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Interview with Dr. Frank Quinn

3 | The changing lake levels

Why have the lake levels been so low during the past couple of years?
The Great Lakes are in a very unusual situation right now. Lake Superior's water levels are the lowest they've been since 1925; lakes Michigan and Huron are the lowest they've been since 1965.

The main cause for the current low lake levels is lack of snow precipitation, mainly in the northern part of the basin. The region has also experienced warmer temperatures than it usually does. Temperatures in the Great Lakes basin two years ago were the warmest ever recorded. When the temperatures are high, plants require more water; so plants are using more precipitation and groundwater than usual, decreasing the amount that reaches the lakes.

Listen!  Evaporation: Why the Great Lakes are unique (49 seconds)
Also, there has been less ice on the lakes during the winter because of the warm temperatures, which leads to more evaporation. In smaller lakes, the highest evaporation rates occur in the summer. But the Great Lakes hold large amounts of heat because of their size; therefore, the highest evaporation rates occur in the fall and early winter on the Great Lakes. When the cold and dry Canadian air comes over the lakes, that air is heated, and heated air absorbs more moisture. So as air comes over the Great Lakes, the air literally sucks up the water. Much of that water is dumped back on the land once it cools off, which is known as lake-effect snows.

Click to see larger image. It's interesting to hear people's reactions to the recent low lake levels. Up until a couple of years ago, the basin had seen about 30 years of high lake levels. Many people don't remember or weren't around for the last low lake level period, which was during the 1960's. Right now, people are seeing docks that lead to nowhere because the shoreline has retreated and they're seeing large beaches and rocky lake bottoms. It's an interesting time for residents and researchers alike to be studying the lakes.

Also see TEACH's module, Water Levels on the Great Lakes.

Graphic: Low lake levels on Lake Michigan.

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