Lake Michigan supply could be affected by climate change
More than 6 1⁄2 million Illinois residents get their drinking water from Lake Michigan. As northeastern Illinois’ supply of groundwater shrinks, more municipalities are considering joining that number. Joliet is the most recent, voting last month to switch in one of the most significant decisions officials said they would make.
Illinois operates well below its Lake Michigan water allocation, but as the state plans for future water use, there is one unknown: climate change.
The planet’s climate is changing at a rapid pace, scientists say, resulting in life-threatening consequences and billion-dollar disasters. In Illinois, that may mean more intense storms, milder winters with more precipitation and hotter, drier summers.
Increased precipitation can affect how much water Illinois can withdraw from Lake Michigan, and runoff can alter water quality. Hot summers correlate to an increase in water demand. Cold snaps, like this month’s stretch of subzero temperatures, pose their own threats when already leaky systems encounter main breaks.
“Climate change brings so much more unpredictability to managing water resources in the region,” said Marc Smith, policy director for the National Wildlife Federation. “Tons of water one year, the next year you’ll get tons of drought. It exacerbates the resource.”
Illinois is governed by a 1967 Supreme Court decree that stems from the reversal of the Chicago River, which long ago sent sewage into Lake Michigan. The state can divert 2.1 billions gallons a day — a figure that includes drinking water from the lake and runoff, like rain that flows into area waterways, among other things.
If climate change continues to produce wetter weather, Illinois may have to factor in that more of its Lake Michigan water allocation will be taken up by runoff even as more municipalities like Joliet tap in.
Mila Marshall, a clean water advocate with the Sierra Club, said Lake Michigan is a finite resource, so we need to have ongoing conversations about capacity and climate change.
“Right now, lake levels are high. Water diversions make sense. But what does it look like when the lake levels are low?”
Conservation efforts and infrastructure improvements may be paying off: The state for years has come in below the maximum diversion, building up a surplus. Accounting is averaged over a 40-year stretch by the U.S. Army Corps of Engineers, and that average has been dropping for nearly three decades.
Runoff averaged about 30% relative to the average diversion, across nearly 40 years. From 2007 to 2017, the average diversion shrunk, but runoff accounted for a greater portion — 39%.
“Long-term climate change has the potential to greatly impact this component of Illinois’ diversion,” a 2012 water supply planning report from the state found.
Runoff is variable, dependent on precipitation in the 673-squaremile watershed. To offset the reversal of the Chicago River, officials count runoff in the watershed against the state’s Lake Michigan total. In 2017, the last year accounting has been completed, runoff made up the largest portion of the diversion at 45%. Public water systems pumping from Lake Michigan, which send drinking water to taps, has generally been the largest.
“I don’t think that there’s cause for concern just yet,” said Jeff Fuller, a hydraulic engineer with the Army Corps, referring to the runoff increase. “Despite seeing increased users coming online with Lake Michigan water as their source, we still see this downward trend for pumpage.”
As for runoff, efforts like building on-site storage and looking for alternatives to pavement that blocks precipitation from making it into the ground aim to lower the total.
The cheapest way to grow water supply is through protecting what’s already there, said Jason Navota, a Chicago Metropolitan Agency for Planning director who oversees water management work.
“The more you do that, the more you can push a new well into the future, the more you can push a new treatment plant into the future,” Navota said.
As part of its change to Lake Michigan water, Joliet will aim to reduce its lost water — from main breaks to meter inaccuracies — below 10% by 2030. Earlier this month, a Joliet main under the Des Plaines River broke and leaked an estimated 6 to 10 million gallons, a severe example of the challenges communities face with leaky systems.
In recent years, more than 30% of Joliet’s water was estimated to be lost, with losses totaling more than $3 million annually. In the coming years, the city will undertake an effort to replace all water mains constructed before 1970.
“How do you bring more communities on to the Lake Michigan water supply?” said Joel Brammeier, president and CEO of the Alliance for the Great Lakes. “You conserve that supply as best you can.”