NOAA 2000-517
Contact: Jana Goldman


The Great Lakes, which were expected to reach record low levels this summer because of mild winters and lack of precipitation, have not dropped as drastically because of a very simple reason -- rain, say NOAA scientists.

"It rained," said Frank Quinn, senior research hydrologist at NOAA's Great Lakes Environmental Research Lab in Ann Arbor, Michigan. "Precipitation, combined with the cool summer temperatures we have been having, has increased the lakes' seasonal rise."

Lake levels have dropped precipitously over the past three years, a trend which was to have continued this summer. But while they have not plunged further, Quinn says lake levels are still within their expected forecast range.

"They are just on the high end instead of the low end," he says. "Even if people have slightly less trouble pulling their boats from the water this fall, the low levels will probably continue to negatively affect commercial shipping and hydropower production."

Lakes Michigan, Huron, Superior, Erie and Ontario make up the Great Lakes system. Combined, they are the largest fresh water body in the world. They serve as a major transportation and recreation area for portions of eight states and the province of Ontario.

At the end of July, all the lakes were below last year's levels, but were showing signs of rising because of the above average rainfall in May and June, according to NOAA water level plots.

"The rain helped, but we are going to need even more to undo the effects of the past three years," Quinn said.

The lakes began losing water three years ago because of a combination of low precipitation, higher evaporation and higher air temperatures. Snowpack, which replenishes the lakes as it melts, has been minimal during the past few years and was in the lake system by early March.

Quinn also suggests that a new approach to forecasting the lake levels may be needed.

"Over the long term, we are no more accurate in predicting lake levels than we are in predicting the weather," he said. "The past few months are just a recent example. Instead of expecting to predict the precise rise or fall of the lakes, it is more reasonable to present a range of future water levels. Then we could rate how likely it is for any of those possibilities to occur."

Quinn suggests something similar to weather forecasts that say "there's a 30 percent chance of rain tomorrow."

"That still means there's a 70 percent chance that it won't rain. Similarly, if we say there's a 30 percent chance that the lakes will rise during the summer, people will know that there is a likelihood that they will fall, or remain unchanged," he said. "Such a system would allow us to take many more climate variables into account when we talk
about the future."