Sinking land is a ‘hidden vulnerability’ for Hampton Roads, recent study finds

Hampton Roads has a “hidden vulnerability” to the effects of climate change, researchers say.

As scientists continue to study the effects of rising sea levels on coastal communities, they are also warning of the region’s compounded threat of sinking land, or land subsidence.

According to a recent study by Virginia Tech scientists published in the journal Nature Communications, sections of the Chesapeake Bay area are sinking at rates of nearly a quarter of an inch, or about 7 millimeters, per year.

Though not surprising, since Norfolk and surrounding cities have historically been the worst for sea-level rise on the East Coast, cities in Hampton Roads were identified as “hot spots of land subsidence” — occurring at a relatively high rate. This, the study says, exacerbates the effects of sea-level rise and storm surge, since both processes work together to worsen the effects. In the study, researchers used satellite data from 2007-2020 to create high-resolution maps of the East Coast to measure elevation changes.

“There are many estimates and models for sea-level rise, but they all fall short because they don’t take into account land elevation changes,” said Manoochehr Shirzaei, an associate professor of radar remote sensing engineering and environmental security. “When formerly dry land becomes flooded, it causes saltwater contamination of surface and underground water, and it accelerates coastal erosion and wetland losses.”

Some hot spots are sites of “anthropogenic activities,” such as groundwater pumping causing the compaction of aquifer systems, while others are places where land is lost to erosion. Anthropogenic activities are those that originated from human behavior, not natural processes.

“Although we found that most of the bay is sinking by less than 2 millimeters (.079 inches) a year, in several areas, we discovered subsidence rates of 4 to 5 millimeters per year and more,” Sonam Futi Sherpa, lead author of the study said in a statement.

When scientists examined different sea-level rise scenarios compounded with the effect of land subsidence, they found by the year 2100, for the Chesapeake Bay area, 282 to 373 square miles face a risk of flooding. Storm surges similar to Hurricane Isabel’s can increase this, from 527 to 694 square miles from 2030 to 2100. Scientists working on the project said that city planners and leaders should make sure that models they are looking at for flood prevention include sinking land as a factor for flooding. In March, Virginia Tech announced a grant from NASA’s Land-Cover and Land-Use Change Program that will fund a collaborative research project to explore the effects of sea-level rise on coastal communities.

The Virginia Institute of Marine Science at William & Mary released its latest Sea-Level Report Cards. According to VIMS, Norfolk has a rise rate of .212 inches per year, making it the highest rate on the East Coast for a fifth year in a row. The VIMS report card includes land subsidence as a factor, and it estimates the mean sea level in Norfolk will rise 1.5 feet by 2050. Extreme estimates are 2.1-foot rise in sea level on the high end, and just under half a foot on the low extreme.

“Toward the sea, most coastlines are sheltered by coastal wetland ecosystems, providing invaluable physical, chemical, biological, and socioeconomic benefits such as food production, water filtration, preservation of biodiversity, shoreline protection, storm buffering, sediment retention, nutrient cycling, and carbon sequestration,” the introduction to the study reads. “Due to their utility and dynamism, coastal zones are highly vulnerable and sensitive to hazards related to changing environmental and climatic conditions.”

Eliza Noe, eliza.noe@virginiamedia.com