“What If NYC” to solicit designs for large-scale post-disaster housing. Above, one of the entrants’ visions.” width=”600″ height=”400″>

Photo by: NYC

In 2008 the New York City Office of Emergency Management administered a competition called “What If NYC” to solicit designs for large-scale post-disaster housing. Above, one of the entrants’ visions.

The city of New York announced the first mandatory evacuation in its history this afternoon, with Mayor Bloomberg warning in a City Hall press conference: “This is very serious. Do not be fooled by the sun outside. It literally is the calm before the storm.”

The evacuation order applies to all residents in the city’s lowest-lying and most vulnerable coastal areas—those designated Zone A on the city’s hurricane evacuation map, basically encompassing Coney Island and Manhattan Beach in Brooklyn, Broad Channel and the Rockaways in Queens, South Beach and Midland Beach in Staten Island, Battery Park City and small areas of City Island, Throggs Neck, Hunts Point and Highbridge in the Bronx. The city at 4 p.m. today is opening 91 emergency shelters for evacuees—who are supposed to be out of their neighborhoods by 5 p.m.

The mass transit system will begin shutting down at noon, making things tough for evacuees who wait until the last minute.

Beyond the Zone A areas, the rest of the Rockaways—some of which lie in Zone B—are also under a mandatory evacuation order because the city worries that bridges linking the peninsula to the mainland will be shut by high winds, hampering emergency response in the area.

With the storm still hundreds of miles away, Bloomberg acknowledged that Hurricane Irene could still pass substantially west or east of the city, but added: “There is no question that we are going to get hit by some wind and high water that is very dangerous … It’s heading basically directly for us.”

As City Limits reported in 2008, New York City has long lived with a high risk for dangerous hurricanes—their rare occurrence being offset by the destructive potential that such storms can have on the metro area because of the shape of our part of the Atlantic coastline:

New York City’s Office of Emergency Management says that in a Category 3 or 4 hurricane, up to 2.3 million city residents would need to evacuate and some 600,000 would require temporary shelter. In other words, a population the size of Houston would need to leave home and a subset as big as Boston would need a place to stay.

Storms of that intensity have been unlikely in New York because nearby ocean waters are relatively cool, but climate change could increase the risks as waters warm and sea levels rise. By 2100, the city might see today’s “100-year storm” every decade or two.

Without cold water to protect it, New York City is very vulnerable to a major storm. The city has 600 miles of coastline and lies at a point where the Atlantic Coast makes a nearly 90-degree bend that could amplify a storm surge. Major bridges are so high that winds might force their closure, obstructing evacuation. Columbia University’s Center for Climate Systems Research reports that flooding during storms in 1960 and 1992 came within a foot or two of causing “massive inundation and even loss of life” in the subway system.

The Army Corps of Engineers has said that if 1985’s Hurricane Gloria (which veered east) struck closer to the city and at high tide, the impact would have been devastating.