Lake Superior’s water level fell 2 inches in February, continuing its seasonal decline. The level of Lake Superior is forecasted to hit its seasonal low in March and remain near last year’s level through August of 2010.
The Great Lakes experienced unusually low levels from 1997- 2007, hitting near record lows in late 2007. This decline eased in 2008, and there was a general increase in levels from 2008- 2009. In February 2010, an ice jam dropped levels in Lake St. Clair; levels have since rebounded with the removal of the jam. As of March 2010, the lakes are at the level, or slightly below, where they were in March 2009.
Great Lakes water levels respond to changes in water supplies, including precipitation, runoff from tributaries, and evaporation from the lakes’ surfaces. The primary driving forces are precipitation and evaporation. Lower precipitation leads to lower runoff from the basin, and higher evaporation draws water from the lakes, causing levels to decline.
Water levels have fluctuated throughout the history of the Great Lakes. Research has indicated that several thousand years ago water levels became so low that the lakes were no longer interconnected as they are currently. More recently, record low levels coincided with the dust bowl years of the 1930s and a severe drought in 1964. The lakes experienced extremely high levels in 1986 and since that time levels have generally been declining. This decline has been a concern because lower water levels are consistent with most global climate change forecasts.
For more information, go to the NOAA Great Lakes Environmental Research Laboratory website at www.glerl.noaa.gov.