Stories on dropping levels in the Great Lakes have made news recently. We tend to take the lakes for granted as they seem like an inexhaustible resource. However, we are learning this is not the case and we cannot take water for granted.
Recent squabbles among the provinces and states that border the Great Lakes highlight the problems of declining lake levels. While some want to assert their right to export water from the Great Lakes, others fear that further lowering lake levels will affect local water supplies, cripple shipping capacity, reduce recreational value of lakes, and have a bad effect on the ecology of the Great Lakes.
How have we reached a point where some ports are no longer accessible, particularly to larger vessels? Why are the ends of docks metres from the nearest water? Where is all our water going? Is it part of some natural cycle, or will lake levels continue to drop?
The Canada/U.S. Joint Commission, which advises on policies and management for the Great Lakes, is examining some possible reasons for the recent drops. These drops have been most rapid in lakes Huron and Michigan. These two lakes are interconnected and drain through the Saint Clair River to Lake Erie.
Ironically, one suggested reason that larger ships can no longer use some ports may be that the St. Clair has been dredged to allow passage of larger ships. The dredging may be allowing these lakes to drain more efficiently, with water going out faster than the lakes refill.
Another possible explanation is glacial rebound. As glaciers retreat, land that was formerly covered rises, freed of the extreme pressure of the ice. It is a slow, but continuing, process. As glacial retreat has been more recent for northern areas, the current rate of rebound is faster than in southern areas, effectively tipping the lake basin toward the south, and in this case, toward the St. Clair drainage.
A third explanation is that increased evaporation may be responsible. This was suggested by a recent study that brought attention back to reduced lake levels. The researchers found that evaporation rates made a dramatic switch about 30 years ago, from 1 mm/year to 4 mm/year. This is potentially more troubling than other explanations, since increased evaporation may be linked to climate change, as suggested by the authors of the study.
It is likely the declines observed are due to several causes, rather than a single one. And it is true that water levels in the Great Lakes fluctuate, with 30-year cycles in the long term (geologically).
However, the current declines in lake levels that started in the 1990s have lasted longer than expected based on previous cycles.
If these declines continue, and the low levels last for a long time, it would suggest that increased evaporation is having a greater and more persistent role than it has in past cycles.
In the words of the authors from the study, this would provide “good evidence that climate change is rearing its head.”