Lake Michigan and Lake Huron hit all-time low water levels

During January 2013, water levels on Lake Michigan and Lake Huron fell to their all-time lowest values since record keeping began in 1918, said the U.S. Army Corps of Engineers on Tuesday. The two lakes (which are connected and are hydrologically the same lake) fell to a water level of 576.02'. This is 0.4" below the previous record low of 576.05' set in March 1964. The lakes have dropped 17 inches since January 2012, and are now 29 inches below their long-term average. Lake Superior is about 9" above its all-time low water level, and Lakes Erie and Ontario are just 6" below average (26 - 27" above their all-time lows), so these lakes will not set new low water records in 2013. The latest forecast calls for Lake Superior to drop 2 inches during February, Lake Michigan and Huron to drop 1 inch, Lake Erie to rise 2 inches, and Lake Ontario remain near its current level.


Figure 1. Low water levels at Old Mission Point Lighthouse at Grand Traverse Bay, Lake Michigan, during July 2000. Image credit: NOAA/GLERL.


Why the record lows?
The record-low water levels on Lake Michigan and Lake Huron are due, in part, to dredging operations in their outflow channel, the St. Clair River. The dredging, which stopped in the 1960s, is blamed for a long-term 10 - 16" decrease in water levels. The record low water levels on Lake Michigan and Lake Huron in January occurred despite the fact that precipitation over their watershed was 61% above average during the month. However, precipitation over the past 12 months was only 91% of average, and runoff into the lakes depends upon precipitation over longer than a 1-month period. Furthermore, evaporation over these lakes was much higher than average during January, making the net water supplied to the lakes (runoff into the lakes, plus precipitation over the lakes, minus evaporation from the lakes) only 63% of average. What caused the increased evaporation? Well, very warm water temperatures, for one. According to NOAA's Great Lakes Environmental Research Laboratory (GLERL), water temperatures over Lake Michigan are currently about 2.5°F above average, and are about 1°F above average over Lake Huron. These warm water temperatures are the lingering effects of the extraordinary warmth of 2012, which was the warmest year on record over much of the Great Lakes region. Also increasing the evaporation from the lakes during January was the presence of less ice cover than average, which exposed more open water to the air.


Figure 2. The water level on Lake Huron and Lake Michigan measured during 2012 - 2013 (red line) hit an all-time low during January 2013, beating the previous record set in March 1964. The predicted water levels for February - March call for record lows both months. Image credit: Army Corps of Engineers.

Ice cover declining, water temperatures warming, and precipitation increasing in recent decades
The long-term future of Great Lakes water levels is cloudy, since climate change is expected to bring competing effects. A 2011 paper by scientists at NOAA Great Lakes Environemental Research Laboratory found that lake levels could rise or fall, depending upon the climate change scenario used. On the one hand, precipitation has increased by 12% over Michigan during the past century, and is expected to increase even more in the coming decades. This would tend to increase lake levels. However, lake water temperatures are predicted to increase and ice cover decrease, which would heighten evaporation rates. This would tend to lower lake levels. Ice cover on North America's Great Lakes--Superior, Michigan, Huron, Ontario, and Erie--has declined 71% since 1973, according to a 2012 study published in the Journal of Climate by researchers at NOAA's Great Lakes Environmental Research Laboratory. The loss of ice is due to warming of the lake waters, which could be due to a combination of global warming and natural cycles, the researchers said. Winter air temperatures over the lower Great Lakes increased by about 2.7°F (1.5°C) from 1973 - 2010, and by 4 - 5°F (2.3 - 2.7°C) over the northern Lakes, including Lake Superior. Lake Superior's summer surface water temperature warmed 4.5°F (2.5°C) over the period 1979 - 2006 (Austin and Colman 2007). During the same period, Lake Michigan warmed by about 3.3°F (1.7°C), Lake Huron by 4.3°F (2.4°C), and Lake Erie (which is shallow and loses and gains heat relatively quickly) showed almost no warming. The Army Corps of Engineers is also considering adding speed bumps to the bottom of the St. Clair River to slow down drainage of Lake Huron, which would act to increase water levels in Lake Huron and Lake Michigan.


Figure 3. Average yearly precipitation over the state of Michigan increased by about 12% per century since 1895, according to NOAA's National Climatic Data Center.

References
Austin, J. A., and S. Colman, 2007, "Lake Superior summer water temperatures are increasing more rapidly than regional air temperatures: A positive ice-albedo feedback," Geophys. Res. Lett., 34, L06604, doi:10.1029/2006GL029021.

Wang, J., X. Bai, H. Hu, A.H. Clites, M.C. Colton, and B.M. Lofgren, 2012, "Temporal and spatial variability of Great Lakes ice cover, 1973-2010," Journal of Climate 25(4):1318-1329 (DOI:10.1175/2011JCLI4066.1)

Jeff Masters