Flooding in Illinois is on the Rise – Here’s Why

In a quick search of the climate change issues hitting Illinois hardest right now, an increase in floods is among the top contenders.

This is due to a number of factors, according to Trent Ford, the state climatologist for Illinois.

“The root causes of increased flooding due to climate change in Illinois are increased rainfall and rainfall intensity,” Ford said. “It’s gotten wetter across the state every season, and more water overall means a higher chance of water-logged soil and increased runoff.”

This kind of flooding, the kind that is directly related to an increase in the frequency and intensity of rainfall, is referred to as “fluvial flooding.” We see the impact of increased and prolonged wet seasons on our biggest rivers and water systems, which, without sufficient dry weather to regulate themselves, can become overwhelmed and flood.

“Land use plays a really important role in that type of flooding as well,” Ford said. According to Ford, land that is overdeveloped or “impervious” to rain –– such as barren soil as opposed to soil with actively growing crops –– will create more runoff, resulting in more water into streams and rivers.

Given existing trends that indicate rainfall will continue increasing, Ford suggests that the peak level of streamflow in Illinois’ rivers will continue to be higher, as well.

In addition to fluvial flooding, urban or “pluvial” flooding is another part of the equation. This refers to the flooding that occurs within an urban area when there is intense rainfall over a period of several hours, overwhelming the capacity of the drainage system in that area.

“Anybody who lives in Chicago for more than a few years has seen this in some cases many times where it may be dry ahead of time, but we get three or four inches of rain or in some cases, seven or eight inches of rain in just a single day,” Ford said. “The stormwater drainage system backs up, people’s basements get flooded.”

This type of flooding is primarily due to the increased intensity of storms as opposed to increased frequency, which is a direct result of climate change, according to Ford.

In addressing both of these issues, Ford says it’s important to keep in mind that communities that are already in vulnerable positions geographically or financially will see the effects hardest and first.

“The rainfall may be increasing, the flooding may be increasing, but the floods look a lot like floods of the past,” Ford said. “The impacts are felt disproportionately by the poorest and most vulnerable communities… What climate change is doing is not creating a whole lot of new problems, but worsening pre-existing, disproportionate impacts that are built into urban planning.”