The drop-off began in the late 1990s
Four of the giant lakes — Superior, Huron, Michigan and Erie — were above their average monthly levels in November, while Lake Ontario was slightly below. In September, all five were simultaneously above average for the first time since the drop-off began in the late 1990s. A newly released forecast predicts little change over the next six months.
It’s a dramatic and remarkably swift rebound from January 2013, when Michigan and Huron — which are linked and have the same level — reached their lowest point since the government began keeping records nearly a century earlier. The others were mired in a prolonged slump, although Ontario was better off because hydropower dams help regulate its ups and downs.
“On Superior, Michigan and Huron, we haven’t seen two-year water level increases of this magnitude” in recorded history, said Keith Kompoltowicz, a hydrologist with the U.S. Army Corps of Engineers district office in Detroit.
The wild swing illustrates the uncertainty that may confront the eight states and two Canadian provinces where the lakes are an economic pillar and source of drinking water for more than 30 million people. Climate models suggest global warming may fuel increasingly severe storms and droughts, along with temperature extremes that can influence evaporation rates.
“That’s certainly a risk going forward,” said Jim Noel of the NOAA Ohio River weather forecasting centre. “When we have a warming climate system, the bottom line is that it yields greater year-to-year variability.”