Science

Great Lakes water levels continue to drop: Lake Superior lost 1 trillion gallons last month

Great Lakes water levels continue to drop: Lake Superior lost 1 trillion gallons last month

We are in the seasonal decline of the Great Lakes water levels. Two lakes have fallen so much that they are approaching the average water level.

There is a seasonality to the Great Lakes water levels. If the weather conditions are near normal, Great Lakes water levels are usually at their highest around July. The water levels decline from August through March, and then rise from March to July.

The loss of water in December is therefore to be expected.

Lake Superior declined 2 inches from November 30, 2022 to December 30, 2022. This is a fairly typical amount of water decline for December. It represents what sounds like a bunch of water: one inch of water on Lake Superior equals 550 billion gallons of water. About 1 trillion gallons of water left Lake Superior either through outflow into Lakes Michigan and Huron, or evaporation. In winter, the precipitation amounts decline in the colder air. A loss of water level basically comes down to more water flowing out and evaporating than falling as precipitation. Also, the precipitation is mostly snow in December, which doesn’t make it as water into Lake Superior until the spring snowmelt.

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Water levels of Lake Superior for the past two years and a forecast six months into the future. (Data source: US Army Corps of Engineers)

Lakes Michigan and Huron are one big lake when it comes to determining lake water levels. Lakes Michigan and Huron also declined 2 inches in December. Again, while this is a large number with gallons of water, it is an average water loss for December. Those two lakes now have 1.6 trillion gallons less water than they did on November 30. Much of the world would rejoice to have a trillion gallons of fresh water. It’s a drop in the bucket for us here in Michigan.

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Water levels of Lake Michigan and Lake Huron for the past two years and a forecast six months into the future.

Lake Erie has also lost 2 inches of water in the past 30 days.

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Water levels of Lake Erie for the past two years and a forecast six months into the future.

Lake Ontario water levels can act differently from the rest of the Great Lakes. Lake Ontario’s water level can be regulated somewhat through the St. Lawrence Seaway. As a result, the Lake Ontario water level doesn’t always fall when the other lakes are declining.

In the past 30 days, Lake Ontario has risen 3 inches.

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Water levels of Lake Ontario for the past two years and a forecast six months into the future.

Over the past two years, the water level has been declining a little more than average and the water level has been increasing less than average. This is especially true on Lakes Michigan and Huron. The water level on those two lakes has dropped from record high levels in 2020 to just a few inches above average now. There has been about a 30-inch water decline over the last two years, and that’s after a 4-foot water level increase in the few years leading up to the record water levels.

Lakes Michigan and Huron are only 4 inches above the exact long-term average for December. Lake Superior and Lake Erie are still 6 inches higher than the long-term average. Lake Ontario is one inch below the long-term average.

In a large fluctuating water level regime of the Great Lakes, we could say the lakes are close to average water levels now.

We have moderate to severe drought around the Great Lakes now. If we continue with drier than normal weather, the lake levels will soon slip to below normal levels.

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