More Chicago Properties at Risk for Flooding Than Flood Maps Suggest

After the third straight “wettest May on record” for Chicago, if you’re a Chicagoan you may be wondering if your home is at risk for serious flooding. One way to figure this out might be to look at the flood maps provided by the Federal Emergency Management Agency (FEMA), the federal agency in charge of national disaster preparedness and relief. FEMA flood maps say that only 0.3% of properties (three out of every 1,000) should flood more than once every 100 years. If you base your opinion of your home’s flood risk on FEMA flood maps alone, you will probably think your home is safe. However, if you watched the news coverage of the May 2020 storms with images of the Riverwalk underwater, the Willis Tower as a dark obelisk in the skyline after its basement flooded, neighborhood streets turned into rivers, and yards turned into ponds, you may be thinking that risk assessment seems too low, and you’d be right. In this blog, I discuss flooding in Chicago and why FEMA flood maps underrepresent flood risk in Chicago.

What FEMA flood maps miss

Although FEMA performs geological surveys periodically to determine which areas are likely to face flooding during a once-in-100 year flood, the maps FEMA creates from these surveys do not always provide a complete picture of flood risk. In Chicago, there are two primary reasons for this mismatch.

First, when designating flood zones, FEMA does not take into account the primary source of flood risk for most Chicago properties, surface flooding. FEMA’s designation process focuses on flood risk from surging coastal tides and overflowing rivers, but does not consider surface floods, which occur when heavy rainfalls overwhelm local drainage and sewer systems independent of an overflowing body of water. The City of Chicago's combined sewer system is only designed to handle runoff from a once-in-five year storm, which leaves many Chicago neighborhoods particularly susceptible to this type of surface flooding. This means that many Chicago properties that face surface flood risk are likely to be left out of FEMA’s calculations; and only properties located adjacent to Lake Michigan or one of Chicago’s many rivers and canals are likely to be in a FEMA once-in-100 year flood zone.

Second, FEMA flood maps are often outdated: Most of Chicago’s maps were last updated in 2008 and flood risk can change over time. One expected driver of increased flood risk in the Midwest is climate change. Scientists from the Environmental Policy and Law Center predict that springs in the Great Lakes will become increasingly wetter over the course of the next century, and heavy rainfalls, such as those that produce surface flooding, will occur more frequently and with greater intensity.¹

New land development that increases the amount of impervious cover, such as sidewalks, streets, parking lots, and buildings, and fails to account for stormwater runoff can also increase flood risk. Approximately 60% of Chicago is covered in impervious surfaces, a number that has been increasing marginally over the past decade.² To reduce the impact of development on flood risk, Chicago and the surrounding collar counties have all implemented some form of “green” stormwater infrastructure into their building codes and city planning. Conventional “gray” stormwater infrastructure uses a combination of gutters, curbs, piping, and drains to move stormwater runoff away from impervious surfaces and into collection systems, such as sewers and underground reservoirs. In contrast, green stormwater infrastructure uses systems that mimic nature to capture stormwater where it falls, keeping it out of the sewer system entirely. In Chicago, these green efforts include the installation of rooftop gardens, the use of permeable pavement in alleys and roads, the greening of arterial streets, the planting of native gardens, and the use of rain barrels to capture stormwater.

Other estimates of Chicago flood risk

FEMA flood maps place 0.3% of Chicago properties in a once-in-100 year flood zone, but an alternative measure from First Street Foundation (FSF) estimates that 12.8% of Chicago’s 600,000+ properties may be at risk during a once-in-100 year flood, a difference of 75,623 properties.³ So what explains this difference?

