Lake Level Research on the Great Lakes

Lake Level Research on the Great Lakes. Mackinaw City Historical Pathway. , Researchers coming and going from Mackinaw City's marina are discovering that evaporation from the Great Lakes, a key factor in the level of the lakes, is far more complicated than formerly thought. An understanding is important for commerce, policy makers and environmentalists. , , What determines the level of the lakes? In the short term, precipitation and runoff bring water into the lakes. Evaporation and drainage, both natural and man-made, take water out. , , Evaporation is the least understood of all of these and is the focus of studies at two nearby lighthouses, chosen as research sites because they sit in the middle of the lakes, tall and unobstructed. , , Evaporation accounts for 40% of the water lost by the lakes; natural drainage accounts for most of the remaining 60%. , , Lower left box: , Conclusion: , November matters the most , , Just one very cold windy spell in November can result in 1/2 inch of water level drop in all of the Great Lakes. The evaporation takes away water and heat from the lakes and will cause ice to form earlier, cutting off the November, December, January evaporation. As ice then builds, it delays the spring thaw, slowing April and May evaporation. , , The feedback cycle is very complex and requires long-term study. , , Upper right box: , Sophisticated equipment is mounted on White Shoal and Spectacle Reef lighthouses to collect the data for Lake Michigan and Lake Huron. , , Data is collected on wind speed, humidity, ice cover (when little or no evaporation occurs), and temperature differentials between the air and water. , , Lower right box: , Information compliments of: , Dr. Peter D. Blanken, Professor , Department of Geography , University of Colorado at Boulder