The polar vortex came with a silver lining: Water levels are up on the Great Lakes this summer, providing welcome news to boaters, beach-goers and cottagers who have become increasingly nervous about changing shorelines.
The good news is muted, though, by the fact that this year's higher levels come after a period of record lows. Numerous studies have attempted to explain the longer-term declines and whether they are part of a cycle of long-term fluctuations or signal permanently lowered levels. Dredging of the links between lakes, natural cycles and increased evaporation due to climate change have all been listed by experts as factors.
Reached by phone on his boat near Midland, Ont., David Sweetnam says water levels in his region are about nine inches above last year. But the executive director of Georgian Bay Forever, an environmental advocacy group, said those with deep roots in cottage country know the water is still below the historical average and long-term trends remain a concern. He expects this year will be a "blip" caused by the unusually cold winter.
"There's kind of a wisdom up here that the water level fluctuates annually, but that in general it's lower than it has been," he said.
Recent water level readings show Lake Michigan and Lake Huron (which includes Georgian Bay) are higher than last year but 12.7 centimetres below the long-term monthly average covering the years 1918 to 2013. However, Lake Erie is 10.2 cm above average, Lake Ontario is 12.7 cm above average and Lake Superior is 17.8 cm above average.
The link between this year's generally higher water levels and the recent polar vortex was outlined in a column posted earlier this year by the International Joint Commission (IJC), the organization that studies the Great Lakes for the governments of Canada and the United States.
Jim Bruce, a former senior official with Environment Canada and former director of the Canadian Centre for Inland Waters, wrote that two factors would contribute to higher water levels this year. The higher-than-normal ice cover on the Great Lakes over the winter reduced evaporation, while the larger snow pack would also boost water levels.
"This unusual set of winter conditions will only break temporarily the long-term climate-warming trend affecting Great Lakes levels and water quality," he wrote.
Fluctuating water levels over the years go beyond environmental factors. The St. Clair River, which flows out of Lake Huron, has been dredged numerous times to accommodate shipping. But digging a deeper river ultimately drains more water from Lake Huron and Lake Michigan, sending it downstream to Lake Erie.
The Great Lakes hold nearly 20 per cent of the world's fresh surface water.
A June 26 report published by Ontario's Mowat Centre, a public policy think tank, predicted significant economic damage if the lower water trends continue. The report said a continuing decline in water levels would hurt the regional boating and fishing economies, as well as commercial shipping, waterfront property values and hydroelectric generation.
The study projected the economy in the Great Lakes and St. Lawrence River basin could take an $18.8-billion hit by 2050 if those trends continue.
That report did note the recent higher water recordings but said it was unclear if the rebound marked an end to a trend or was a statistical outlier.
In January, the journal Geophysical Research Letters published a study by University of Wisconsin researcher Carl Watras that found water levels rise and fall on a roughly 10-year cycle in Lake Michigan and Lake Huron. However, the research, which looked at 70 years of data, found a break in the pattern as water levels trended downward since 1998.
"The last two decades have been kind of exceptional," Mr. Watras told livescience.com earlier this year.