, Dec. 4-8 in Tampa, Florida. In a nationwide study of U.S. coastal counties, he and colleagues, including Dr. Allison Reilly from the University of Maryland College Park, compared the number of people at risk from inundation (property flooding) to the number of people at risk of isolation (being cut off from essential infrastructure and services) based on different predicted scenarios of sea-level rise over the next 100 years.  

Their analysis revealed that the number of Americans at risk from sea-level rise can be more than double in some states when the impacts of population isolation due to flooding are taken into account. The researchers define “risk of isolation” as the potential for a localized lack of physical connectivity by roadway to public accommodations. Flooded roadways mean that residents are unable to reach supermarkets, work, education, and healthcare facilities, or be reached by emergency services. Residents who lose electricity, internet, and potable and waste water services may also be unable to safely remain in their homes, even if their home remains dry.  

When the impacts of population isolation are taken into account, the study showed that some coastal states are at much greater risk than others. The percentage of residents at risk of isolation is significantly higher for residents of Maryland, Delaware, Rhode Island, and Oregon. The percentage of residents at risk of inundation is highest for Florida.  

The typical displacement metric for sea-level rise adaptation planning is “parcel inundation” (property flooding). Logan and his colleagues argue that their study shows this does not capture the wider cascading or indirect effects of sea-level rise. Their results indicate that nearly 4 million residents are at risk of isolation, but never at risk of inundation. “This means that current planning efforts based on inundation risk may ignore or overlook these communities when distributing resources or other support,” says Logan.   

In their analysis, the researchers assessed whether people are cut off or isolated from services when roadways are inundated during mean higher high-water tides in the coastal U.S. for different sea-level rise scenarios. To estimate the extent of sea-level rise, the team used the future sea-level rise scenario maps developed by NOAA. For sea-level rise projections, they added in relative sea level change for different climate scenarios from a recent study. (These levels range from 0.3 m to 2.0m by 2100.)  

“We found impacts in regions that would otherwise not expect to be at risk from sea level rise — for example, in Maine — and also discovered those impacts could happen decades earlier than expected,” says Logan. “This means that inundation-based forecasts of risk are underestimating when the impacts will occur, and this difference can be considerable.” 

The researchers have created an interactive web dashboard that enables viewers to compare the risk of inundation and risk of isolation and explore where and when these risks may occur under different NOAA sea-level rise scenarios:    

“This study improves our estimate of the risk, who is at risk, and when those risks start to become intolerable,” says Logan. “It also helps officials prioritize support for at-risk communities. As nations develop their climate adaptation strategies, our research shows they must consider more than just direct flood risk.” 

Logan will present his study, “Isolation” Revising the Estimated Risk of Sea-Level Rise” on ______ as part of a symposium on  Adaptation Planning of Engineered Systems for Climate Change.