Study: Coastal cities at risk as sea rises
Cities along the Gulf Coast are bracing for 10 to 12 inches of sea level rise by 2050, and data from a study in the journal Nature this month showed those risks will be exacerbated as urban areas sink to meet the sea.
Researchers from Virginia Tech, Brown University and other institutions mapped the effects of sea level rise and coastal subsidence, or the sinking of land near the ocean, and found that land sinking would exacerbate sea level rise in some urban areas along the Gulf to a greater degree than other cities in the 32-municipality study.
The study projected that between 2020 and 2050, subsidence would account for about a fifth to a third of the new land below sea level in the urban areas analyzed on the Gulf Coast, compared with just over a tenth on the Atlantic coast and about 5% on the Pacific.
“As sea level rises and land subsides, the hazards associated with climate extremes (for example, hurricanes and storm surges), shoreline erosion and inundation of low-lying coastal areas grow,” the study said.
The authors identified each coastal city’s risk of storm damage using localized data on flooding and calculating how much each segment of land had been subsiding. Sinking ground is found most often in urban areas with claylike soil where groundwater and oil extraction irreparably compact the earth.
“A lot of the coastal areas that we have around the U.S. are made up of young sediment, the latest geological materials to be deposited on land,” said Leonard Ohenhen, a coastal resilience expert at Virginia Tech and the study’s lead author. “They are easily compressible, and that … compaction leads to subsidence.”
His team’s paper looked at the potential costs of high tide flooding for five Texas cities: Port Arthur, Galveston, Texas City, Freeport and Corpus Christi.
The analysis found that across those five coastal cities, thousands more homes and tens of thousands more residents could be exposed by midcentury to flood devastation after the combination of sea level rise and sinking land.
Based on its land features, Port Arthur would see the most residents affected by high tide flooding. The model’s midpoint suggests 23,520 people will be in its path. The costliest home damage would probably occur in Galveston, though, where homes hit by a typical high tide flood would be worth a combined $1 billion. Together, the home value exposure in all 11 Gulf Coast cities analyzed in the study could range from $14 billion to $21 billion in 2050, before factoring in existing flood barriers.
Still, Ohenhen said, the news is not all bad. While his research modeled the hypothetical climate impacts as coastal cities approached the sea, those first calculations did not account for the significant disaster readiness infrastructure already in place or in process along the shoreline.
“All of the consequences are significantly reduced because of that,” Ohenhen said.
Along the Gulf Coast, the model shows current protections such as levee systems should shield a large swath of Texas City and Port Arthur homes, as well as many in New Orleans.
While Galveston is still largely exposed, it might see an additional storm shield if the area’s hotly contested Ike Dike project takes off. The Army Corps of Engineers-led initiative is partially funded and waiting for federal appropriations before breaking ground. The project is likely to take more than a decade to complete once it is funded.