Water Levels of the Great Lakes MENT of C Water Levels Have Fluctuated Throughout the History of 2011 Update the Great Lakes

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U E .S C .D R E E PA M RT OM Water Levels of the Great Lakes MENT OF C Water levels have fluctuated throughout the history of 2011 Update 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.

The Hydrologic Cycle

Precipitation Low lake levels at Old Mission Point lighthouse, Grand Traverse Bay, Lake Michigan in July 2010. Photo: NOAA.

Runoff Transpiration Percolation Who is Affected by Changing Lake Levels? Evaporation Groundwater Table Record high water levels of 1986 affected many residents and River businesses located along the rivers that provide water to the Great Lakes lakes and along the shoreline of the lakes themselves. In 1986, the Tittabawassee River basin, which eventually empties into Lake Huron, endured an extraordinary amount of rainfall in a short period of time (up to 14 inches in 12 hours) resulting in Why Do Lake Levels Fluctuate? flooding. Heavy river flooding not only causes property damage Great Lakes water levels respond to changes in water supplies, to businesses and residents, but water that runs off the land carries including precipitation, runoff from tributaries, and evaporation pesticides and nutrients with it. Water quality of the runoff water from the lakes’ surfaces. The primary driving forces are may affect the riverine and lakeshore ecosystems. precipitation and evaporation. Lower precipitation leads to lower runoff from the basin, and higher evaporation draws water Water levels during the recent low episode (1997–2007) affected from the lakes causing levels to decline. many interests, including commercial navigation, recreational boating, marinas, beaches, fishing, cottage and homeowners, and the aquatic ecosystem. For example, in the year 2000 the What are the Present Conditions? Lake Carriers that transport iron ore, coal, grain, and other raw Water levels in Superior, Michigan-Huron, and Erie dropped cargoes were forced into “light- sharply from 1997-1999 and have remained at relatively low loading,” carrying 5-8 percent levels since that sudden decline. Following slight increases less goods, sending prices in 2008 and 2009, levels in all these lakes dropped again higher. Additionally, marinas in 2010. Levels as of February 2011 are below those of spent millions to dredge boat February 2010; Superior is approximately 0.3 meters lower, slips, channels, and harbors Michigan-Huron approximately 0.5 meters lower, and Erie along Great Lakes coasts. approximately 0.2 meters lower. Lake Ontario is tightly Nuclear and hydropower regulated and remains at levels similar to those of 2010. plants that use Great Lakes water for cooling and energy The four graphs on the next page show yearly-averaged water generation, respectively, either levels; they are updated through 2010. spent millions of dollars to relocate their cooling pipes or For more information: didn’t generate enough power High lake levels on Lake Michigan in 1986 www.glerl.noaa.gov [email protected] to meet customers demands. caused severe erosion. Photo: NOAA NOAA Great Lakes Environmental Research Laboratory 184.5 Lake Superior 184.0 Lake Superior 605 603 604 184.0 183.5 602

, IGLD85) 603 , IGLD85) 601 eet, IGLD85)

183.5 602 eet, IGLD85)

l (f 183.0 l (f

ve 600 ve l (meters ve l (meters ve 601 Observed 95%

183.0 80% 599 600 182.5 ter le Wa ter le Wa ter le Wa 50% ter le Wa

Mean long−term water level (1860−2010) Predicted 598 599 20% 182.5 Mean annual water level 5% 182.0 597 1860 1890 1920 1950 1980 2010 AS ON DJ FM AM JJ AS ON DJ FM AM JJ AS ON 2009 2010 2011

177.5 Lake Michigan−Huron 177.0 582 Lake Michigan−Huron 580 581 177.0 176.5 579 , IGLD85) 580 , IGLD85) eet, IGLD85)

578 176.5 579 176.0 eet, IGLD85) l (f ve 577 el (f l (meters ve el (meters

578 Observed ev 176.0 95% 80% 576

577 175.5 ter l Wa ter le Wa ter l ev Wa ter le Wa Mean long−term water level (1860−2010) 50% 576 Predicted 575 175.5 Mean annual water level 20%

5% 175.0 574 1860 1890 1920 1950 1980 2010 AS ON DJ FM AM JJ AS ON DJ FM AM JJ AS ON 2009 2010 2011 What is IGLD85? Great Lakes water levels are measured from an elevation reference point referred to as the International Great Lakes Datum (1985). This datum is referenced to sea level as measured at What is the Outlook Rimouski, Quebec, near the mouth of the St. Lawrence River. Every 25-30 years, the IGLD is changed to account for crustal movement–the ‘bouncing back’ of the earth’s crust from the weight of the glaciers. for 2011?

175.0 Lake Erie 574 175.0 Lake Erie 574

573 573 174.5 174.5

, IGLD85) 572 572 , IGLD85) eet, IGLD85) 571

174.0 eet, IGLD85) 174.0 571 l (f l (f ve 570 ve l (meters ve l (meters ve Observed 570 95% 173.5 569 80% 173.5 ter le Wa ter le Wa ter le Wa 569 50% ter le Wa

Mean long−term water level (1860−2010) 568 Predicted 20% 173.0 Mean annual water level 568 173.0 5% 1860 1890 1920 1950 1980 2010 AS ON DJ FM AM JJ AS ON DJ FM AM JJ AS ON 75.5 Lake Ontario 2009 2010 2011 247 NOAA Great Lakes Environmental Research Laboratory’s Advanced Hydrologic Prediction System (AHPS) produces 75.0 246

, IGLD85) probabilistic lake level forecasts 1-10 months into the future 245 based on present conditions combined with climatic outlooks eet, IGLD85) 74.5 244 generated by NOAA and Environment Canada. These l (f ve l (meters ve forecasts are updated regularly to reflect changing conditions 243 74.0 and outlooks. The outlook as of February 2011 indicates that

242 ter le Wa ter le Wa water levels in Lakes Michigan-Huron and Erie will likely be Mean long−term water level (1900−2010) lower than those of 2010 for the next 6 months, while Superior 73.5 Mean annual water level 241 will likely experience levels slightly lower than or similar to 1860 1890 1920 1950 1980 2010 those of 2010 into the early summer.