When Patrice and Philip Morgan bought a house near the ocean in Brooklyn, they were not particularly worried about the threat of flooding.

Federal maps showed their home was outside the area at a high risk of flood damage. For that reason, the government did not require them to buy flood insurance, a cost imposed on neighbors on more vulnerable blocks.

Even so, the couple decided to raise their house four feet to protect their basement from the effects of heavy rain storms.

“We thought we might have a foot or two of water,” Patrice said, “so we put a sump pump in to avoid any small issues.”

But the maps drawn up by the Federal Emergency Management Agency were wrong. And government officials knew it.

According to documents and interviews, state, local and federal officials had been aware for years that the crucial maps of flood risks were inaccurate; some feared they understated the dangers in New York City’s low-lying areas.

The flaws in the maps had significant impact. Developers relied on FEMA’s assessment of risks when they built new homes near the water. And homeowners and businesses made crucial decisions about where to buy or lease property on the assurance that they were outside of the high-risk zones.

Thousands of the buildings incorrectly identified as outside the flood zone were damaged when seawater surged ashore as Hurricane Sandy made landfall on Oct. 29, 2012.

State and city officials had been asking FEMA for years to revise the maps with technology and modeling methods that didn’t exist when they were first drawn in the 1980s. William S. Nechamen, New York State’s floodplain chief, warned FEMA in a 2005 letter that the failure to do so “will lead to higher than necessary flood damages and more expenses placed on individuals and on FEMA.”

Yet, despite Nechamen’s warning, FEMA missed chances to make changes that could have protected city dwellers from some of the worst of Sandy’s destruction.

Read the rest of the report at Pro Publica.