Well, FSF’s methodology for assessing flood-risk differs from FEMA’s both in terms of how flood risk is measured and what types of flood risk are included in that measurement. To create their flood-risk estimate, FSF uses a variety of hydrologic models that study rainfall and stormwater in connection to an area’s geography and geology and hydraulic models that examine the physics of water and in particular, its behavior in sewer and storm systems. The FSF models incorporate historical flood data, along with current geological and climate data to continually assess flood risk at the individual property level. Compare this to FEMA’s approach, which performs costly hands-on geological surveys to periodically assess the flood risk of a given area. Most importantly, unlike FEMA, FSF includes surface-flood risk from heavy rainfall in their flood-risk model, and this explains much of the increase in Chicago’s flood risk under the FSF methodology.

Historical flood-loss data suggests that the FSF methodology more accurately identifies flood risk in Chicago than FEMA flood maps. Two recent studies by the Center for Neighborhood Technology of Cook County (CNT) and the Illinois Department of Natural Resources (IDNR) found little correlation between a property being in a FEMA flood zone and flood damage.⁴ The IDNR study found that 90 percent of flood damage claims between 2007 and 2014 were for properties located outside of the mapped 100‐year floodplain. The overwhelming majority of flood damage claims in Chicago are related to basement flooding, which often occurs when heavy rainfalls overwhelm sewer systems that then back up and send raw sewage into peoples’ homes.

While basement flooding doesn’t draw the same media attention as videos of people stuck on rooftops awaiting rescue, the economic costs and impacts on mental and physical health and safety can be significant. Flooding has cost Illinois over $3 billion in damages between 2000 and 2018, more than any other state outside of the hurricane-plagued Gulf Coast.⁵ For homeowners, surface floods that inundate properties can damage foundations, which may require costly remediation to repair. And if basement flooding occurs because of sewage backup, in addition to the costs of replacing damaged items, furniture, and drywall, cleanup costs to remove standing water and sewage can be substantial and the process can be quite distressing. There are harrowing stories from Chicago residents in the Southside neighborhood of Chatham coming home to the stench of knee-deep sewage waste and opening up their basement door to a buzzing swarm of “sewer flies,” whose eggs had washed into their homes during a storm.⁶ Chatham, built in one of the lowest parts of the city, in an area once filled with wetlands known as “Hogs Swamp,” is one of the many Chicago neighborhoods located outside of a FEMA flood zone that shows significant flood risk in the FSF methodology.

Table 1 shows the concentration of Chicago’s flood risk by zip code ordered by the number of properties with a once-in-100 year flood risk as modeled by FSF. According to the FSF model, flood risk in Chicago is concentrated in a few zip codes: 75% of Chicago’s once-in-100 year flood-risk properties reside in 15 of Chicago’s 64 zip codes, and these zip codes are home to 43% of Chicago’s total properties. Properties with the highest risk of flooding are even more concentrated; the same 15 zip codes contain 93% of properties with once-in-20 year flood risk, which is equivalent to a 5% chance of flooding in any given year.

1. Chicago zip codes with most properties in 1-100 year flood zone

Flood risk in Chicago is not just concentrated geographically, but it also has a greater impact on minority neighborhoods, many of which face no “traditional” flood risk from overflowing rivers or surging tides. Chicago’s high-flood risk neighborhoods are clustered in Chicago’s South, West, and Southwest sides. Most of these neighborhoods are predominantly African-American and Hispanic. This finding of concentration of flood risk in minority neighborhoods is further supported by an analysis of flood insurance claims data by the Center for Neighborhood Technology (CFNT), which finds that 72% of Chicago’s total flood damage claims between 2007 and 2016 were from predominantly African American or Hispanic neighborhoods.⁷ In addition, unlike the neighborhoods of Albany Park and North Center, which lie along the Chicago River and are home to properties in a FEMA once-in-100 year flood zone, many of the affected minority neighborhoods are located away from any body of water and have no traditional flood risk. Chatham, Englewood, Douglas Park, and Back of the Yards, all of which have populations that are more than 80% African American or Hispanic (see table 1), are not located near any waterway and have some of the greatest flood risk in the city. According to CFNT, the affected neighborhoods also have median incomes that are lower than average, making it more difficult for households to pay for necessary repairs and cleanup.

