Record-Breaking May Precipitation Calls for Increased Focus on Climate Change Impacts

As Illinois enters the summer months, we can reflect back on another spring that produced a record-breaking amount of precipitation.

Multiple days of rain in the month of May resulted in widespread flooding across the Chicago region, to the point that the Willis Tower in Chicago was closed for over a week after flooding knocked out the power supply to the building.  On just one day, more than 3.5 inches of rain fell in Chicago.  That was followed three days later with another single-day rainfall exceeding 3 inches.  And this trend continued outside the city, with farmers in Kendall and Grundy Counties reporting flooded properties and ruined crop plantings.

As illustrated below, this one week– May 12th to May 18th– saw precipitation levels 400% to 750% of average precipitation in Northeast Illinois.  Central Illinois also received 200% to 400% of normal rainfall over the same time period.

5.12 - 5.18 rainfall

This is a trend that has persisted the last three years.  As shown below, each of the last three Mays in the Chicago region set a new record for precipitation.  May 2018 observed 8.21 inches of rain, while May 2019 and May 2020 had 8.25 and 9.51 inches of rain, respectively.  The Midwest on the whole has had similar experiences, with rainfall totals in 2019 more than 3 inches above the previous record year of 2018.

Chicago Precipitation in May GraphSource: National Weather Service Forecast Office

While this trend is troubling, it’s not surprising.  As summarized in ILEPI’s past report on climate change and its impact on infrastructure systems in the Midwest, a change in climate is already observable in the Midwest.  The percent of days with “very heavy precipitation” has increased by 27 percent since the 1950s and the average air temperature increased by 4.5 degrees between 1980 and 2010.

And with increased precipitation comes increased flooding, which can pose a variety of risks to Illinois’ vital infrastructure systems.  As these events become more common, transportation infrastructure– including roads, bridges, public transit systems, railroads, airports, ports, and waterways– will be adversely impacted.  Flooding can weaken structural supports for bridges, deteriorate soil that supports roads and bridges, shorten the life expectancy of pavement, and increase sedimentation in waterway channels.  These damages can take months and years to repair and tend to increase maintenance costs.

Additionally, these impacts will be amplified as the consequences of damages disrupt the transportation network and its ability to transport needed goods and people.  Flooding can lead to closed roadways, railroads, and bridges.  Homes and businesses can be cut off from needed supplies.  And inland waterways may be deemed unsafe due to high waters.  This happened just one year ago in 2019, with high water levels on the Mississippi River system forcing barge traffic to a halt due to many locks being closed, which further impacted traffic on the Illinois and Sangamon Rivers.

Local, state, and federal governments should have a renewed focus on climate change as Illinois faces challenges from the shifting climate. Infrastructure, in particular, is susceptible to the long-range impacts of a changing climate because structures have an extended design life that could last anywhere from 20 to 100 years.  As such, mitigation and adaptation strategies should be considered.  These may include strategies to reduce greenhouse gas emissions, creating a climate adaptation plan, re-evaluating infrastructure design strategies, and implementing policies on building in flood-prone locations.  All of these strategies are outlined in ILEPI’s report on Indiana and climate change.

It has now been three years of record-breaking precipitation in Illinois.  While the water has receded, roads have re-opened, and power has been restored to the Willis Tower, these impacts cannot be forgotten.  The state’s climate is changing and this trend is only expected to worsen.  No one policy or action alone will halt the harmful effects of climate change, but actions can and must be made.