New York City, a climate change leader, challenges enlarged flood maps

By Evan Lehmann | 09/08/2015 07:59 AM EDT

New York City and dozens of other communities that were flooded during Superstorm Sandy are challenging the government’s updated flood maps showing expansions of flood risk areas where thousands of buildings could be damaged.

New York City and dozens of other communities that were flooded during Superstorm Sandy are challenging the government’s updated flood maps showing expansions of flood risk areas where thousands of buildings could be damaged.

The Federal Emergency Management Agency has received appeals and comments from about 190 communities in New Jersey and New York since the agency began issuing preliminary flood maps earlier this year, according to Andrew Martin, a spokesman in FEMA’s New York office. New maps have been issued for more than 200 municipalities in the two states.

The most sophisticated challenge is coming from New York City, which contends in a 180-page report that FEMA’s new maps overestimate the height of flood levels by up to 2 ½ feet. City officials say that mistakenly affects 26,500 buildings and 170,000 people by including them in areas susceptible to a 100-year storm, where the purchase of federal flood insurance is required for mortgage holders.


The objections highlight the challenges FEMA faces when modernizing old maps in an era of quickly changing perils. This is the first time since 1983 that the agency has analyzed the region’s flood risk, even as new development and climate change are altering rainfall, sea levels and the characteristics of runoff, experts say.

Sandy flooding
Avenue C in lower Manhattan suddenly become waterfront the night of Oct. 29, 2012, just before Superstorm Sandy turned out the lights. | Photo by David Shankbone, courtesy of Flickr.

With 30 years between map updates, and potentially several inches of sea-level rise since 1980, the new flood estimates can suddenly draw new homes into the floodplain or raise the cost of flood insurance practically overnight, said Mark Mauriello, a former commissioner of New Jersey’s Department of Environmental Protection.

That can lead to opposition around the new flood insurance rate maps, or FIRMS, whether they’re accurate or not.

"The reality is that the day those maps are produced, the conditions continue to change," Mauriello said of rising seas and other factors. "These changes are occurring much more quickly than they were in the past."

In New York, officials are acknowledging that climate change is contributing to the expansion of the floodplain even as they challenge the new maps, resulting in a sometimes delicate balance. The city’s analysis focuses on technical details of FEMA’s research. It says, for instance, that FEMA overestimates the storm tide of a 1950 nor’easter by more than 4 feet. The agency used the storm to help guide its computer simulations of flood depth, and the city argues that the exaggerated water levels influenced many of FEMA’s conclusions.

Rooting out ‘errors,’ or practicing politics?

At Battery Park, FEMA’s estimate of the 1950 storm means that floodwaters during a current 100-year storm would climb to 11.6 feet, or 1.4 feet above the city’s calculations. That can inflate the price of insurance and require more expensive building techniques, the city says.

"What we found were flaws in how the FIRMS were developed," said Daniel Zarrilli, who runs the city’s Office of Recovery and Resiliency, in an interview. "We’re not saying the floodplains aren’t growing. They clearly are. They’re even growing from what they were from in 1983. The 100-year floodplain just isn’t growing as much as … the preliminary FIRMS say they are."

It’s unclear how the disagreement will be reconciled. FEMA gives communities 90 days to appeal or comment on the preliminary maps. That window is now closed, and the agency hasn’t formally responded to New York’s submission. The final maps won’t be enacted until each community formally adopts them.

FEMA is defending its findings as an accurate interpretation of the flood risks faced by New York. During Sandy, Battery Park saw the storm tide reach 14 feet, an amount that sent water flowing into the streets of the Financial District at depths of 2 to 9 feet.

"My assertion is that our maps as they stand now provide an excellent depiction of flood risk for New York City," said Martin, the FEMA spokesman. "They have used the word ‘error’ and ‘mistake.’ We do not believe we’ve made any errors and mistakes. We believe we followed our guidelines and specifications very closely."

Like many exercises in computer modeling, the results portraying the reach of a 100-year storm can vary according to the information that’s being input into the model. Both FEMA and the city conducted their own modeling and reached sharply different conclusions.

FEMA found that the number of people and buildings susceptible to flooding nearly doubled since 1983, to 400,000 residents and 71,500 buildings today. The city estimates the number of people in the flood zone has grown by 6 percent during that period, to 230,000 residents. It also says there are now 45,000 buildings in the floodplain, a 25 percent increase over 32 years.

City officials are concerned that FEMA’s interpretation will financially harm residents by requiring them to buy flood insurance even though, the city says, they’re outside the 100-year flood zone. Homeowners already within the floodplain could have to pay more for their coverage, which increases with each foot of estimated flood levels.

The federal flood program also requires municipalities to enforce stronger building codes that can protect structures from a 100-year storm. Theoretically, an expansion of the floodplain could also expand those standards into additional areas of the city, potentially raising the cost to build homes. The city, however, has voluntarily exceeded the standards outlined in FEMA’s preliminary maps, by 2 feet.

City sees flood insurance as a ‘blunt’ tool

There is, of course, an alternative scenario to the city’s outlook. After Sandy, which in many places might have been larger than a 100-year event, some residents outside the designated flood zone blamed the federal flood program for not accurately assessing their risk of being inundated. They were flooded, and they said the government should have encouraged them to buy insurance.

In that way, the National Flood Insurance Program is sometimes described as a way to foster climate adaptation. Clear warnings of flood risk, through maps and annual premiums, combined with the program’s requirements for stronger building codes can reduce damage, supporters say.

New York City, however, is concentrating on more tangible efforts. Zarrilli said flood insurance is a "blunt" tool to manage risks. Instead, officials are trying to prevent flooding in the first place through a series of proposed levees topped with bike trails and parks, flood walls and other engineered defenses. In all, the city plans to spend $20 billion over several decades on resiliency efforts; $3.7 billion is already earmarked for the first phase of coastal defenses.

Zarrilli said this will "buy down" the risk of flooding at a time when the city expects to see between 1 and 2 feet of additional sea-level rise by 2050.

In most places, that would be considered folly, said Eli Lehrer, an insurance expert and president of the conservative R Street Institute. Building expensive infrastructure to protect peril-prone development is rarely cost-effective, he said.

That’s not true in New York City.

"In a place like Manhattan, it may make a lot of sense to invest quite a lot in structural mitigation because of climate change," he said, noting that the city’s "infinitely valuable" real estate could justify spending tens of billions of dollars over the coming decades.

In other words, the city will never be abandoned because of rising seas, no matter how great the cost to protect it. Lehrer said that’s probably not the case with smaller flood-prone towns on the Mississippi River, where "the calculus indicates you should move the town."

For others, the debate about flooding underscores the hazardous building practices undertaken in the United States. Larry Larson, former head of the Association of State Floodplain Managers, applauded New York’s use of elevated building standards, even as he noted that sea-level rise could surpass those requirements during the lifetime of the homes they affect.

"There’s no magic answer to this," Larson said. "Unfortunately, we’ve come down to the point of saying, ‘Here’s the floodplain, let’s show you how to build in it.’ Rather than saying, ‘Here’s the floodplain, avoid it.’"