What residents can do about flood risk

Most home and renters insurance policies do not cover damages from floods, but a separate flood insurance policy can help with the costs associated with cleanup and repairs following a flood. Homeowners with a mortgage who reside in a designated once-in-100 year flood zone are generally required to purchase flood insurance by their lenders through the National Flood Insurance Program (NFIP). However, even if a home is outside of a FEMA flood zone, a homeowner or renter can still purchase a flood insurance policy through the NFIP, usually at a reduced rate. However, most Chicagoans who insure against the cost of flooding do so by purchasing a rider on their existing home-insurance policy. These riders typically cover sewage backup and basement seepage and provide $5,000 to $10,000 after a deductible for cleanup costs, repairs, and damaged items. As a renter in Chicago, you would likely be on the hook for any damages to electronics, furniture, or other items due to flooding, as well as the costs of alternative lodging like a hotel room, if flooding makes your apartment uninhabitable. For these reasons, renters in Chicago, especially anyone in a “garden” apartment, might want to consider a flood insurance policy.

Home flood mitigation infrastructure like basement sump-pumps and drainage systems can help prevent buildup of storm waters in a home, but since everyone shares the same sewer system, flood mitigation in Chicago is largely a community effort. The Metropolitan Water Reclamation District of Greater Chicago has been encouraging investment in green infrastructure to keep stormwater out of sewers. In this vein, some residents have taken to replacing their lawns with native plants and grasses to better absorb rainwater and installing rain barrels to capture rain, but the city is also undertaking some large-scale gray infrastructure projects to increase the capacity of the sewer system during heavy storms.

In the mid-1970s, Chicago began one of the nation’s longest running–and most expensive—public works projects that is still under construction today, the 109-mile long Deep Tunnel. The Deep Tunnel is massive snaking labyrinth of subway-sized tunnels that run under the city and is designed to carry storm runoff from local sewer systems into three suburban wastewater reservoirs. The project is expected to be completed in 2029, and parts of the system are already operational. However, the Deep Tunnel will not fix all of Chicago’s flooding problems. Some hydrologists argue that this massive system will still be unable to handle the wastewater from a once-in-50 year storm even after completion. This is because many of the local sewer systems are unable to drain stormwater quickly enough into the Deep Tunnel; one engineer described draining water from some local sewer systems into the Deep Tunnel as “emptying a bathtub with a straw.”⁸

The City’s long-running “Rainblocker” program is another (sometimes controversial) attempt to keep stormwater out of the sewer system. The city has installed nearly 200,000 inlet restrictors or “Rainblockers” on street drains, which prevent stormwater from entering sewers, leaving it to pool up in the streets. However, in some areas this has done more than make it annoying to cross the street after a storm. The pooled water has poured over curbs and into residents’ homes. This all highlights the fact that there is no simple solution to preventing surface flooding in Chicago. Managing flood risk is a difficult and interconnected process, requiring coordination and investment across households, neighborhoods, and communities.

The future of Chicago flood risk

Chicago faces far greater flood risk than most parts of the country outside of the Gulf Coast, but FEMA flood maps do not fully capture these risks. Climate change could well exacerbate Chicago’s flooding problems in the coming decades, as storms that quickly drop inches of precipitation capable of overwhelming sewer systems become more frequent and intense. Chicago has undertaken ambitious gray infrastructure projects, such as the Deep Tunnel, that should alleviate some flooding issues, but more work needs to be done in developing green infrastructure to keep stormwater out of the sewer system to begin with. For individual homeowners, rain barrels and native gardens may help to reduce stormwater runoff, and flood insurance can be used to limit the financial loss from flooding.

---

Notes

¹ More details online.

² More details online.

³ Data from First Street Foundation and their property level flood-risk website.

⁴ CNT study, and IDNR study.

⁵ Details online.

⁶ Details online.

⁷ Details online.

⁸ More information online.

---

The views expressed in this post are our own and do not reflect those of the Federal Reserve Bank of Chicago or the Federal Reserve System.