Undercurrents: beneath the obvious

March 13, 2007

Great Lakes levels plunge in February

Filed under: Great Lakes News,Lake Levels — nemo @ 8:16 pm

The Muskegon Chronicle carries this update on lake levels in February:

Water levels in Lake Michigan and Lake Huron dropped six times faster than average in February, a startling plunge that one expert attributed to the region’s increasingly bizarre winter weather.

The lakes’ water level dropped three inches in February, according to the latest data from the U.S. Army Corps of Engineers. On average, the water level in lakes Michigan and Huron — which are technically one body of water — drops a half-inch in February, according to data the Corps of Engineers has tracked over the past century.

The lakes are currently 16 inches below their long-term average for early March, according to federal data. Great Lakes water levels typically fall in the winter and rise in the spring, after the snow melts.

Water levels have dropped nearly four feet in Lake Michigan since 1998. That change is significant because lower lake levels drive up the cost of shipping and can make recreational boating more dangerous.

For each one-inch drop in Great Lakes water levels, freighters have to reduce their cargo by 50 to 270 tons to avoid running aground in shallow channels and harbors, said Glen Nekvasil, a spokesman for the Cleveland-based Lake Carriers Association.

Lake Superior’s water level fell four inches in February, twice the average decline in winter. The lake is close to its lowest water level ever, recorded in 1926, said Carl Woodruff, a hydraulic engineer at the Corps’ Detroit office.

Several factors contribute to lower lake levels:

  • Above-average summer water temperatures kept the lake warmer during the following winters.
  • Milder winters reduced ice cover on the lakes, which increased water evaporation during the winter.
  • Warm lake water is more susceptible to evaporation during the cold winter months.
  • When dry, cold air flows over the lake in the winter, it draws more moisture out of the relatively warm water and triggers larger lake-effect snow showers.
  • When snow melts before the ground thaws, most of the water evaporates and is lost. Under normal conditions, snow melts slowly in late March and April, is absorbed into the ground and slowly flows back into the lake.
  • Drought conditions in northern Wisconsin and the western half of the Lake Superior drainage basin also have contributed to lower lake levels in the last couple of years, according to Corps of Engineers officials.

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