Below Average Precipitation and Temperatures Affect Water Levels
By IUGLSJan 17, 2012
Photo by Sharon Mollerus
Water levels on Lake Superior have continued to decline in recent months, amid low precipitation and warmer-than-usual weather.
For the fifth month in a row, water supply to the Lake Superior basin was below average for December, according to the latest data from Environment Canada (EC).
Outflows from Superior to Lakes Michigan-Huron also were below average for December. Still, below average supplies caused levels on Superior to drop by 9 centimeters (3.5 inches), about 2 centimeters more than is average for this time of year.
The levels of Michigan-Huron declined as well during December, by 3 centimeters (1.2 inches). Levels rose by 8 centimeters on Lake Erie, primarily due to above-average supplies received in that basin during the month, EC officials say.
According to the latest calculations from Environment Canada, precipitation to the Great Lakes basin for December was 90% of average.
The levels of all of the Great Lakes remain at or higher than they were a year ago. The latest data from the U.S. Army Corps of Engineers shows Superior’s level is unchanged from this time last year, while Michigan-Huron is 7 inches (17.8 centimeters) higher, and Erie and Ontario are 20 inches and 10 inches higher, respectively.
Still, Superior and Michigan-Huron remain 32-30 centimeters below their long-term averages, based on data from 1918-2010, according to Environment Canada. Above-average levels have been recorded on Lakes Erie and Ontario.
EC officials say the levels of Superior, Michigan-Huron and Erie are expected to decline in January, as is typical for the season. Lake Ontario’s level is expected to rise, as it usually does in January.
According to EC data, the six-month net basin supply (precipitation minus evaporation) has been above average for all the Great Lakes, with the exception of Superior.
A separate U.S. Army Corps of Engineers six-month forecast says wet weather could push water levels up this year, as reported by The Detroit News. But those increases could be depleted by evaporation due to warmer-than-normal weather.
Lakes Superior and Michigan-Huron were each 12 inches below average for December, when comparing monthly mean lake levels to long-term averages, Corps officials say. Lakes Erie and Ontario were at above-average levels in that comparison, by 17 and 4 inches, respectively.