On the edge of retreat
"An island community moved to the mainland. Now the fast-rising sea is following — a warning for the rest of the East Coast.
Monthly data for all contiguous U.S. tide gauges from the National Oceanic and Atmospheric Administration’s Sea Level Trends page were analyzed over 1993-2021, with 1993 chosen to match the first full year of the satellite sea level record. Linear trends were calculated using an approach that takes into account autocorrelated errors, following the methodology that NOAA has outlined for analyzing sea level trends.
For each site, we required that at least 70 percent of years have complete data (i.e., 12 monthly values); this affected 19 sites out of 103 in the contiguous United States. All trends have an associated uncertainty; for Virginia, this ranges from +/- 1.15 millimeters per year at Kiptopeke, Va., to +/- 1.47 mm per year at the Chesapeake Bay Bridge-Tunnel, where data are unavailable after 2017.
Different methods exist for calculating sea level trends. We also examined 1993-2021 trends calculated by the University of Hawaii Sea Level Center for a select group of U.S. tide gauges, and trends calculated over a slightly different period (1990-2020) by the Permanent Service for Mean Sea Level. In most cases, the results are similar, especially for the U.S. East Coast.
There is no long-term tide gauge record at Oyster, Va., and it is not clear which existing Virginia gauge would most closely reflect the changes there. The nearest record, at Kiptopeke, shows seas rising by 4.7 millimeters per year, somewhat lower than other Virginia records. This could reflect lower rates of land sinking or some other factor related to the placement of the gauge, according to Molly Mitchell at the Virginia Institute of Marine Science. (Subsidence rates are not expected to change greatly going forward, and this would not affect future trends related to climate change.)
Hampton Roads is about 30 miles from Oyster and is generally a benchmark for the region. The trend there is also the midpoint among the five Virginia sites in our analysis, with two sites showing lower rates and two showing higher ones.
Sinking land is a factor in many U.S. tide gauge readings, not just in Virginia. U.S. sea level rise rates are highest on the Gulf Coast, where land subsidence rates also tend to be the highest because of oil and gas and drinking water extraction, and other factors. However, satellite trends suggest that sea level rise offshore is also elevated along the Gulf Coast, just as it is along the southeastern U.S. coast.
Global gridded sea level data is from the NOAA Laboratory for Satellite Altimetry; the mapped data show trends from late 1992 through early 2022, as calculated by NOAA.
The 1959 aerial photo of Hog Island is from the U.S. Geological Survey’s Earth Resources Observation and Science (EROS) Center; Hog Island’s 2022 satellite imagery is from Planet Labs PBC; historical maps of Hog Island are from NOAA’s Historical Map & Chart Collection. Calculations of area changes to the Virginia barrier islands are from Robbins et al, Geomorphology, 2022.
John Muyskens contributed to this report.
Photos courtesy of the Eastern Shore of Virginia Barrier Islands Center Inc., Donna Fauber, Lisha Bell and the Division of Work and Industry, National Museum of American History, Smithsonian Institution.
Design and development by Hailey Haymond and Jake Crump. Editing by Monica Ulmanu, Katie Zezima, Joe Moore, and Angela Hill. Copy editing by Mike Cirelli."
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