DULUTH, Minn. (AP) — Rapidly rising water levels in the Great Lakes are damaging shorelines and creating uncertainty for lakeshore residents.

Duluth has dealt with three major storms on Lake Superior in less than two years, with the latest hitting last October. The city’s construction project supervisor, Mike LeBeau, said high water levels are making the storms even more destructive, Minnesota Public Radio News reported . Duluth officials estimate total damage from the three storms at nearly $30 million.

“It’s been hard for the city to catch its breath, frankly,” LeBeau said.

Around the Great Lakes, beaches have disappeared, docks have been submerged and the shoreline is eroding. Lake levels began rising rapidly in 2014. This summer, lakes Erie and Ontario reached their highest levels ever recorded, thanks to months of abnormally wet weather keeping stream flows into the Great Lakes well above average. Lake Superior, meanwhile, has set new monthly records.

The higher lake levels are a boon for the shipping industry, which was complaining about record low water levels only six years ago. Deeper water allows ships to carry more cargo.

Duluth Seaway Port Authority spokesman Jayson Hron cites the lake freighter Edwin H. Gott, which can carry an additional 267 tons of iron ore per extra inch of draft, the distance between the waterline and the deepest point of the ship’s hull.

“That’s something like $26,000 worth of extra ore per inch, so if you multiply that by 2 or 3 inches of water level, and then multiply it by more than 30 trips over the course of a shipping season, it adds up to some significant benefits,” Hron said.

Great Lakes water levels began quickly dropping in the late 1990s, and that downward trend lasted 15 years. Warm lake temperatures led to high evaporation rates, causing the decreased levels, said Drew Gronewold, a University of Michigan environmental science professor and former hydrologist at the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Laboratory.

“There really isn’t a period of below-average water levels in the record for quite that long a time period,” Gronewold said. Great Lakes water data goes back a century.

Gronewold said the quick transition was “one of the most rapid water level increases in history.”

Lauren Fry, a hydrologist with the U.S. Army Corps of Engineers’ Detroit district, said the current spike in water levels was driven by an increase in rain and snowfall over the Great Lakes and the surrounding land that runs off into them.

“Over the past six years, we’ve had above-average water supply more often than not,” Fry said, “so, it’s been an ongoing building of high water levels, culminating this season.”

Increased precipitation, including more extreme rainstorms, is one of the signs of climate change in the Upper Midwest, since the warmer atmosphere holds more moisture, Gronewold said.

But the water level rise also coincided with extremely cold winters, including the “polar vortex” cold snap in 2014, which produced record-breaking ice cover on the Great Lakes. In turn, that slowed evaporation rates because the thick ice took much longer to melt.

Gronewold said it’s a tug of war between increased precipitation, with more severe events, and the likelihood of evaporation increasing again.

“The oscillation between those two extremes is what could be leading to more future rapid oscillations between extreme water levels, as well,” he said.

The rapid transitions between high and low water levels puts people who live and work along the Great Lakes in a tough spot compared with people living on ocean coasts who only have to prepare for sea levels going up, Gronewold said.

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Information from: Minnesota Public Radio News, http://www.mprnews.org

Copyright 2019 The Associated Press.