Traverse City Record-Eagle

Michigan

January 22, 2014

Report: Water levels complex

TRAVERSE CITY — Rising and falling water levels in the Great Lakes are influenced by evaporation, rain and snowfall in ways that aren’t fully understood and are becoming less predictable as the climate warms, according to scientific reports made public Tuesday.

This winter’s bitterly cold weather is forming ice on areas of the lakes that will reduce evaporation by blocking water vapor from rising into the atmosphere and keeping water temperatures cool well into summer. That should help water levels continue a rebound that began in 2013 following an unusually long slump across most of the lakes dating from the late 1990s, said John Lenters, senior scientist at LimnoTech, an environmental consulting firm in Ann Arbor.

But recent studies show that evaporation and ice cover regulate lake levels in more complex ways than previously believed, according to a new paper published by the Great Lakes Integrated Sciences and Assessments Center, a joint U.S.-Canadian research team led by Lenters. The team is developing a network to measure evaporation rates continuously, providing data that will improve water level forecasts — a helpful tool for the cargo shipping and tourism industries and others whose livelihoods are affected by the inland seas’ ups and downs.

Meanwhile, another paper being released this week says the Great Lakes have ebbed and flowed on a fairly consistent 10-year cycle for much of the past century, although the steep decline that began in 1998 suggests the pattern may have been broken. That study, led by Carl Watras of the Wisconsin Department of Natural Resources, says the fluctuations have been influenced by atmospheric trends hatched as far away as the northern Pacific Ocean.

Taken together, the studies confirm that climate is by far the biggest player in determining water levels, Watras said. Human actions make little difference, despite noisy debates over whether structures should be built to regulate flows between lakes or whether communities outside the watershed should be permitted to draw from them, he said.

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