Urban Flooding: A Doozy of a Problem with a Growing Economic Burden, and a Growing Media Presence

It’s been in the news almost daily: flooding, flooding, and more flooding. But is this new? Or even news? As it turns out, flooding in many parts of the United States has increased substantially over the past century, with greater frequency and volume of rainfall from thunderstorms being a primary driver of this increase since 1979.


Figure 1. Annual precipitation changes vary across the United States, with an average increase in precipitation across the country. The greater frequency of heavy thunderstorms since 1979 have resulted in the greatest increase.

Increased storm frequency and intensity, combined with urbanization and aging stormwater infrastructure, means that urban flooding is news (or at least should be!). The costs of these combined issues are significant, and they have skyrocketed in recent years.


Figure 2. The economic costs of flooding have increased dramatically since 1980.

But first, why is this such a huge problem? We’ve built massive storm sewers to handle this problem and it seems like those systems should just, you know, work. Well, as it turns out, most of our stormwater, wastewater, and combined sewer systems were designed with limited capacity based on populations and rainfall patterns typical of the world in the late 1800s and early 1900s.

In addition, most stormwater systems were designed to handle 5-year storms every 5 years or so.  But we’re now seeing 5-year storms every 2 days in many regions, and our stormwater systems are becoming inundated.


Figure 3. The number of 5-year storms are occurring far more frequently than every 5 years, overwhelming our stormwater systems and causing frequent urban flooding.

Considering the greater number and frequency of storms, and adding aging sewer systems, you’d think that’s enough of an issue. But as you can see in Figure 4, below, increasing development of agricultural lands, i.e., paving over the soil, also plays a large role in increased urban flooding.


Figure 4. Development of agricultural lands closely matches the patterns associated with the number of flood insurance claims in Illinois, for example. How does it compare where you live?

If you think this is a job only for FEMA, think again. Most of the flooding that results from these increasing storms and greater urbanization occurs outside of mapped flood zones. In Cook County, Illinois, for example, over 90% of urban flooding damage claims from 2007 to 2014 were outside the mapped floodplain. This is due in large part to development and impervious surfaces that limit infiltration of rainfall, aging and limited infrastructure that are overwhelmed during rain events, and environmental factors sch as saturated soils resulting from increased frequency and intensity of storms.


Figure 5. FEMA’s flood mapping program is falling behind, while the number, frequency, and location of floods continues to increase.

With more flooding—especially flooding in areas outside the typical floodplain—we see significant economic impacts. In 2016, the city of Baton Rouge was inundated by an estimated 1,000-year rainfall event that flooded 48,000 structures and created over $1 billion in property damage. City officials pointed to the need to understand and expand the community stormwater capacity.

In May 2018, Ellicott City, Maryland was hit by a second estimated 1,000-year rainfall event in 2 years and also suffered more than $1 billion dollars in damages. In June 2018, 8 inches of rain fell in 4 hours on Ankeny, Iowa, flooding over 2,000 homes. The assessment of those losses has not yet been completed.

Most losses are calculated based on claims for flood insurance; however, many of these claims cover only partial damages, and many families and businesses who suffer damages from urban flooding don’t have flood insurance, because they live outside the floodplain, so they are not included in these statistics.

The total cost of urban flooding has not been accurately recorded for several reasons: such floods occur frequently, they are scattered in neighborhoods throughout communities, they do not rise in total economic costs to the level of major events, and they are often not reported; in other words, they are not “news.” But we can do a quick assessment of what constitutes some short-term losses due to floods:

  • Loss of human life
  • Property damage
  • Destruction of crops and loss of livestock
  • Illness due to waterborne diseases (all that sewage…ugh)
  • Communication losses
  • Damages to power plants, roads, and bridges
  • Business closures

Longer term, we see:

While many of the flood damages we see reported are so enormous that it’s hard to fathom on a personal level (see Figure 2, for example), breaking down the impacts to those aspects of life that we hold dearly really brings home the true cost of urban flooding.

The Illinois Department of Natural Resources sums it up well:

Urban flooding is characterized “…by its repetitive, costly, and systemic impacts on communities…These impacts include damage to buildings and infrastructure, economic disruption, and negative effects on health and safety.”

The fact is that urban flooding is happening, it’s getting worse, the impacts are significant, and dammit it’s newsworthy! The solutions are complex, but they need to be based on real data collected in real time from our communities. That’s where StormSensor comes in. We would love to work with you and your city to build a sustainable future based on economic strength…and we can do it, in large part, by providing the data and insights you need to truly understand and manage your stormwater and combined sewer systems.

Is flash flooding a daily news flash in your city? Contact us for a free demo about how we can help!

About the author

Erin Rothman

Talk stormwater with erin@stormsensor.io With more than 15 years of environmental consulting experience, Erin observed so many opportunities for innovation in the stormwater industry. With those in mind, she founded StormSensor to enthusiastically embrace new technology to help solve the problems of an age-old industry.