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Rural areas will bear the brunt of US sea-level rise

Rural areas will bear the brunt of US sea level rise

Ghost forests – areas of trees recently killed by rising saltwater – are a clear sign of sea level rise and swamp migration into the countryside. Credit: Dr. Matt Kirwan/VIMS

There is heated debate as to whether coastal wetlands can survive sea level rise by moving inland. A new analysis using highly detailed elevation maps of the Chesapeake Bay region shows that — unlike previous studies — human barriers will do little to slow this swamp migration. Instead, vast areas of low-lying rural land will maintain or even expand the coastal swamps as the saltwater creeps up into what are now forests and farmland.

Lead author Grace Molino, a Ph.D. student at William & Mary’s Virginia Institute of Marine Science, says, “The numbers are striking. Baywide, we expect more than 600 square miles of flooded land in the Chesapeake region by 2100.” That’s four times the area that has turned into wetland in the Bay region since historical sightings began in the 1840s, and more than 75% will be rural — primarily forests, wooded wetlands, and farmland.

Join Molino in the survey, which appears in the latest issue of Limnology and Oceanography Lettershis VIMS professor Dr. Matt Kirwan and US Geological Survey researchers Joel Carr of the Eastern Ecological Science Center and Neil Ganju of the Woods Hole Science Center.

“To my knowledge, this is the first projection of flooded land in the Bay Area, and one of the few highest-resolution forecasts in the US,” Kirwan said. “Our analysis shows that swamp migration is more constrained by natural topography than by human development.”

The authors emphasize that their findings do not only apply to the mid-Atlantic, as similar land use patterns occur along the entire US coast. “Our data suggests that rural coasts will bear the brunt of sea level rise across the country,” Kirwan said.

The team’s study paints the Chesapeake region and the North American coastal plain as global outliers in terms of the salt marsh resilience to sea level rise, with the more urbanized coasts of Europe and Asia more likely to experience ‘coastal squeeze’. This is the loss of coastal wetlands as rising saltwater overflows and erodes their seaward edge, while natural or human barriers block their landward migration.

Kirwan says, “Despite the perception that urban centers will block swamp migration, our predictions suggest that the most vulnerable land in the Chesapeake Bay remains largely undeveloped, even in what is typically considered urban watersheds.”

“We found that developed countries generally cover less than 10% of the predicted migration areas within individual river basins, even in our high sea-level rise scenarios,” adds Molino, “despite more extensive development in the river basin overall.”

For example, the Elizabeth River is one of the most developed watersheds in the Chesapeake Bay and US, with its three branches running through the Norfolk and Portsmouth metropolitan areas of southeastern Virginia. Yet built-up areas cover only 16% of the potential swamp migration area below 1 meter of sea level rise, compared to 31% of built-up land across the entire river basin.

Rural areas will bear the brunt of US sea level rise

The Elizabeth River is one of the most developed watersheds in the Chesapeake Bay and the US; but developed surfaces cover only 16% of the potential swamp migration area below 1 meter of sea level rise. Credit: David Malmquist/VIMS

The Bay’s other major metropolitan areas: Hampton, Virginia; Annapolis, Maryland; and Baltimore, Maryland – are in higher elevations with only small areas of potential swamp migration.

The good news from the study is that the abundance of low-lying forests and farmland in the Chesapeake Bay area and in North America more generally will largely prevent coastal compaction from expanding salt marsh areas in other more urbanized regions of the world’s coast. restrict.

The challenge for North American landowners and governments will be to equitably manage the transformation of what are now largely privately owned, income-generating rural highlands into coastal wetland habitats whose value lies primarily in providing publicly valued ecosystem services such as flood protection and nurturing fish and bird populations.

Analysis

The team began their analysis by using more than 200,000 GIS data points to map the current forest-marsh boundary around the bay. They then recorded the elevation of each point relative to sea level using a highly detailed elevation model from the US Geological Survey. Their next step was to use these data points to calculate a median “threshold height” for each of the 81 watersheds surrounding Chesapeake Bay.

Similar to a bathtub ring, the sill elevation integrates the mix of tidal range and salinity that brought the swamp migration front to its current elevation and lateral position within each watershed segment. These threshold elevations vary by a factor of 5 across the 81 watersheds, from 0.2 to 1.05 meters (0.65 to 3.4 feet). The boundary extends furthest inland in low-lying watersheds bounded by saline waters with a high tidal range. Regular saltwater flooding is the main factor that turns farmlands and forests into salt marsh.

Using the same high-resolution USGS map, the team then added increases in sea level rise to 2100 based on projections from the National Oceanic and Atmospheric Administration, including low (0.5 m or 1.6 feet), average (1 m or 3.3 ft). ) and high (2.5 m or 8.2 ft) scenarios. They then measured the land area within each watershed that would be flooded under any sea level rise scenario and determined whether it is currently covered by forest, wooded wetlands, sod land, agricultural fields or developed surfaces such as roads, parking lots and buildings.

As expected, these “potential swamp migration areas” will increase in the coming decades and with the magnitude of sea level rise, from 405 square miles by 2100 in their low scenario to 1,447 square miles in their high scenario.

What was unexpected in the increasingly developed Chesapeake Bay watershed is that the swamp migration areas are dominated by upland and wetland forests, not urban or suburban land.


North Carolina could lose up to 40% of its wetlands to sea level rise by 2070, new study finds


More information:
Grace D. Molino et al, Variability in swamp migration potential determined by topographic rather than anthropogenic constraints in the Chesapeake Bay region, Limnology and Oceanography Letters (2022). DOI: 10.1002/lol2.10262

Provided by Virginia Institute of Marine Science


Quote: Rural areas will bear the brunt of US sea level rise (2022, June 14), retrieved June 15, 2022 from https://phys.org/news/2022-06-rural-areas-brunt-sea-level.html

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