Dynamic modeling suggests serious flooding threats much sooner than thought
By Summit Voice
FRISCO — Low-lying islands may be facing more global warming trouble than previously thought.
New modeling that includes storm wind and wave action shows some islands could face regular inundation within the next few decades as sea level rises.
Even if the islands are not permanently submerged, ocean flooding is likely contaminate freshwater supplies, damage agriculture and infrastructure and threaten important bird, sea turtle and marine mammal habitat.
Oceanographer Curt Storlazzi of the USGS Pacific Coastal and Marine Science Center led the study, which compared passive “bathtub” inundation models with dynamic models for two of the Northwestern Hawaiian Islands in the Papahānaumokuākea Marine National Monument.
“Passive ‘bathtub’ inundation models typically used to forecast sea-level rise impacts suggest that most of the low-lying atolls in the Pacific Islands will still be above sea level for the next 50-150 years,” Storlazzi said. “By taking wave-driven processes into account, we forecast that many of the atolls will be inundated, contaminating freshwater supplies and thus making the islands uninhabitable, much sooner,” he said.
The team studied Midway, a classic atoll with islands on the shallow (2–8 meters or 6–26 feet deep) atoll rim and a deep, central lagoon, and Laysan, which is higher, with a 20–30 meter (65–98 feet) deep rim and an island in the center of the atoll. Together, the two locations exhibit landforms and coastal features common to many Pacific islands. Managed by the U.S. Fish and Wildlife Service, they are also among the world’s most important nesting and breeding sites for migratory birds and other wildlife.
The dynamic models suggest that at least twice as much land is forecast to be inundated on Midway and Laysan by sea-level rise than has been projected by passive models.
For example, 91 percent of Midway’s Eastern Island is projected to be inundated under a model that takes into account storm and wave activity accompanied by a sea-level rise of 2 meters (6.5 feet), as compared with only 19 percent under passive sea-level-rise models. Storm waves on Midway are also projected to be three to four times higher than they are today, because more deep-water wave energy could propagate over the atoll rim and larger wind-driven waves could develop on the atoll.
“This report demonstrates the future threat to refuges with the Monument, and the potential impact on nesting seabirds, endangered monk seals and green sea turtles will be considered as we plan for the future,” said Doug Staller, superintendent of the Papahānaumokuākea Marine National Monument.
The findings also have serious implications for tens of thousands of people who live on other low-lying Pacific Island groups such as those found in the Republic of the Marshall Islands and the Federated States of Micronesia.
Because the models attempt to characterize how much land will be washed over by storm waves even if it is not permanently inundated, they offer tools for forecasting where agricultural land may be damaged by repeated saltwater overwash, and where groundwater may be contaminated by saltwater.
The findings suggest that inundation and impacts to infrastructure and terrestrial habitats will occur at lower values of predicted sea-level rise, and thus sooner in the 21st century, than suggested by passive map-based “bathtub” inundation models.