The Dynamic Great Lakes
Water levels in the Great Lakes have always been highly variable. They fluctuate over many time frames – from hours to millennia – in response to wind, storms, precipitation and evaporation from the lakes’ surfaces and runoff from tributaries.
Seasonal variation occurs every year as the lakes rise an average of 12-18 inches from winter to early summer. Long-term fluctuations lasting many years, decades or longer are visible in the historical record. Each Great Lake is unique in how it responds to the factors that influence lake levels: it depends on the size and composition of the lake’s watershed, total volume of the lake basin and other characteristics. The lakes also influence each other’s levels, as they are all interconnected.
One common concern when looking at varying lake levels is how climate change could potentially affect them. Since we cannot predict high or low levels in relation to climate with a high level of certainty, communities should plan for ongoing variability. Michigan Sea Grant created the following fact sheets to help address what residents, communities and leaders should know in the face of changing lake levels – with or without the impacts of climate change.
Fluctuating Lake Levels
With more than 3,000 miles of Great Lakes shoreline, lake levels have a huge impact on Michigan’s coastal communities and economies. Lake levels affect coastal properties and infrastructure, plant and wildlife habitat, shipping, recreation and manufacturing.
When levels fluctuate much above or below the long-term average, the impacts can be significant, especially in highly developed areas where infrastructure was not designed to withstand changing levels. How will climate change affect the lake levels? Will there be significant changes?
The bad news: we don’t know exactly how things will change.
The good news: we don’t need to know exactly.
See: Preparing for Variable Lake Levels: The Dynamic Great Lakes (PDF)
Plan for Highs and Lows
In Michigan, the weather changes frequently and sometimes drastically. Water levels also naturally fluctuate daily, seasonally and over decades. The changing climate adds yet another layer of variability.
In recent decades, we have seen more severe and frequent extreme events like major storms and heat waves (Michigan summers 2006 and 2010). Scientists expect these trends to continue. Whether or not they do, climate and lake levels will continue to change. For instance, lake levels are low now, but they will eventually rise again. Building coastal infrastructure expecting low levels to persist indefinitely will leave us unprepared for when they rise again. To prepare for variability means to prepare for a range of outcomes.
See: Preparing for Extremes: The Dynamic Great Lakes (PDF)
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Ups and Downs
Whether future climate matches the predictions of scientists, consider this: it doesn’t matter. The reality is that weather, climate and lake levels will continue to be variable. Instead of reacting to the highs and lows in temperature, precipitation and lake levels, coastal communities should expect and prepare for these ups and downs.
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