A person holding an umbrella walks down a flooded street in Hoboken, New Jersey.
A person walks down a flooded street in Hoboken, New Jersey. Gary Hershorn/Reuters

When flooding occurs in a small town or just part of a city, it doesn’t register like a big disaster does, according to the first-ever nationwide assessment.

When a major city like Houston or Detroit floods, the nation pays attention. The president may declare a state of emergency, and agencies at all levels of the government begin recovery efforts while monitoring the event. When flooding happens in a small town or only a small part of a city, though, the event may not be closely examined for its economic and social damages.

That dearth of data is why researchers behind the the first-ever nationwide assessment of urban flooding call the issue the country’s “hidden challenge.”

Researchers at the University of Maryland and Texas A&M University surveyed professionals involved in public and private flood management from more than 350 municipalities in 48 states. Eighty-three percent of respondents said they’d experienced urban flooding in their communities. Over half said their communities were affected by moderate or larger urban floods. While major hurricanes like Florence and Michael command our attention, the researchers’ review of online news alerts found that multiple flooding events happen almost daily. Searches of reports from the National Weather Service for the terms “urban flooding” and “street flooding” resulted in more than 3,600 entries between 1993 and 2017 from all regions of the country.

“It gnaws away in so many places, and it doesn’t [always] rise to the level of a big Mississippi River flood or a [Hurricane] Harvey in downtown Houston,” said Gerry Galloway of the University of Maryland, who co-authored the report. Yet there isn’t nearly enough information to help government officials understand the extent of these floods. Part of the problem, the authors note, is that there is no single federal agency that collects and evaluates urban flooding as it occurs or over time. And because the threat of coastal floods often overshadows that of urban floods, there has been little effort to distinguish between the two kinds of events.

Galloway says the social costs, in particular, are neglected. Researchers know that urban floods disproportionately hurt lower-income communities that have the least resources, but it’s difficult to put a firm number to the problem. According to the report, they’re more likely to live in high-risk flood zones but less likely to have flood insurance.

They’re also more badly hurt by what the researchers call “secondary effects,” such as the loss of hourly wages when a flood prevents them for getting to work, or the hours lost to traffic rerouting. Galloway uses an analogy: “If you have one pair of shoes and they get soaked, you don’t go to school that day,” he said. “You may not get the meals you normally get for breakfast and lunch.” These effects might seem minor, but they add up.

When the consequences of urban flooding are written off, it often means that communities are not proactive about it. One thing is for sure: Urban floods are largely a result of the human-built environment (both CityLab and The Atlantic have previously reported on this). In the survey, 70 percent of respondents reported that aging and inadequate drainage systems were their main problems when it comes to flooding. Of those respondents, more than half said their communities failed make proper infrastructure improvements to withstand increasing levels of rainfall—which has on average risen roughly 4 percent across the U.S. since 1901, with the Northeastern and Midwestern regions experiencing the largest hikes.

Observed changes in heavy precipitation since 1901 reveal as much as a 40 percent increase in rainfall in some parts of the U.S. (Climate Science Special Report)

Not surprisingly, the inability to secure funding accounts for much of that failure. In one anonymous comment submitted, the respondent noted that while their city has proper protection against coastal flooding, getting funding to retrofit drainage systems has been a challenge. “The non-glamorous infrastructure needs to compete with more visible public enhancement efforts for the limited dollars available and unfortunately more often than not fail to get funded,” the respondent wrote. Researchers also note that low building standards in some communities and the lack of code enforcement in others further exacerbate the problem.

The report calls on governments at all levels to review their responsibilities when it comes to evaluating and mitigating the consequences of urban floods. Municipalities need to thoroughly study where exactly floods happen, since urban flooding often occurs outside of FEMA-designated floodplains. As a result, developers continue to build in flood-prone areas, leaving residents blindsided. (As the authors note, approximately 25 percent of all claims submitted to the National Flood Insurance Program involve property outside of the 100-year flood zone.)

The report’s co-author Sam Brody, director of the Center for Texas Beaches and Shores at Texas A&M, is building on this assessment and preparing for a two-year, $3-million project to better map urban flooding, funded by FEMA, the National Academy of Sciences, and Texas. “We’re going to really nail down who’s at risk and what to do about it, by collecting not just claims and federal assistance [data] but looking at crowdsourcing data, human surveys, and then going into communities with a map and [asking,] ‘Why is this wrong?’” Brody said. “The local knowledge is going to feed back into our statistical spatial models and recalibrate them.” Although the project’s location hasn’t been finalized, Brody said his team will likely look at neighborhoods south and southeast of Houston.

The hope is not only to paint a clearer picture of urban flooding, but to illustrate for other cities how that can be done and how they can better communicate risks and mitigation strategies to residents. Brody points to his department’s BuyersBeWhere website—sort of a Zillow-meets-flood-risk map—as a possible tool cities can recreate with the right resources. The federal and state governments will have to get involved too, by providing not just funding, but also data and skilled researchers to help cities do their own analysis.

“It’s never too late to address this issue that’s just going to become worse over time,” Brody said. “We can always do more.”

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