![]() ![]() ![]() ![]() Surge strength and local geography can change the likelihood and location of compound flooding. Areas at particular risk from compound flooding are those near some of the major river watersheds, including the Tar-Pamlico and Neuse basins, both of which empty into Pamlico Sound, says Jessica Whitehead, a hazards adaptation strategist with the North Carolina Sea Grant. Forecasts indicate up to 30 inches of rain, with some isolated spots possibly reaching 40 inches. As Florence lingers, it will continue to push surge ashore and rains will pile up. The entire Southeast coast is a hotspot for this type of flooding, in part because it is prone to being hit by tropical systems, according to a 2015 study spearheaded by Thomas Wahl, a civil engineer at the University of Central Florida.Ī similar situation could play out with Florence, which is expected to stall once it makes landfall, sandwiched in by two atmospheric high-pressure systems, as happened with Harvey. “That’s just a completely different impact than we’ve traditionally prepared for,” says Antonia Sebastian, an associate research scientist at Texas A&M University at Galveston, who studied the event. As a result, people can be trapped with no direction to escape, possibly without power or food-as they were during Harvey, necessitating widespread search and rescue operations. Water rises everywhere and can stay that way for days. That high water can stop heavy rain from draining. But if a huge storm stalls along the coast, high seas can continue to push onto land after the initial surge. Typically, a storm surge pushes in, then washes out heavy rain falls on the coast and inland, draining via gravity to the sea, often via rivers and streams. Although that storm’s record rains would have caused terrible flooding on their own, the moderate ocean surge that lingered in Galveston Bay as Harvey stalled meant floodwaters stayed high for days. Compound flooding contributed to the unprecedented inundation of the Houston area during Hurricane Harvey. But compound flooding arises when both dynamics meet, exacerbating the overall impact. Meanwhile torrential rains can overwhelm the ground and rivers, causing floods even hundreds of miles inland. “We have ignored it in the past, we cannot ignore it in the future,” says Amir AghaKouchak, a civil engineer at the University of California, Irvine, who has studied the issue.Īs a tropical storm reaches land, its winds pile up ocean water in front of it, pushing a surge ashore. Now it is gaining attention among researchers and coastal emergency managers working to better understand who and what will be flooded during extreme weather events as well as how threats might change as coastal populations boom and the climate transforms. But the combination of the two-a situation called compound flooding-could make floodwaters even higher, last longer and reach farther inland than anticipated.Ĭompound flooding is complex, so it has generally not been considered in flood forecasting and prevention planning. Hurricane Florence is bearing down on the U.S as a major hurricane that could inundate the coast with up to 13 feet of surging ocean water and more than two feet of rain.Įach of those flood hazards can do devastating damage on their own. ![]()
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