New York City's business and government leaders may have been surprised by the sheer size of Hurricane Sandy and the wall of water that flooded major parts of the city. But that storm's successor won't find a city so unprepared, executives said Thursday at the Rebuilding NY conference hosted by Crain's New York Business.

Some proposals offered at the event were far more aggressive than government initiatives currently underway. Gov. Andrew Cuomo has already rolled out the first phase of his $400 million voluntary buyout program in badly damaged neighborhoods of Staten Island, but a prominent geologist from that borough said the city and state need to go further.

"We should consider rezoning (neighborhoods in the flood zone) for day use and as recreational areas," said scientist William Fritz, interim president of CUNY College of Staten Island. That change of land use should happen even if homeowners in the flood-prone areas object, Mr. Fritz added.

"New York Harbor is the most dangerous point on the Eastern seaboard," he said. Sea levels here have risen steadily by one foot per century for the last 5,000 years. But we may be looking at a rise between two and five feet over the next century, he said.

In lower Manhattan — an area that won't be willingly given back to Mother Nature — some commercial office towers are planning for the next flood by building "submarine doors." Tishman Construction is planning to add the water-sealed doors to the tower rising at 1 World Trade Center, which flooded with 20 feet of water during the October storm.

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"Submarine doors will be a feature going with a concrete core," said Jay Badame, CEO of Tishman Construction. A spokesman for the Port Authority of New York and New Jersey said all options were on the table but that they had not committed to anything, yet.

Keeping employees on the job will be another important part of storm response, conference participants said. At the Metropolitan Transportation Authority, employees were encouraged to sell back vacation days and donate them to coworkers who lost their homes, said acting chief Tom Prendergast.

Sandy was referred to as the city's first social-media natural disaster. Twitter, Facebook and email alerts played a major role in how the city and state dispatched emergency messages during the storm. But expanding broadband access is a priority in rebuilding, said Andrew Rasiej, the chairman of New York Tech Meetup, a 30,000-member organization. Currently, a third of the city's population can't afford to get online, he said. The cost of broadband, somewhere between $80 and $90 a month, needs to be lowered to make it more affordable.

Seth Pinsky, president of the city's Economic Development Corp., who is heading up the city's response team, cautioned that the next natural disaster to hit the city won't look anything like Sandy. He ticked off other ways climate change could cripple the city: "Heat waves, drought, heavy downpours and wind events." The number of New York buildings in an inundation zone was 88,000, he said. Under new FEMA flood maps, the number of buildings in flood zones for New York and New Jersey could be increased by another 65,000.

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Other speakers said the city's post-9/11 response offered some lessons on how to react to Sandy.

"The Lower Manhattan Development Corp. is an authority people love to hate," said Carl Weisbrod, a partner at HR&A Advisors Inc. That city and state agency was created immediately after Sept. 11, 2001, to coordinate the rebuilding of lower Manhattan but has been criticized for outliving its usefulness and adding another layer of bureaucracy to an alphabet soup of agencies working downtown.

But Mr. Weisbrod said the development agency was useful. "It acted as a forum for making decisions for the city and the state…a lot of good came out of that," Mr. Weisbrod said. "It's important to see here the need for similar or greater cooperation."

Clarification: The number of New York buildings in an inundation zone was 88,000, he said. Under new FEMA flood maps, the number of buildings in flood zones for New York and New Jersey could be increased by another 65,000. The location of the buildings was not clear in an earlier version of this article, published April 4, 2013.

Annie Karni writes for Crain's New York Business, a sister publication of Business Insurance.