Sea-Level Rise Could Leave Many Marooned Earlier, UMD Study Finds

For U.S. coastal dwellers grappling with rising sea levels, the decision of whether to fight the tide or flee for drier land may come sooner than previously predicted, according to new University of Maryland research.

Published this month in Nature Climate Change, the study goes beyond previous work examining seawater inundation of properties to find that isolation—when seawater engulfs roads, preventing access to essential services like hospitals, shopping and education—can take place decades earlier. An online dashboard created alongside the paper graphically represents rising waters as they cause both conditions around the country.

“Metrics that are based on inundation can really overestimate the amount of time that we actually have to respond to the changing climate,” said civil and environmental engineering Assistant Professor Allison Reilly, one of the study’s authors. “We need to factor in isolation as well.”

The study examined all coastal counties within the United States, combining the OpenStreetMap road network with scenarios for sea-level rise from the National Oceanographic and Atmospheric Administration. Using variables such as mobility behavior (where people access shopping, work and education), road elevation and travel routes, the authors were able to quantify the likelihood—and to project a timeline—for when specific areas would be cut off from essential services.

They found that the risk of isolation not only impacts areas previously considered low-risk, but will likely result in earlier displacement of communities. Isolation during higher high-water tides is between 30-90% higher than property inundation, and is several times higher in some states.

While previous studies have focused mainly on inundation of properties as a benchmark for evacuation or retreat, Reilly, who co-wrote the paper with lead author T.M. Logan and M.J. Anderson, both of the University of Canterbury, New Zealand, said that viewpoint overlooks factors such as how sea-level rise can obstruct drainage systems, deteriorate roadways and damage other infrastructure.

“Right now, these communities aren’t experiencing those problems, but that will change in 10 to 15 years,” she said.

The dashboard, which allows users to dial different amounts of sea-level rise, offers a striking visualization of the impact for coastal communities; for example, one foot in Maryland would likely isolate around 5,000 people on Kent Island, Md. without significant infrastructure modification. The dashboard and study, said Reilly, can supply policymakers and local officials with easily accessible, actionable information that can be used to manage access issues, whether by elevating roadways or armoring them against saltwater damage, or by decommissioning them as the communities they serve migrate elsewhere.

“Many state agencies just don’t have the data they need to understand what their isolation risks are, and we’d like to start that conversation,” Reilly said. “We hope our research will encourage state departments of transportation to think about how to best manage road assets, given these risks.”