New data undermines FEMA flood risk assessments
A new model shows that most Maricopa County properties required to have flood insurance may not face the level of risk determined by local and federal authorities.
According to the Federal Emergency Management Agency, more than 35,000 Maricopa County properties have a 1% chance of annual flooding. But a nonprofit that enlisted dozens of scientists, engineers and researchers has reported that fewer than 600 properties are at such risk.
The federal government uses a 1% annual chance to determine whether homeowners must buy flood insurance. That translates to about a 1-in-4 chance of flood over the lifetime of a 30-yearmortgage, according to a recent USA TODAY investigation.
Large swaths of areas where local authorities have counted hundreds, even thousands, of properties at a 1% risk show none at that threshold in the new data. This includes the north Scottsdale ZIP code of 85255, where FEMA lists nearly 6,300 properties in the flood plain.
The model did find about 1,000 properties there to have at least a 2% chance of flooding, which is “about as likely as being born with 11 fingers or toes,” according to FloodFactor.com.
Hydrologists, researchers and data scientists who developed the model come from a range of institutions including Columbia University, the Massachusetts Institute of Technology and the University of California-Berkeley.
The First Street Foundation, which released the study, combined sea level rise models, riverine flooding and extreme weather simulations to determine flooding risk in all states except Alaska and Hawaii.
It’s difficult to say exactly why the foundation’s model predicts less risk in metro Phoenix than existing floodplain maps. Local planners have yet to examine this, as the data were released June 29.
But Mike Amodeo, the foundation’s director of data science, said a key difference may be that his model projects a much drier year than the government model, based on climate change expectations.
The new model also could weigh the effect of flood mitigation projects differently than local planners do.
But Amodeo said some of the model’s limitations may be at play. The team may be missing some parcels and elevation data can be uncertain in the Southwest.
Our climate makes the region more difficult to assess, too.
“You don’t have a such a steady flow, so when you look at extreme events, there is greater uncertainty around what that would actually be,” he said. “This is an area that is notoriously difficult to get exactly right.”
He encouraged people here to engage with local flood plain managers and public utilities to understand how the systems work.
Authors generally found that FEMA has underestimated the number of properties at risk nationwide, reporting 14.6 million properties facing a 1% annual risk of flooding. FEMA lists just 8.7 million properties in the floodplain.
The largest disparities between FEMA and First Street data were noted in urban areas because FEMA focuses largely on river flooding, while the First Street Foundation researchers considered other flooding sources like storm drain issues, Amodeo said.
Yet, in Arizona, the model identified 10,800 fewer properties than FEMA has for having a 1 percent risk of annual flooding.
The flood insurance question
Anyone can now use the new data at FloodFactor.com to see where their property stands — so Maricopa County Flood Control district staff might soon be hit with demands from homeowners to reassess their floodplain status.
They usually get a handful of requests every year, and they usually determine they were right all along.
So they’re prepared to double up on flood risk education, said Lisa Blyler, spokesperson for the Maricopa County Flood Control District.
Floodplain designation can be controversial because homeowners who live in a floodplain and have federally backed mortgages are required to buy flood insurance.
Amodeo said his team’s Arizona research does not mean those 10,000some property owners should try to shed their flood insurance. Many of them may be in areas that are at risk for flooding, just to a lesser extent than the 1 percent annual marker, he said.
Though flooding doesn’t always come to mind in our arid climate, Arizona actually floods more than other states each year, recording about 40 to 100 floods per year, said Chris Greene, who owns Flood Insurance Guru, an insurance and consulting firm.
Climate change is expected to make weather patterns more erratic and extreme, so more unexpected flooding is likely going to become more frequent, he said.
And living outside of a FEMA-designated floodplain doesn’t mean you’re in the clear: At least 20 percent of flood claims nationwide come from properties outside of high-risk areas, he said.
FEMA and private insurance data on flood plains have historically come up with different results, he said.
A ‘different level of accuracy’
Experts say FEMA is stretched thin and struggles to keep flood maps current, especially for inland areas that may seem less vulnerable than the coasts.
The agency also only uses historical data to determine risk, leaving out current and future models that could point to a changing risk, according to a recent report by USA TODAY.
A FEMA spokesperson in an email wrote that the First Street maps and FEMA Flood Insurance Risk Maps do not conflict with each other, but rather complement one another. The spokesperson encouraged people to explore the differences between the maps to better understand flood risk.
FEMA’s maps and the First Street maps serve different purposes, the spokesperson wrote. FEMA’s data are designed for making decisions about floodplain management or life and safety during a flood event. First Street data can help inform people’s decision to buy flood insurance or take measures to mitigate their personal flood risk, the spokesperson said.
Those two objectives require a “different
Local flood planners said their maps are not out-of-date and they take careful consideration of any nuances that may affect flood risk.
District staff make about 20 to 30 changes to floodplain maps every year, said Cathy Regester, the county’s floodplain permitting division manager.
It can take years to assess an area’s flood risk. District staff start first by analyzing topographic data and and structures such as bridges and culverts. Then they launch a study that involves assessing rainfall data, interviewing residents about flooding they’ve witnessed and developing flood flow rates for the area.
They use computer modeling to determine where flood waters are likely to flow.
Then they go over the results with the relevant public, address comments and send it off to FEMA, which will then go back and forth with questions before approving it. That process takes about a year, Regester said.
They plan to review the First Street Foundation research to understand the root of the differences. They’re already questioning how some homes got left off First Street’s map, particularly some low-lying properties in the Rio Verde area.
And then there are opposite examples. First Street Foundation maps put areas around the McMicken Dam in the Northwest Valley in the risk area, while local engineers consider that dam to adequately contain a 1 percent annual risk of flooding, said Scott Vogel, the flood district’s chief engineer and general manager.
Still, local flood planners welcome the opportunity the new research provides to bring awareness to flooding risk — especially as the monsoon rolls in.
“We’re excited that this kind of detailed information is available to the average person,” Blyler said. “This is providing a great service to a lot of people. It’s just not fitting what we have.”