Friday, March 28, 2014

New model now capable of street-level storm-tide predictions

David Malmquist in a press release from the Virginia Institute of Marine Science at William & Mary:   The water that surged into the intersection of New York City’s Canal and Hudson streets during Hurricane Sandy—to choose just one flood-ravaged locale—was ultimately driven ashore by forces swirling hundreds of miles out in the Atlantic.

That simple fact shows not only the scale and power of a tropical cyclone, but the difficulty of modeling and forecasting its potential for coastal flooding on the fine scale needed to most effectively prepare a response.

Sandy caused more than $50 billion in damage, left millions without electricity, and killed 72 people. © Sandy caused more than $50 billion in damage, left millions without electricity, and killed 72 people. © Now, a study led by Professor Harry Wang of William & Mary’s Virginia Institute of Marine Science demonstrates the ability to predict a hurricane’s storm tide at the level of individual neighborhoods and streets—a much finer scale than current operational methods.

The study, published in today’s issue of the Journal of Marine Science and Engineering, shows that with the right input, the team’s high-resolution computer model was able to simulate water levels to within 6-8 inches of those observed in New York City and surrounding areas during Hurricane Sandy’s approach and landfall in late October 2012. This includes sections of Manhattan where buildings and other infrastructure divert and channel floodwaters in exceptionally co
mplex ways.

“Storm-surge modeling is a tough problem,” says Wang. “People are interested in the possibility of flooding on a very fine scale, on the order of their house, office, or street.” But for a forecast model to work, he says, “We have to resolve the boundary conditions——data on tides and winds—very far away, out into the open ocean. And we have to have that information far enough beforehand to provide time for people and agencies to respond.”

Wang and his modeling team—fellow VIMS researchers Derek Loftis, Zhuo Liu, David Forrest, and Joseph Zhang—conducted their study by “hindcasting” Hurricane Sandy’s landfall along the U.S. Atlantic coast. In this technique, scientists initiate a computer model with data collected before a past event, and then test the model’s accuracy by comparing its output with observations recorded as the event unfolded....

Modeling Animation: Storm-tide flooding of the Battery in New York City through several tidal cycles during Hurricane Sandy as modeled by Professor Harry Wang and colleagues at VIMS. Values are in meters above sea level. Still from animation created by Dr. David Forrest.

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