The maps, drawn by the Federal Emergency Management Agency, dictate the monthly premiums millions of American households pay for flood insurance. They are also designed to give homeowners and buyers the latest understanding of how likely their communities are to flood.
The government's response to the rising need for accurate maps? It's slashed funding for them.
Congress has cut funding for updating flood maps by more than half since 2010, from $221 million down to $100 million this year. And the president's latest budget request would slash funding for mapping even further to $84 million—a drop of 62 percent over the last four years.
In a little-noticed written response to questions from a congressional hearing, FEMA estimated the cuts would delay its map program by three to five years. The program "will continue to make progress, but more homeowners will rely on flood hazard maps that are not current," FEMA wrote.
The cuts have slowed efforts to update flood maps across the country.
In New England, for instance, FEMA is updating coastal maps but has put off updating many flood maps along the region's rivers, said Kerry Bogdan, a senior engineer with FEMA's floodplain mapping program in Boston.
"Unfortunately, without the money to do it, we're limited and our hands are kind of tied," she said.
Many of the flood maps in Vermont—including areas near Lake Champlain that have recently flooded—are decades out of date. "There are definitely communities that really need that data," said Ned Swanberg, the flood hazard mapping coordinator with Vermont's Department of Environmental Conservation.
Asked about the cuts, a spokesman for the White House's Office of Management of Budget directed to us FEMA, which did not respond to our requests for comment.
New maps can guide development toward areas that are less likely to flood. They also tend to be far more accurate. Today's mapmakers can take advantage of technologies including lidar, or laser radar, and ADCIRC, a computer program that's used to model hurricane storm surge. They can also incorporate more years of flooding data into their models.
"It is disconcerting to have counties and areas where people still have maps from the 1970s," said Suzanne Jiwani, a floodplain mapping engineer with Minnesota's Department of Natural Resources.
The slashed funding for the mapping program hasn't gone unnoticed in Congress.
Rep. David E. Price, a North Carolina Democrat on the House Appropriations subcommittee that is responsible for FEMA's budget, told W. Craig Fugate, the FEMA administrator, at a hearing in March 2012 that FEMA's budget "continues to lowball funding" for updating the country's flood maps.
"Both Republican and Democratic Administrations have generally made inadequate requests for Flood Hazard Mapping and Risk Analysis funding, and under the Republican majority funding provided has been inadequate," Price said in a statement to ProPublica.
Andrew High, a spokesman for Price, said the congressman had pushed for modest boost in funding, about $10 million this year.
It was a question from Price that prompted FEMA to detail the delays. FEMA said its ultimate goal was to get 80 percent of the country's flood hazard data up-to-date. Cutting funding for the program "is a difficult decision," FEMA wrote, "but it's reasonable given multitude of competing national priorities and limited resources."
FEMA also funds its maps through the National Flood Insurance Program. It takes a small slice of homeowners' flood insurance premiums, about $150 million in the 2013 fiscal year. But the flood insurance program is also in trouble, and income from the premiums is already stretched thin. The program has more than $20 billion in debt after paying out massive claims after Katrina and Sandy, and it took in only $3.6 billion in premiums last year.
As part of an overhaul to the insurance program last year, Congress authorized the government to spend $400 million a year for the next five years to update flood maps. But for the 2013 fiscal year, Congress has appropriated just a quarter of that. Sequestration has cut another $5 million, according to the Office of Management and Budget, leaving $95 million for flood mapping this year.
That's not nearly enough, said Larry Larson, director emeritus of the Association of State Floodplain Managers, a trade organization based in Madison, Wisconsin.
"To get the mapping done, you need probably $400 million a year for 10 years," Larson said.
The experiences of some homeowners after Sandy illustrate the dangers of outdated flood maps.
FEMA was in the process of updating the maps in New York City and New Jersey when Sandy hit. After the storm, the agency rushed to complete "advisory" flood maps designed to give homeowners a rough idea of how much they might need to raise their damaged homes by to avoid catastrophically high flood insurance premiums—more than $30,000 a year for some homeowners in the worst flood zones.
But homeowners like George Kasimos, whose Toms River, New Jersey, house was damaged in the storm, say they don't want to shell out tens of thousands of dollars to raise their homes until FEMA has finalized the new maps. FEMA plans to release preliminary maps for New Jersey this summer, but the final ones aren't expected until late next year. (Scott Duell, the risk analysis chief for FEMA in New York, said that the cuts had not slowed down work on the new maps in New York and New Jersey.)
Kasimos said any cuts to the flood mapping program were shortsighted.
"There's going to be another hurricane somewhere, there's going to be another disaster," he said. "If you're cutting the flood mapping program, somebody's going to get screwed."