{"id":392002,"date":"2026-07-30T14:01:14","date_gmt":"2026-07-30T14:01:14","guid":{"rendered":"https:\/\/www.newsbeep.com\/us-tx\/392002\/"},"modified":"2026-07-30T14:01:14","modified_gmt":"2026-07-30T14:01:14","slug":"fema-floodmaps-underestimate-flood-risk-by-over-200k-new-study-shows","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/us-tx\/392002\/","title":{"rendered":"FEMA floodmaps underestimate flood risk by over 200K, new study shows"},"content":{"rendered":"

In Harris County, the number of properties facing 100-year-level flood risk<\/a> may be more than twice as large as\u00a0FEMA\u2019s current maps suggest, according to a Texas A&M University study.<\/p>\n

For the past decade, flood researchers at the university\u2019s Institute for a Disaster Resilient Texas<\/a> have worked to develop a tool that offers disaster risk information to property owners across dozens of counties impacted by Hurricane Harvey in 2017. Using detailed federal insurance claims data not available to the public, they built the model based on where flooding has historically caused damage.\u00a0<\/p>\n

Despite increasingly advanced climate science, many homebuyers are still left without a clear picture of the risk they may be taking on, said Sam Brody, the institute\u2019s director and the lead technical expert on Gov. Greg Abbott\u2019s post-Harvey commission.<\/p>\n

FEMA\u2019s maps for Harris County are decades out of date, and their long-awaited replacements<\/a> will likely take years to finalize. Meanwhile, state disclosure laws still leave significant gaps, and some major real estate platforms have resisted<\/a> publishing independent climate risk estimates.<\/p>\n

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\u201cEvery time I gave a talk in Texas, people would come up to me afterward and say, \u2018I wish I had known these things, and I would not have bought my house, but now I\u2019m stuck.\u2019 Or I\u2019d hear, \u2018I\u2019ve lived in my house for 30 years. I never flooded, and now I\u2019m flooding. Can you tell me why?\u2019\u2019 Brody said. \u201cI realized we had enough data and knowledge to tell people their risk.\u201d<\/p>\n

Overall, FEMA places about 184,800 county properties in its regulatory floodplain \u2014 areas with at least a 1% annual chance of flooding. The IDRT model, on the other hand, estimates that about 389,500 properties have at least a 1% annual chance of sustaining flood damage.\u00a0<\/p>\n

That figure is closer to the 345,400 properties that would fall inside FEMA\u2019s regulatory floodplain under a new set of maps released by the federal agency in February. The proposed maps would mark the first comprehensive update<\/a> to Harris County\u2019s floodplain boundaries in two decades, but local officials said they could still take years to finalize.<\/p>\n

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The Houston Chronicle has integrated the IDRT tool\u2019s Harris County data into a searchable map<\/a> that allows residents to enter an address and see the property\u2019s estimated flood risk. Readers can also visit the researchers\u2019 Buyers Aware platform<\/a> to explore flood hazards in other counties.<\/p>\n

Like any model, the Texas A&M researchers\u2019 approach has strengths and limitations, according to multiple independent climate risk experts.<\/p>\n

A key advantage, they said, is that it draws on actual flood damage claims rather than relying on engineering assumptions about how water moves, as FEMA and many commercial flood-risk apps do.<\/p>\n

\u201cThe concept of a floodplain makes sense in places that have a river, then a floodplain, then hills and mountains beyond that. It\u2019s always going to flood in roughly the same place,\u201d said James Dolls-Gollins, a civil and environmental engineering professor at Rice University. \u201cBut Houston is very flat, with a lot of concrete, and gets torrential rain, so it can flood anywhere.\u201d<\/p>\n

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With the IDRT model, \u201cyou get to bypass a lot of the assumptions because you\u2019re actually looking at real events,\u201d Dolls-Gollins said.<\/p>\n

How the model works<\/p>\n

The idea for Buyers Aware started, in part, because Brody was tired of being asked by relatives and friends if their houses would flood. \u201cI can automate this,\u201d he remembered thinking.<\/p>\n

So one weekend in 2016, a former student flew into Houston, and the two got to work. Together they figured out how to turn flood data Brody had gathered from previous projects into something the public could use.\u00a0<\/p>\n

SEARCHABLE MAP: Is your Houston home outside of the floodplain? New research says think again.<\/a><\/p>\n

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By the end of the weekend, they had built a rudimentary version of what would become Buyers Aware. It covered only Harris County and looked little like today\u2019s tool. Still, people found it. Following one storm that year, the site drew roughly 30,000 views in a week, Brody said.<\/p>\n

Then Harvey hit, and the project received millions in state funding. That allowed the team to hire staff, expand to more counties and obtain more claims, elevation data and soil data to build the machine-learning algorithm that is now the basis of its flood risk assessments.<\/p>\n

