Dear Tom,
How much has the level of Lake Michigan fallen because of our present drought?
—Edward Llput, Prospect Heights
Dear Edward,
Hydrographically, Lakes Michigan and Huron are one lake. Typically, a springtime rise in the level of the lakes occurs with extra spring rainfall and resultant runoff into the lakes, peaking in the summer, followed by a decline in the level in the autumn and winter because of increased evaporation and less precipitation. But so far this year, much drier than normal precipitation has resulted in falling water levels that as still about 18 above average levels. But remember, the level of the lakes depends upon precipitation across the entire lakes’ watershed, not just precipitation here at Chicago. A one inch rise in the Michigan-Huron system equals 790 billion gallons of water.