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Upper Great Lakes water levels are up. Here's why.

Dec 11, 2014

The Great Lakes go up and down. It's just a fact of life. 

Water levels in Lakes Superior, Michigan and Huron continue to be above their monthly averages for the first time in 16 years.

"... water levels on both Lake Michigan-Huron and Lake Superior have gone through this two-year surge. That is relatively unprecedented." — Drew Gronewold, hydrologist

Drew Gronewold  is a hydrologist at the Great Lakes Environmental Research Laboratory, part of the National Oceanic and Atmospheric Administration.

"In the late 1990s, water levels went down; they went down very fast and stayed low. People got used to it they were asking 'why are they getting low?' "

The Michigan-Huron system hit a record low in January 2013 and it was the lowest monthly average since record-keeping started in 1918. But things started changing: "water levels on both Lake Michigan-Huron and Lake Superior have gone through this two-year surge. That is relatively unprecedented,"  Gronewold says.

The main reason for the increase is increased precipitation.

"There has been more rainfall across the region, particularly over those two lake basins, over the past two years than average."

Did the polar vortex factor in?

Gronewold says that in 2013, there was a big spring rise in water levels followed by a 'below-average decline'. This cycle repeated itself in 2014.

"Keep in mind that in 2013 we weren't dealing with an arctic polar vortex anomaly — that was early 2014. So really what we have here is a pattern across both 2013 and 2014 related more to increases in precipitation, both over the lakes and the precipitation that turns into runoff than really any other factor that we measure." 

Forecast for the future

A seasonal forecast is generated through a joint effort by NOAA, the U.S. Army Corps of Engineers and Environment Canada. Right now, they are predicting a typical seasonal cycle. 

"So not an extreme rise, not an extreme fall, but something following what we typically expect so a little bit more of a decline through the winter and then a typical spring rise," says Gronewold.  "The key point of that being that we would expect water levels to stay above average where they are right now."

Gronewold's not sure whether the levels will hold for all of next year, mainly because of the limitations of forecast prediction. 

"When we get beyond say, one, two, three, four, even five or six months, we start getting to a period where the large scale regional meteorological and climate patterns that drive precipitation and temperature and other factors related to water levels become really hard to predict, " he says.

"One great example is last year's arctic polar vortex anomaly, six months to a year out - nobody saw that necessarily coming, but it had a tremendous impact on the region."