- Lake levels are primarily driven by precipitation, runoff, and evapotranspiration.
- Following a period of below average water levels from 1998-2013, all of the Great Lakes have experienced higher than average water levels and some record highs in recent years (2015-2020).
- The recent rise in water levels is primarily driven by several years of above average precipitation in the lake basins in the 2010s, as well as several years of high ice cover, including 2014, 2015, 2018, and 2019.
- Prior to these recent highs, long-term water levels in the Great Lakes fell from record highs in the 1980s to below average for over a decade in the 2000s.
- Warmer temperatures and higher evaporation rates were partially responsible for historical declines in lake levels.
- Periods of both high and low water levels are likely to occur in the future, with an overall increase in variability.
A more in-depth analysis of Great Lakes water levels is available here from GLISA in our Sustained Assessment of the Lakes resource.
Both high and low water levels pose challenges in the Great Lakes region. Low levels impact commercial shipping, recreation, and hydropower generation, whereas high levels can cause shoreline erosion, flooding, and property damage. 1 2 3
The past decade has seen substantial variability in water levels of the Great Lakes. As recently as 2013, water levels for most of the lakes were very low: in January 2013, Lake Michigan-Huron set an all-time record low monthly mean water level of 576.02 feet, the lowest value on record, which dates back to 1918. 4 Since 2014 water levels have risen rapidly, and several record highs have been set. In September 2014, water levels for all of the Great Lakes were above their monthly average levels for the first time in 15 years. 5 In the summer of 2019, record high monthly water levels were observed on Lakes Superior, Erie, and Ontario. Widespread flooding has taken place around all five Great Lakes shorelines, and these events are not isolated, as increased precipitation and severe flooding have affected much of central North America. 6
Evaporation, Precipitation, and Lake Levels
Fluctuating water levels in the Great Lakes are primarily influenced by three factors: overlake precipitation, overlake evaporation, and runoff that enters the lakes from surrounding land, tributaries, and rivers.
Precipitation over the lakes adds to the water supply of the basin and increases water levels, while evaporation does the opposite. In the absence of other non-climatic factors, these two processes compete with each other to influence lake levels. Runoff adds to water levels, and is directly affected by factors such as snow cover and soil moisture. Warming temperatures influence these processes and in turn, lake levels. For example, as air and water temperatures have risen, summertime evaporation rates have more than doubled since the 1980s. 7 8 9 Warmer water temperatures also lead to reduced ice cover on the lakes, allowing for evaporation from exposed surface water throughout a longer part of the year. 10
Long-term water levels in the Great Lakes fell during the period from 1998-2013, after record highs were reached in the 1980s, and changes in precipitation and evaporation partially contributed to those declines.11 During 2014, low temperatures were observed across the Midwest throughout the winter, including a period of extreme cold, when a disturbance in the polar vortex shifted Arctic air southward. Lake ice reached near-record maximums and evaporation rates dropped, contributing to the rapid increase in lake levels.12
Future Water Level Projections
Great Lakes water levels are affected by climate variability (e.g., changes in precipitation patterns), climate change, and outflow regulation . As of today, there is not a scientific consensus on the long-term trends of future water levels in the Great Lakes. Many previous modeling studies projected long-term lake level declines into the future. However, recent studies have found that many of these earlier models were overestimating evapotranspiration from the Great Lakes. Newer, more comprehensive models that better account for evapotranspiration project smaller declines or even rises in water levels into the future. Regardless of projected long-term trends, seasonal, annual, and multi-year variability in lake levels is expected to remain large. 13
A 2016 study used updated methods to project water levels in the Great Lakes based on 64 global model-based climate change simulations. On average, the results project small decreases in water levels over the 21st century (approximately 6 inches for Lakes Michigan and Huron and less for the other lakes). However, there is a wide range of uncertainty. 14
Prolonged periods of both high and low water levels in the future, like those observed over the past decade, should be anticipated.
For the latest information and data regarding lake levels, please consult the GLERL Great Lakes Water Level Dashboard
- Buttle, J., T. Muir, J. Frain, 2004: Economic Impacts of Climate Change on the Canadian Great Lakes HydroElectric Power Producers: A Supply Analysis, Canadian Water Resources Journal, 29:2, 89-110, DOI: 10.4296/cwrj089
- Millerd, F., 2005: The Economic Impact of Climate Change on Canadian Commercial Navigation on the Great Lake. Canadian Water Resources Journal. 30. 269-280. 10.4296/cwrj3004269.
- 3.P. L. Lawrence, J. Gordon Nelson, 1994: Flooding and erosion hazards on the ontario great lakes shoreline: a human ecological approach to planning and management, Journal of Environmental Planning and Management, 37:3, 289-303, DOI: 10.1080/09640569408711977
- U.S. Army Corp of Engineers. Monthly Mean Water Levels, https://www.lre.usace.army.mil/Portals/69/docs/GreatLakesInfo/docs/WaterLevels/LTA_GLWL-English_2019.pdf?ver=2020-02-04-152044-737
- NOAA. Record increase in Great Lakes water levels. https://www.regions.noaa.gov/great-lakes/index.php/highlights/record-breaking-increase-in-great-lakes-water-levels/
- Gronewold, A. D., R.B. Rood, 2019: Recent water level changes across Earth’s largest lake system and implications for future variability. Journal of Great Lakes Research, 45(1), 1-3
- Pendleton, E.A., E. R. Thieler, S. J. Williams, 2010: Importance of Coastal Change Variables in Determining Vulnerability to Sea- and Lake-Level Change. Journal of Coastal Research, 26, 1: 176 – 183
- Lofgren, B.M., F.H. Quinn, A.H. Clites, R.A. Assel, A.J. Eberhardt, 2000: Water Resources, in Sousounis, P.J., Bisanz, J.M. [Eds], Preparing for a changing climate– The potential consequences of climate variability and change, Great Lakes overview. USGCRP
- Hanrahan J.L., S.V. Kravtsov, P.J. Roebber, 2010: Connecting past and present climate variability to the water levels of Lakes Michigan and Huron. Geophysical Research Letters 37:L01701. DOI: 10.1029/2009gl041707.
- Croley T.E.I., 2003: Great Lakes Climate Change Hydrological Impact Assessment: IJC Lake Ontario—St. Lawrence River Regulation Study. Technical Memorandum. Water Resources Management Decision Support. NOAA Great Lakes Environmental Research Laboratory, Ann Arbor, MI 126:84
- IUGLS, 2009: Impacts on Upper Great Lakes Water Levels: St. Clair River. Final Report to the International Joint Commission.
- Gronewold, A.D., A. H. Clites, J. Bruxer, K. W. Kompoltowicz, J. P. Smith, T. S. Hunter, C Wong, 2015: Water Levels Surge on the Great Lakes, EOS. https://eos.org/science-updates/water-levels-surge-on-great-lakes
- Lofgren, B. M., T. S. Hunter, J. Wilbarger, 2011: Effects of using air temperature as a proxy for potential evapotranspiration in climate change scenarios of Great Lakes basin hydrology. J. Great Lakes Res., 37, doi: 10.1016/j.jglr.2011.09.006
- Lofgren, B. M., J. Rouhana, 2016: Physically plausible methods for projecting changes in Great Lakes water levels under climate change scenarios. Journal of Hydrometeorology, 17 (8), 2209–2223. doi:10.1175/jhm-d-15-0220.1.