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After more than a decade of falling water levels, Lake Superior is on the upswing.

For 14 years, water levels in Lake Superior, the world's largest freshwater lake, have remained below their long-term average, the longest stretch of below-average levels in recorded history. The big lake reached its all-time low in 2007.

This past spring, Lake Superior rose by 20 inches, fueled by massive runoff from big rain and snowstorms, said Keith Kompoltowicz, watershed hydrology branch chief for the U.S. Army Corps of Engineers.

That was one of the largest seasonal rises ever recorded since measurements began in 1918. Typically the lake rises only about a foot when the snow melts.

In October, Lake Superior's water level reached more than 601 feet, only two inches shy of its historical average and about 11 inches above its levels of a year ago.

Kompoltowicz said a new forecast projects the lake to remain about two to three inches below its long-term average, unless there's another wet winter. Already this month, precipitation is running about a third above normal in the Lake Superior basin, he said.

"With very wet conditions over the next several months, Lake Superior could meet or exceed its long-term average, which would be the first time in 14 years that that has occurred," Kompoltowicz said.

Water levels in the Great Lakes have historically bobbed up and down by a few inches year to year. But about 15 years ago, water levels across the lakes began to plummet.

Downstream, Lakes Michigan and Huron reached historic lows this past January. But they're also up a foot from a year ago, and even with very dry conditions.

Researchers don't expect the three lakes to approach their historic lows again this year. 

Still, they are predicted to remain well below normal, which has some researchers trying to figure out if that represents a "new normal" for the Great Lakes. Among them is Drew Gronewold, a hydrologist for the National Oceanic and Atmospheric Administration's Great Lakes Environmental Research Laboratory.

Before 1998, changes in rain and snowfall largely affected water levels, he said. But that year there was a major El Nino weather event, or abnormally warm waters in the equatorial Eastern Pacific Ocean. That caused evaporation from the Great Lakes to accelerate dramatically. Since then, water levels have been way down. 

"We don't know if this new regime in which evaporation is extraordinarily high is going to persist, or, if perhaps it's a sort of a shock to the system, or a perturbation that came about because of that 1998 El Nino," Gronewold said. "We simply don't know, we're going to continue to monitor and watch the system to try to understand it better."

A warming climate likely also plays a role. Even before 1998, scientists were observing increases in evaporation that correlated with warmer water temperatures and declining ice cover, something that is "indicative of climate change," Gronewold said.

A couple inches of lost water might not seem like a whole lot along the North Shore of Lake Superior, but it's a huge deal to the shipping industry, said Glen Nekvasil, vice president of the Lake Carriers' Association. 

"This is an industry where inches matter," he said. "Depending on the size of your ship, you lose anywhere from 50 to 270 tons of cargo for each inch of draft that you lose." 

While water levels play a big role, Nekvasil is focusing his efforts on something humans can more directly control -- namely dredging in Great Lakes ports and waterways.

The U.S. House and Senate have both passed bills to help alleviate a dredging backlog in the lakes, and are scheduled to meet in conference committee this week. That could allow ships to take on full cargoes of coal and iron ore again, even if water levels in the Great Lakes never make it back to their historic levels.

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This past spring, Lake Superior rose by 20 inches, fueled by massive runoff from big rain and snowstorms.

Lake Superior water levels on the rise

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