The algorithm learns how seven property-level factors are associated with historical flood insurance claims, and then uses those patterns to estimate flood hazards for other properties. Below are the seven factors it analyzes.<\/p>\n

Seven risk factors that can determine your flood risk<\/p>\n

\nElevation<\/p>\n

Lower-lying areas are more likely to collect water or sit in the path of runoff.<\/p>\n

\nDistance to coast<\/p>\n

Properties closer to the coast face greater exposure to storm surge and high tides and generally have higher flood risk.<\/p>\n

\nHeight above nearest drainage<\/p>\n

Those with less vertical separation from nearby drainage points \u2013 such as a stream, lake or coastline \u2013 are more vulnerable to rising water.<\/p>\n

\nLand roughness<\/p>\n

Vegetation and other land cover around the property resist and slow down moving water. Smoother surfaces provide less resistance to runoff, which can allow water to move more quickly and increase flood risk.<\/p>\n

\nSoil drainage<\/p>\n

How quickly water can move through the soil when saturated. Water that drains more slowly is more likely to remain at or near the surface, increasing the likelihood of flooding.<\/p>\n

\nImperviousness<\/p>\n

The share of surrounding land covered by urban impervious surfaces such as pavement, buildings and concrete that prevent water from soaking into the ground. Impervious cover creates more runoff and can overwhelm drainage systems, increasing a property\u2019s risk.<\/p>\n

Unlike FEMA\u2019s floodplain boundaries \u2013 which divide properties into those inside or outside a certain designated flood zone \u2013 the IDRT model shows risk on a continuum.<\/p>\n

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When the two models display different levels of risk,\u00a0Brody said residents should still heed FEMA\u2019s designation because it determines whether a homeowner must carry flood insurance and other requirements.<\/p>\n

Understanding Flood Risk Levels<\/p>\n

\nFloodway<\/p>\n

Rivers, bayous and adjacent land where water flows most forcefully during storms. Development is usually heavily restricted in these areas.<\/p>\n

\n100-Year Floodplain<\/p>\n

Areas with a 1% chance of flooding in any given year. In Harris County, these properties could flood with about 17 inches of rain in 24 hours. Significant risk over a typical 30-year mortgage period.<\/p>\n

\n500-Year Floodplain<\/p>\n

Areas with a 0.2% annual chance of flooding. Houston experienced three “500-year floods” from 2015 to 2017, including Hurricane Harvey.<\/p>\n

Note: With climate change intensifying storms, these historical risk calculations may underestimate current flood dangers. Learn more here<\/a>.<\/p>\n

A higher degree of risk on Buyers Aware can be a reason to look more closely at a property and consider added protections, from buying flood insurance to improving drainage, adding flood vents, sealing entry points or, in more extreme cases, elevating a home. A lower risk level, meanwhile, could offer some reassurance about a property\u2019s level of safety, he said.<\/p>\n

A FEMA spokesperson acknowledged the agency\u2019s maps do not capture every place that could flood. Third-party tools use different data and methods and can provide complementary information.<\/p>\n

\u201cIt\u2019s very important to recognize that flooding happens everywhere and can occur outside high-risk areas,\u201d the spokesperson said. \u201cWhile maps help communities manage risk, they do not guarantee that flooding will not happen outside of these boundaries.\u201d<\/p>\n

A growing field<\/p>\n

For homebuyers, piecing together a property\u2019s flood history can often be daunting and sometimes impossible, experts said.<\/p>\n

Texas law requires sellers to disclose information, such as if a home is in a floodplain, has flooded before or has been the subject of a flood insurance claim. But the law has limits.<\/p>\n

An owner who has held a property only briefly, for instance, does not have to disclose flooding that occurred before they owned it or pass along details provided by a previous seller. There is also no central database preserving those disclosures as homes change hands.<\/p>\n

At the same time, FEMA maps, one of the main tools available to the public, were primarily designed to help determine insurance requirements and guide development regulations, not to communicate individual properties\u2019 flood risk to the public, several researchers said.<\/p>\n

Brody\u2019s team is one of a growing number of organizations trying to fill that gap.\u00a0<\/p>\n

MIND THE GAP: Harris County finally has new drafts of FEMA flood maps. Here’s what they’re still missing.<\/a><\/p>\n

Many academic groups, nonprofits and private companies have developed their own tools. And each approach comes with trade-offs, according to Brett Sanders, a civil and environmental engineering professor at the University of California, Irvine.<\/p>\n

In a 2024 paper<\/a> he co-authored, Sanders and his colleagues examined the flood hazard data used by First Street, one of the most well-known climate risk companies in the U.S.<\/p>\n

The researchers found \u201cconcerning levels of uncertainty\u201d in First Street\u2019s data at the municipal and property levels, warning that these national-scale models may miss important local conditions such as small differences in the landscape, drainage systems and flood control infrastructure.<\/p>\n

