June 21, 2021

Water is Falling (Lake & Sky Edition)

Recall how not too long ago—last summer, in fact—the level of water in Lake Michigan was flirting with its all-time high, walking on the sidewalk at Burnham Harbor meant your feet were underwater, once ample beaches were reduced to slivers of sand, and storms caused significant erosion along the lake shore?

Since last July, the water level in Lake Michigan has dropped 20 inches and the US Army Corps of Engineers predicts Lake Michigan will drop another foot by December. You’ll want to know that 20 inches of water across the expanse of Lake Michigan is 8.1 trillion gallons. Because Lake Michigan and Lake Huron are considered one system—they are connected to each other at the Straits of Mackinac—the lakes combined have 16.8 trillion gallons of water less than a year ago. Oooof. Where did all that water go?

Fig1 Spring Levels.jpg

Fig2 Lake Fall.jpg

Water fills the Great Lakes in two major ways and departs in another: precipitation, runoff, and evaporation. Looking at the past year, these inputs and output explain why the water level in the lake has been falling.

Beginning with precipitation, Cook County has received 11.9 inches less rainfall in the past year than average. The entire Lake Michigan basin fell short of the average by 5.2 inches. It’s been so dry that the U.S. Drought Monitor classifies much of the Lake Michigan basin as being in a severe drought condition.

Fig3 Soil Moisture.jpg

Since this area had so little rain (until last night, noted below), less new water has been deposited in the form of rain and snow into Lake Michigan. In the meantime, the water that’s already there evaporates into the atmosphere. Especially in the winter months, dry air soaks up water from the lakes. Ice cover can prevent or reduce evaporation by separating the lake’s surface from the thirsty air above. You may remember the cold and heavy snow we received in February, but this winter overall was a mild one. For most of the season, ice cover was below average, allowing more water to escape the lake. When water evaporates from Lake Michigan, it doesn’t just sit in a cloud above the lake’s surface. Instead that water vapor gets pushed around in the atmosphere and falls into other watersheds, mainly east of here.

Did you know that water also evaporates from soil as well as surface water (and skin, for that matter)? When soils are dry, they absorb more water, and less water runs off into Lake Michigan. According to NASA data, the soil throughout the Lake Michigan basin, including here in Illinois, is extremely parched. This means even if we do get storms to alleviate the drought, much of the water will soak into the soil rather than making its way into Lake Michigan.

The Army Corps of Engineers combines these three factors—precipitation, evaporation, and runoff—with the natural flow of water out of Lake Michigan-Huron into the St. Clair River. In an average year, the spring rains and snowmelt raise Lake Michigan more than 10 inches between February and June. Not so this past year: during eight of the last 12 months, Lake Michigan was losing water. Every day in January, upwards of 100 billion gallons more water was leaving Lake Michigan than was entering it.

Periods of low rainfall also create challenges at sewage treatment plants. Water needs to be flowing through the plants to push the treatment processes along and to provide a favorable environment for the good bacteria that gobble up nutrients and other contaminants. When there’s low flow—from a global pandemic keeping water-using industries and restaurants closed, a drought, or both—these treatment processes slow down and the bacteria require careful attention.

Then Came the Storm

Like me, those of you in northeastern Illinois and nearby may have spent the early hours of Monday morning sheltering in a windowless room to wait out the storm, which dropped more than 2 inches of rain on some parts of Cook County in a span of hours. The weather station at O’Hare Airport reported 1.7 inches of rain in just an hour. Remarkably, no combined sewer overflows were reported despite all this rain. That’s worth repeating: despite significant rainfall of 1–2 inches in parts of Cook County, there were no combined sewer overflows discharging sewage and contaminated water into the Chicago waterways. The system of tunnels and reservoirs is working!

Another inch of rain, or more, is expected this weekend. These sporadic, intense rains are welcome relief but likely will not lift us out of this current drought. That is, we must get used to seeing patterns that are not obvious; just because we can see water does not mean we are immune from drought any more than the snow and polar vortexes mean we are not experiencing a warmer climate. These are the facades we encounter with our current climate crisis. We are on our way to a new normal.

Solstice Celebration?

Some faithful readers have asked, “What about your annual summer solstice celebration?” For 15 years running, until June 2020, I had hosted an event to celebrate the summer solstice and raise money to support my campaigns and ongoing work (such as this newsletter). Then came the pandemic and we cancelled the 2020 event and weren’t sure we could gather safely in groups in time to plan a 2021 event. Happily, we are emerging, sometimes on tiptoe, from our shelters. Happy Summer Y’all! 

My team and I are conferring and may endeavor to plan a gathering later this summer or in early fall. In the meantime, please know that your support of my work is most welcome!