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Florence, Mangkhut bring data and destruction to coastal scientists

Hurricane Florence dawdled over North Carolina, dropping catastrophic amounts of rain.

Reuters/Jonathan Drake

By Frankie Schembri

Weather and marine scientists were awestruck last week as they watched deadly, record-breaking storms evolve on opposite sides of the globe. Now, they are scrambling to analyze a torrent of data on the origins and impacts of the storms, collected by satellites, gauges, robotic submarines, and other instruments. They are also assessing damage to research infrastructure.

In Asia, Typhoon Mangkhut made landfall early on 15 September local time on northern Luzon in the Philippines, killing at least 70 people, many in massive mudslides. It went on to pound Hong Kong, China, with some of the strongest winds and highest storm tides recorded there in the modern era.

At about the same time in North America, Hurricane Florence came ashore near Wilmington, North Carolina. Its winds were far weaker, but it produced unprecedented rainfall and flooding, killing at least 34 people and leaving several coastal science facilities in tatters. 

At the Duke University Marine Lab in Beaufort, North Carolina, the “terrifying” hurricane “peeled [the roof] off our primary teaching building” and left many dormitories “uninhabitable,” says Director Andrew Read. Florence also severely damaged Dobo Hall, a main science building at the University of North Carolina in Wilmington. It’s not clear how long it will take to reopen the campuses, officials say.

Off Wilmington’s coast, 8-meter waves and chaotic currents dragged a buoy equipped with sensors that measure wind speeds, wave heights, and other conditions more than a kilometer from its mooring. But as of early this week, it was still transmitting data, says Debra Hernandez, executive director of the buoy’s operator, the Southeast Coastal Ocean Observing Regional Association in Charleston, South Carolina. She was waiting to find out whether an instrument that tracks ocean currents with high-frequency radar, silent since the storm, is still intact. It could take years to replace lost instruments, she notes, because her network relies mostly on federal funding that must work its way through Congress.

In China, ocean researchers at The University of Hong Kong (HKU) dodged a bullet when 175-kilometer-per-hour winds and high waves slammed into The Swire Institute of Marine Science, which is perched on an exposed peninsula. The facility “took a lot of damage,” says Director Gray Williams, an intertidal ecologist. “But it hasn’t affected us at all,” because the institute’s specimens, experiments, and major equipment were out of harm’s way. They had been moved to the main HKU campus several months ago to allow for a major renovation and expansion. “The timing was fortuitous,” Williams says.

Other researchers are beginning to comb through data on the storms themselves. In the Pacific Ocean, monitoring networks confirmed that Typhoon Mangkhut was the most powerful seen this year, with winds peaking at 287 kilometers per hour. But the Philippines got a bit lucky, says I-I Lin, a specialist in typhoon-ocean interactions at National Taiwan University in Taipei: The storm passed over relatively cool surface waters before it made landfall, sapping some of its power.

In the United States, however, researchers say a warming climate likely contributed to Florence’s extraordinary rainfall, which totaled more than a meter in some areas and fed floodwaters that overtopped measuring gauges put in place to document the storm’s impact. Warm air simply holds more water, researchers note. On top of that, there’s evidence that warming is slowing the forward motion of storms, potentially by weakening the temperature differentials that drive steering winds, allowing the rain to linger.

That slowing, described in Nature earlier this year by a group led by climate scientist James Kossin of the University of Wisconsin in Madison, was certainly a factor in the flooding that Hurricane Harvey caused last year in Texas. “Now we have another textbook example with Florence,” Kossin says. “The main thing that Florence is doing is that it’s not moving.” At one point, the storm was creeping along at some 3 kilometers per hour, he notes. “I’m old and I can walk faster than that.”

Florence also underscored the importance of winds in driving coastal flooding, says computer scientist Russell Clark of Georgia Institute of Technology in Atlanta. People tend to focus on a hurricane’s maximum wind speeds, he says, but that can be “very misleading. It is the sustained onshore winds over multiple days, over a large area, that have caused the waters to pile up in the bays and rivers, leaving nowhere for this massive rainfall to go.” Those winds partly explain why New Bern, North Carolina, a small town hard hit by floodwaters, “started flooding … even before the worst of the rain had arrived.”

More insight into the behavior of Florence—and future storms—could come from two automated submarine gliders and other sensors deployed along the continental shelf in the hurricane’s path. The sensors “have given us a really cool view of what’s happening on the shelf,” including how subsurface temperatures and salinities changed as Florence churned, says Catherine Edwards, a marine researcher at the University of Georgia’s Skidaway Institute of Oceanography in Savannah. She predicts the data will useful in improving forecasts.

The pattern of blown-out windows in Hong Kong’s tall building canyons may offer lessons for cities, says Deng Xiaowei, an HKU structural engineer. When wind is channeled between buildings set close together, it can accelerate and become turbulent, shattering windows. Current building codes don’t “consider sufficiently the interaction of buildings in the local wind environment,” Deng says.

Landslides in the Philippines highlight another shortcoming of current disaster prevention efforts. “Extreme rainfall was forecast, landslide hazard maps showing nearby safe areas were available, and yet we have many deaths,” says Alfredo Mahar Francisco Lagmay, a geologist at the University of the Philippines Diliman in Quezon City. In one heartbreaking incident 200 kilometers north of Manila, dozens of miners and their families took shelter in a makeshift chapel that was buried when the slope above it collapsed. The site had been designated as dangerous, and safer locations were just several hundred meters away. But hazard maps for the region, though available online, had never been printed and distributed. 

With reporting by Dennis Normile and Paul Voosen.

Source: Science Mag

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