That is part of the appeal of the Texas A&M researchers\u2019 approach, Sanders said. The algorithm sidesteps the kind of uncertainties engineering models must account for \u2014 from predicting how much rain will fall and where the water will go to how much damage it may cause and minute local factors that can be tricky to capture.<\/p>\n

\u201cIt\u2019s a really promising approach,\u201d Sanders said. \u201cMachine learning methods really work well when you have good data and when you can have a lot of data. So it may be that Houston\u2019s a good place for this because it has a history of flooding.\u201d<\/p>\n

Lisa Knoll, First Street\u2019s chief marketing officer, defended the company\u2019s work, saying it uses high-resolution elevation data and incorporates levees, flood walls and other flood control measures.<\/p>\n

But Knoll acknowledged that national models cannot fully capture some highly localized conditions, particularly in dense urban areas where street-level drainage systems can influence flooding.<\/p>\n

While the IDRT model is not constrained by those uncertainties, the same reliance on real-world claims that sets it apart might also create potential blind spots in the data, some researchers said.<\/p>\n

Because the model learns from properties that flooded and filed insurance claims, its predictions may be less certain in neighborhoods where far fewer homeowners have flood insurance, said James Doss-Gollin, the Rice University professor.<\/p>\n

\u201cLots of people don\u2019t have flood insurance, so that\u2019s a big limitation,\u201d Doss-Gollin said.<\/p>\n

Brody said Texas floods frequently enough that his team has enough data to compensate for the limitation, and they have tested whether the properties represented in its data systematically differ on factors used by the model, such as elevation and impervious surfaces.<\/p>\n

\u201cIn Texas, it is so saturated. We have more data than we know what to do with,\u201d Brody said. \u201cBut we can always have better data and more data.\u201d<\/p>\n

The transparency gap<\/p>\n

Experts say the Texas A&M researchers have been unusually transparent about how their model works, and its limitations.<\/p>\n

That is far from the norm in today\u2019s climate risk research, according to Adam Pollack, an Iowa University professor focused on flood risk management.<\/p>\n

In a 2026 paper<\/a> led by Pollack, researchers examined over 250 highly cited climate risk studies published in 2021 and 2022 and found that only 4% fully shared both their data and code.<\/p>\n

He said that was one reason he preferred the IDRT\u2019s approach to many commercial products \u2013 including First Street\u2019s \u2013 whose underlying methods can be harder for outside researchers to scrutinize.<\/p>\n

\u201cWe\u2019re so lucky that it\u2019s being transparent about its limitations,\u201d Pollack said, pointing to the peer-reviewed paper laying out the Texas A&M researchers\u2019 methodology and performance tests, as well as disclaimers throughout the Buyers Aware website.<\/p>\n

But it has been challenging to get IDRT\u2019s app directly in front of homebuyers.<\/p>\n

Brody\u2019s institute spent about two years working with the Houston Association of Realtors to integrate its flood risk estimates into HAR.com<\/a> \u2013 the association\u2019s home search portal and one of the most widely used real estate websites in Texas.<\/p>\n

Last year, however, shortly before the project\u2019s planned launch, the association abandoned the efforts<\/a> amid complaints from real estate agents who questioned high-risk ratings on some properties and worried they could hurt sales.<\/p>\n

Bill Baldwin, the association\u2019s spokesperson, told the Chronicle at the time that leaders simply could not convince enough members that it was the right time to display the risk ratings directly on listings.\u00a0<\/p>\n

A flood protection advocate himself, Baldwin nevertheless said he believes pressure to make such information more accessible will only grow.<\/p>\n

\u201cThe consumer adamantly wants this information,\u201d he told the Chronicle. \u201cThey\u2019re going to find the information somewhere.\u201d<\/p>\n

For Pollack, tools like Buyers Aware show why improving the science is only part of the equation. The other challenge, he said, is making that information accessible and useful enough to guide real-world decisions.<\/p>\n

\u201cFlood risk is really uncertain,\u201d Pollack said. \u201cBut we can make good decisions in the face of uncertainty.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"In Harris County, the number of properties facing 100-year-level flood risk may be more than twice as large…\n","protected":false},"author":2,"featured_media":392003,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[56,58,57],"class_list":["post-392002","post","type-post","status-publish","format-standard","has-post-thumbnail","category-houston","tag-houston","tag-houston-headlines","tag-houston-news"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/us-tx\/wp-json\/wp\/v2\/posts\/392002","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/us-tx\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/us-tx\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us-tx\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us-tx\/wp-json\/wp\/v2\/comments?post=392002"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/us-tx\/wp-json\/wp\/v2\/posts\/392002\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us-tx\/wp-json\/wp\/v2\/media\/392003"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/us-tx\/wp-json\/wp\/v2\/media?parent=392002"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us-tx\/wp-json\/wp\/v2\/categories?post=392002"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us-tx\/wp-json\/wp\/v2\/tags?post=392002"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}