Study: Rising seas weaken nature’s storm shields
When storms like last year’s Hurricane Ida make their way to the continental United States, the first thing they often hit are barrier islands: strips of land parallel to the shoreline, protecting the Atlantic coasts and of the Gulf. Around the world, they can be found protecting around 10% of the planet’s coastline, from Venice Lagoon to Moreton Bay in Brisbane. But a new study suggests they will begin to retreat towards the mainland more quickly as a delayed effect of rising sea levels, diminishing their ability to protect coastlines from storms.
The fate of barrier islands like Dauphin Island in Alabama and Fire Island in New York is important to all coastal residents, even if they don’t live there. Barrier islands protect the mainland from hurricanes, waves, erosion and flooding, taking the first hits of a storm. Without them, experts say hurricane damage to inland towns and villages would be even worse. Last year, Grand Isle in Louisiana, the only inhabited barrier island in the state, faced Hurricane Ida head-on. Nearly half of the houses were demolished and no structure was spared.
“These results can be applied anywhere in the world, but they may be particularly significant in the United States, where homes are built very close to the beach,” said Giulio Mariotti, coastal scientist at Louisiana State University and lead author of the study. , in a press release. Previous studies have estimated that 13 million Americans could be displaced by rising seas and $1 trillion in coastal real estate could be flooded by the end of the century. In May, a viral video of a stilted vacation home on a barrier island in North Carolina’s Outer Banks offered a picture of Americans’ precarious existence on the coast when it collapsed into the ocean.
Scientists created a model based on measurements from a string of islands off the coast of Virginia. Islands are uninhabited, so they are useful for studying a system free of common interventions such as levees or piers. Even though climate change has accelerated sea level rise over the past century, the islands of Virginia have seen little change in the rate at which they migrate, meaning they are eroding and accumulating sand in different places, causing them to change location over time. The model shows that this will not always be the case.
As the seas rose modestly over the past 5,000 years, they created a vast reserve of sand and mud on the coast. Over the past century, storms and tides have devoured these sediments, clearing the way for barrier islands to shift gears. Now that the reserve is depleted, scientists expect rising sea levels to accelerate island movements. Even in the unlikely event that the rate of sea level rise remains the same, scientists predict that the rate at which the Virginia Islands retreat will accelerate by 50% – from 16.5 feet per year to 23 feet. – over the next century. If seas continue to rise, as experts expect, islands would be pushed even closer to shore, leaving coastal communities even more vulnerable.
“This study shows that what we see there today is just a hint of what is to come given increasing rates of sea level rise, and what is likely in store. for developed islands around the world,” said Christopher Hein, co-author of the study. and coastal geologist at the Virginia Institute of Marine Science.
The scientists noted that their prediction could be conservative, as their model does not take into account the strength and frequency of storms, both of which push barrier islands towards the mainland.