Talk about a speedy recovery. Three of the five Great Lakes recovered their water levels at record or near-record pace, with Lake Superior gaining 2.3 feet from January 2013 through November of this year, and Lakes Michigan and Huron increasing by 3.2 feet in that same period. That’s the fastest ever for Superior and the second fastest (after the 1950-51 season) for Huron and Michigan.

“The levels of the Great Lakes go up and down all the time, that’s a given,” Anne Clites, a scientist with the National Oceanic and Atmospheric Adminitration’s Great Lakes Environmental Research Laboratory, told weather.com. “They go up for a few years, they go down for a few years. They have not, in the 155 years we have records for, stayed that far below their long-term mean. That was kind of an unusual event. That’s why we’d like to look at more about what’s causing it.”

NOAA researchers have some educated guesses. Based on the data they’ve so far amassed, some combination of unusual precipitation and evaporation patterns seem to be the cause, Clites says. Precipitation in the region during the past two years has been, on average, about 10 percent above average. And the ice cover that stuck around from several harsh winters prevented some of the usual evaporation from occurring.

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“Evaporation [of the Great Lakes] is highest in the fall, and the water loss drives the water levels down. That didn’t really happen very much the last two falls,” Clites says. “Lake Michigan and Huron in general peak in July or August. That’s the highest point of the year. This year … they kept rising right through the fall. That’s really unusual.”

The scientists plan to look at more actual precipitation and evaporation data, as well as models, from both the United States and Canada to better understand the fast increase.

In general, having the lakes return to earlier levels (or slightly higher) is a good thing, Clites says. Boaters can reach marinas previously cut off because of lack of water and the commercial shipping industry is “feeling much happier,” she adds. “The fact that the upper lakes were low for that period of time is also unusual.”

Whether climate change plays a role in this ebb and flow isn’t clear. Clites says there’s hard evidence that water in the Great Lakes has been getting increasingly warmer. What NOAA scientists don’t know, however, is how that factor affects evaporation. More answers are sure to come as the scientists sort through the data. But as Clites says, understanding this is a work in progress.

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