The recent "polar vortex" that swept the U.S. could cause the Great Lakes' water levels to rise this year.
New research suggests not only does ice cover affect lake evaporation, but it is affected by autumn evaporation rates itself, a University of Michigan news release reported.
High autumn evaporation rates could "offset water-level gains" that are associated with winter ice cover, which could make it difficult to predict what Great Lake water levels will look like in the future. The lakes' water levels declined during the 1990s and early 2000s, but had a surprising rebound in 2013.
The study is the first to look at "evaporation across the Great Lakes." The team showed that in order for thick ice to cover the Great Lakes it was required that significant heat loss occurred during the autumn and early winter. Evaporation is a primary source of that heat loss.
"Extensive ice cover is actually an indicator of high evaporation rates prior to a high-ice winter," Peter Blanken of the University of Colorado said according to the news release.
The team worked to understand how temperature variations affect the Great Lakes' water levels.
"No two years are alike when it comes to Great Lakes evaporation, ice cover and water temperatures, but the recent documented changes in the lakes' water balance are aligned with predictions associated with climate change," Christopher Spence of Environment Canada said in the news release. "That's why these new measurements over each of the Great Lakes have been so valuable to better understand these seasonal, inter-annual and long-term variations."
John Lenters, the study's lead investigator and a senior scientist at Ann Arbor-based LimnoTech, noticed that evaporation rates during freezing December 2013 evaporation rates were 60 percent higher than they were in December 2011.
"Most people would find this counterintuitive," Lenters said. "Why would a lake evaporate more rapidly during a colder month? The answer, it turns out, lies within the lake itself."
The high evaporation rate during these chill months is most likely thanks to the fact that the water can be 30 to 40 degrees higher than the above air, causing a dramatic moisture difference and spurring evaporation.
The freezing polar vortex most likely caused high winter evaporation rates and could cause the ice cover to last for longer than usual. This means the water would stay colder for longer and delay the start of evaporation season.
"Together with high spring runoff from this winter's heavy lake-effect snowfall, it would be reasonable to expect a healthy rise in Great Lakes water levels this year," Lenters said.
Studying these lake changes is important for a number of industries.
"Understanding how lake levels are changing is very important to our region," Thomas Dietz, a professor of environmental science and policy at Michigan State, said. "This affects shipping, recreation and infrastructure on the lake shore."
