Flood maps provided by the Federal Emergency Management Agency had traditionally been the go-to tool for analyzing flood risk, but even the agency has acknowledged the value of and shift toward probabilistic models developed by the private sector.

In 2017, FEMA chose the U.S. inland flood and storm surge models of Boston-based catastrophe modeling firm AIR Worldwide, a unit of Verisk Analytics Inc., to assess the National Flood Insurance Program’s overall risk and potential payouts to property owners and help the NFIP evaluate actuarially sound rates and assess the effects of major flooding events in real time.

In the past, underwriting of flood risk has revolved around antiquated government resources such as FEMA’s 100- and 500-year floodplain maps, and the vulnerability of properties was generally determined based on whether they were located inside or outside these zones, experts say.

“Mother Nature doesn’t listen to us,” said Marc Treacy, Chicago-based managing director of flood insurance programs for ISO, a Jersey City, New Jersey-based unit of Verisk. “It stops where it wants to stop. It’s been a push to start thinking about flooding as a true catastrophe, where I don’t think it had been in the past. As we’ve seen more and more losses from flooding, they’re starting to think about it in a similar fashion as they do hurricanes and earthquakes because we need to start planning ahead for it.”

FEMA’s 100-year floodplain maps failed to capture 75% of flood damages from five serious floods from 19992009, none of which reached the threshold of a 100-year event, according to an analysis published by researchers at Rice University and Texas A&M University at Galveston in September.

“They haven’t been revisited in many years. And as populations grow and change, it affects surrounding topography, and the flood risk can be very, very different compared to when those insurance rate maps were originally adopted,” said Jeff Tennis, project team lead for property analytics for Lockton Cos. L.L.C. in Kansas City, Missouri.

“The FEMA mapping has historically been poor, and it’s not necessarily FEMA’s fault,” said John Burkholder, risk and insurance director for Tampa International Airport. “It’s the fact that FEMA’s hands are tied by Congress and they’ve lacked technology to be able to provide good data.”