A new study of sea level rise using detailed data on land elevation changes found that current scientific models may not accurately capture vulnerabilities in 32 coastal cities in the United States.
The reviewpublished Wednesday in Nature, uses satellite imagery to detect land subsidence and uplift to help paint a more accurate picture of exposure to flooding both now and in the future.
Nearly 40 percent of Americans live on coasts, where subsidence, or land subsidence, can add significantly to the threat of sea level rise. While the Gulf Coast is experiencing many of the worst cases of subsidence — parts of Galveston, Texas, and Grand Isle, La., are falling into the ocean faster than the global average sea level is rising — the trend is visible throughout the United States coast.
Many widely used sea level projections account for subsidence by looking at long-term trends derived from data collected by tide gauges, even though the sites may be miles away from population centers. . “Usually they only represent measurements at one location of how the ground is moving,” and not the overall spatial dynamics of the entire city, said Leonard Ohenhen, a Ph.D. candidate at Virginia Tech and the paper’s lead author.
The work by Mr. Ohenhen, Manoochehr Shirzai, Chandrakanta Ojha and colleagues shows how coastal land is sinking into the ocean, exacerbating the risk from global sea-level rise. The new study extends their analysis of elevation changes along the Atlantic Coast to the Gulf and West, and uses these maps to explore potential flooding within major coastal cities in more detail.
“This will increase accuracy on the time scale of decades, because it offers higher spatial resolution,” said Bob Kopp, a climate scientist at Rutgers University, who helped review the new paper for Nature .
The research assumes, however, that the trends observed in the relatively short satellite record, from 2007 to 2020, can be extrapolated at a constant rate into the future. This can happen in areas that are sinking due to natural causes. But human activities, such as the extraction of groundwater or oil and gas are a major factor in subsidence in many areas.
“Groundwater withdrawal is a major reason why Atlantic City is sinking faster than New York City,” said Dr. Kopp. “Can you assume they continue at their current rate for 30 years? Maybe. Can you assume they can for 100 years? I probably wouldn’t.”
