WEEKLY WATER NEWS

DATASTREME WES WEEK THREE: 18-22 September 2006


Water in the News



Concept of the Week: Great Lakes Water Levels

In recent years, Great Lakes water levels declined significantly to near historic lows. In late 2000, Lakes Superior, Michigan, Huron, and Erie experienced their lowest water levels in 35 years with serious implications for lake-based activities. Over the past year or so, however, changes in weather conditions in the Great Lakes watershed appear to have somewhat reversed the decline in water levels, but they still remain below long-term averages.

From 1997 to 2001, Lakes Michigan and Huron dropped by 104 cm (40.8 in.) and Lake Erie dropped by 96 cm (37.6 in.), encompassing the greatest three-year drop in lake levels since continuous records began in 1860. This dramatic decline in lake level was due to a combination of weather conditions in the Great Lakes watershed. Rainfall, snowfall, and air temperature during winter and spring govern water levels of the Great Lakes in spring and summer. Spring melting of the winter snow pack in the watershed is an important contributing factor as is air temperature that ultimately governs evaporation rates. During 1997, 1998, 1999, and 2000, lower than normal precipitation and higher than normal temperatures reduced the winter snow pack, decreased discharge on rivers flowing into the lakes, and accelerated lake evaporation. Although input of water into the Great Lakes was above the long-term average in Fall 2001, lake levels remained well below average because of less than the usual snow melt in the Spring of 2001 and less than normal winter ice-cover in 2001-02. (More open water translates into greater winter evaporation.)

Great Lakes water levels showed signs of recovery during 2002, but in early 2003, all the lakes were lower than the long-term average for that time of year. A cool wet summer in the eastern Lakes region, but dry summer weather across the west meant that lake levels for the upper lakes continued to remain below average, while the lower lakes had levels that returned to near average. The cool summer of 2004 was very similar to 2003, with below average precipitation across the western Lakes and above average rainfall over the eastern Lakes. By mid September 2004, Lakes Erie and Ontario had water levels that were above the long-term monthly average. However, following a dry spring and summer of 2005, lake levels of the upper (or western) Lakes fell below long-term averages and remained below average into 2006. Continued drought and unseasonably warm weather across sections of the Upper Midwest during the summer of 2006 caused the level of Lake Superior to fall to approximately 26 cm ( 10 in) below the long-term average by September 2006 and the levels of one year ago. The levels of Lakes Michigan and Huron were about 54 cm (21 in) below the long-term average at the start of September 2006. (The Straits of Mackinac that link Lakes Michigan and Huron are so wide and deep that the levels of these two lakes are essentially the same.) On the other hand, the lower lakes had received sufficient precipitation that helped bring levels to above long-term average levels by the end of Summer 2006. Levels on Lakes Erie and Ontario were slightly above the above long-term averages, with the level of Erie being 6 cm (2.4 in) above the long-term average and on Ontario 4 cm (1.5 in) above.

Low lake levels adversely impact commercial navigation, marinas, recreational boaters, and electric power facilities. Shallower than usual water requires expensive and environmentally damaging dredging to keep shipping channels navigable and ports open. Even with more dredging, some channels cannot accommodate the draft of heavily laden freighters. Reduced carrying capacity impedes transport of grain, coal, ore, and other raw materials to processing facilities and markets. In 2000, Lake Carriers transported 5% to 8% less cargo, sending prices higher. If storm winds cause near-shore water levels to fall, marinas, docks, and boat ramps may be temporarily inaccessible. The Great Lakes supply most of the potable water for lakeshore communities and cooling water for coal-fired and nuclear electric power plants located along their shores. A drop in water level may require costly repositioning of intake pipes. On the positive side, lower lake levels translate into broader beaches and wetl and habitats and less shoreline erosion.

For more information on past, current, and anticipated Great Lakes water levels, go to http://www.glerl.noaa.gov/data/now/wlevels/, a web site maintained by the Great Lakes Environmental Research Laboratory (GLERL). Records of Great Lakes water levels constitute one of the longest high quality hydrometeorological data sets in North America, dating back to about 1860. Lake level measurements are collected and archived by NOAA's National Ocean Service.

Concept of the Week: Questions

  1. With rising temperatures, the rate of evaporation of water [(increases)(decreases)].
  2. A trend toward snowier and colder winters and springs is likely to cause levels of the Great Lakes to [(rise)(fall)].

Historical Events


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Prepared by AMS WES Central Staff and Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2006, The American Meteorological Society.