Thousands of Coastal Residents at Increased Risk of Sinking Land by 2050

Research -- A recent study offers a thorough examination of the likelihood of flooding in a total of 32 communities located along the Atlantic, Pacific, and Gulf coasts.

The analysis forecasts that up to 500,000 individuals would experience the consequences of floods in the next 30 years, with approximately 1 in 35 privately held properties being affected. Additionally, it emphasizes the ethnic and socioeconomic characteristics of the individuals who may be impacted.

Research done by Virginia Tech indicates that by 2050, around 2% of the population residing in twenty-four coastal communities in the United States may encounter substantial flooding.

The study, published in the scientific journal Nature, integrates satellite-derived data on land subsidence, sea-level rise forecasts, and tide charts to offer a comprehensive assessment of flood risk in 32 communities located along the Atlantic, Pacific, and Gulf coasts. According to the report, it is estimated that up to 500,000 individuals might be impacted and around 1 in 35 privately owned properties could experience flood damage during the next thirty years. The study also emphasizes the ethnic and socioeconomic characteristics of those who may be impacted.

"One of the challenges we have with communicating the issue of sea-level rise and land subsidence broadly is it often seems like a long-term problem, like something whose impacts will only manifest at the end of the century, which many people may not care about," said lead author Leonard Ohenhen, a graduate student working with Associate Professor Manoochehr Shirzaei at Virginia Tech's Earth Observation and Innovation Lab. "What we've done here is focused the picture on the short term, just 26 years from now."

Other increases compared to current estimates include:

Between 500 and 700 more square miles of land flooded
176,000 to 518,000 more people affected
94,000 to 288,000 more properties exposed with an estimated value of $32 billion to $109 billion

The project involved collaboration with Chandrakanta Ojha from the India Institute of Science Education and Research in Punjab, India.

Sonam Sherpa is a former Ph.D. student at Virginia Tech and a postdoctoral fellow at Brown University.
Robert J. Nicholls is affiliated with the Tyndall Centre for Climate Change Research at the University of East Anglia in the United Kingdom.

"This study demonstrates that we can now measure vertical land motion at a sufficient scale to create a useful climate service that supports planning and management decisions on flooding," said Nicholls, a professor of climate adaptation. "This approach has the potential to be applied in any city around the world, really supporting adaptation."

Using highly accurate data points measured by space-based radar satellites, Shirzaei and his research team have built some of the world's first high-resolution depictions of the sinking land along the coast of the entire United States. Their work has previously revealed regions of the Atlantic coast to be sinking by as much as 5 millimeters per year.

 This study revealed that 24 of the 32 coastal cities are currently sinking more than 2 millimeters per year and half of those cities have areas sinking more than global seas are rising. These numbers might seem small, but when combined with sea-level rise over time, it adds up to quite a significant shift, according to Ohenhen.

"The analogy I have found that is really helpful in helping people understand this change is to think about a sinking boat," he said. "Imagine you are in that boat with a steady leak, slowly causing the boat to sink. That leak symbolizes sea-level rise or broadly flooding. What would happen if it also starts raining? Even a minor rainfall or drizzle would cause the boat to sink more quickly than you thought it would. That's what land subsidence does -- even imperceptible millimeter land subsidence exacerbates existing coastal hazards."

Along with the new flood projections, the study also revealed the 32 cities have a combined 131 flood control structures, such as levees, berms, or dikes, but that 50 percent of those are located on the California coast. Only three of the 11 Atlantic coast cities studied maintain levees or floodwalls.

"When we looked at it across the board, we found that there is a general unappreciation for flood protection, particularly on the Atlantic coast," Ohenhen said. "And even the levees there often protect less than 10 percent of the city, compared to other cities on the Pacific or Gulf coasts where up to 70 percent is protected."

Another first in the study is the consideration of racial and socioeconomic demographics related to the potentially affected areas.

In some cities examined, particularly those along the Gulf Coast, the potential increased exposure fell disproportionately on racial minorities. In other cities, the properties facing increased exposure were found to generally be of lesser value than the median property value of the area. And in a few cities, New Orleans and Port Arthur, Texas, particularly, these two demographics intersect, showing the areas with greatest potential risk to be disproportionately occupied by people of color who are also at an economic disadvantage when compared to the city as a whole.