For the Complete Methodology: Download Chapter
In studying where and how communities might be at risk for different climate futures for flooding, it is necessary to understand the unique dynamics of flooding in the Great Lakes and to develop methods to identify and map high risk areas or high energy waves. This chapter provides a brief explanation of Great Lakes dynamics and the potential impact of climate change on the Great Lakes region; this information is useful in informing potential flood projections. Additionally, this chapter includes by a detailed step-by-step guide that will enable each community to develop its own set of flood scenarios using publicly-available data.
Background and Considerations
Great Lakes Dynamics
The Great Lakes function differently than other inland water bodies and tidal oceans. Great Lakes water level changes result not from the moon’s gravitational pull, but from cyclical changes in rainfall, evaporation, and riverine and groundwater inflows.(1) These factors work together to raise and lower the water levels of the Great Lakes in small increments daily, seasonally, and over the course of years and decades. Long-term water levels fluctuate by multiple feet.
Since the early 2000s, the Great Lakes’ water levels have remained low, but historical patterns over the last century indicate higher water levels are sure to return.(2) Lake Michigan’s water level in October 1986 averaged 582 feet while in January 2013, the water level averaged 576 feet. However, since 2013, water levels have risen, averaging 580 feet as of June 2016.(3) The decadal and multi-decadal shifts in water levels are not solely responsible for the movement of the shoreline landward and lakeward over time. The velocity and height of waves, erosion of shorelines, and variability in the oscillation of water levels also contribute to coastal dynamics on the Great Lakes.
The Great Lakes are subject to high energy waves and wave setup along the coastline. High energy waves are strong in speed and intensity and are primarily created as fast winds move across the surface of the water for extended distances.(4) Wave setup is the height of the water as waves reach the shore. High wave setup results as regional storm patterns create high winds on the bounded water bodies of the Great Lakes. These powerful and tall waves are natural conditions that can increase the pace of erosion and damage structures on or near the shoreline.(5)
The shorelines of Lake Michigan are mostly made of gravel and sands that easily erode during times of high energy waves.(6) Coastal erosion can flood and damage infrastructure along bluffs and beaches and is a natural occurrence on the geologically young Great Lakes. Erosion is caused mainly by storms and winds, not necessarily by rising lake levels.(7)
The Great Lakes are contained in gradually shifting and tilting basins. This tilting results as the Earth slowly decompresses and rebounds from the immense weight of the glaciers that created the Great Lakes.(8) This attribute of the Great Lakes contributes to the difficulty of predicting the pace of shoreline movement. Therefore, it is safest to plan for great variability and rapid change in water levels.(9)
Powerful waves, erosion, and quickly changing shorelines are natural processes of the Great Lakes, each having implications for planning efforts along the coast. Climate change, however, augments these natural processes, and requires preemptive planning in coastal communities.
Climate and weather are directly related, but are not the same thing. Weather refers to the day-to-day conditions in a particular place, like sunny or rainy, hot or cold. Climate refers to the long-term patterns of weather over large areas. When scientists speak of global climate change, they are referring to changes in the generalized, regional patterns of weather over months, years and decades. Climate change is the ongoing change in a region’s general weather characteristics or averages. In the long term, a changing climate will have more substantial effects on the Great Lakes than individual weather events.
Evidence collected over the last 150 years shows a trend toward a higher global temperatures, higher sea levels, and less snow cover in the Northern Hemisphere. Scientists and ecologists from many fields have observed and documented significant changes in the Earth’s climate. Warming of the climate system is unequivocal and is now expressed in higher air and ocean temperatures, rising sea levels, and melting ice.(10)
The Great Lakes Integrated Sciences & Assessments Center (GLISA) is a consortium of scientists and educators from the University of Michigan and Michigan State University that provides climate models for the Great Lakes Region in support of community planning efforts. According to GLISA, the Great Lakes region experienced a 2.3 degree Fahrenheit increase in average air temperatures from 1900 to 2012.(11) An additional increase of 1.8 to 5.4 degrees Fahrenheit in average air temperatures is projected by 2050. Although these numbers appear relatively small, they are driving very dramatic changes in Michigan’s climate and greatly impact the Great Lakes.(12)
There is strong consensus among climate experts that storms, greater in number and intensity, will occur in the Great Lakes region.(13) This is already happening as “the amount of precipitation falling in the heaviest 1% of storms increased by 37% in the Midwest and 71% in the Northeast from 1958 to 2012.” (14) As storms drop more precipitation and generate stronger sustained winds, the Great Lakes will see stronger and higher waves.(15) In addition to direct damage caused by storms, sustained increases in the number of storms and their intensity can both directly and indirectly pollute waters by overloading sewage and stormwater capabilities.(16) Increases in the intensity of storms also quickens the pace of erosion on Great Lakes shorelines. In fact, the Federal Emergency Management Agency (FEMA) projects approximately 28% of structures within 500 feet of a Great Lakes shoreline are susceptible to erosion by 2060.(17)
The natural ups and downs in the water levels of Lake Michigan will continue regardless of the impacts of climate change.(18) However, climate change is likely to augment this natural process resulting in more variable water levels as warmer air temperatures result in fewer days of ice cover and faster evaporation.(19) In other words, lake levels could rise and fall faster and with even less predictability than in the past. Fortunately, much of Michigan’s coastal infrastructure was built in previous decades during times of high water levels.(20)
However, fast rising waters can erode shorelines, damage infrastructure, and cause extensive flooding in inland rivers.(21) When lake levels fall, access to infrastructure like docks may be restricted and navigation hazards in shallow waters are exposed. Low lake levels pose a threat to coastal vegetation and can reduce the pumping efficiency of drinking water intake pipes.(22) Additional ramifications of changing lake levels include a drop in water supply, restricted fish habitats, more invasive species, faster erosion, and an overall decline in beach health.(23) Climate change is likely to augment the natural highs and lows of lake levels, causing more variability and a faster rate of change, making each of these potential ramifications both more likely and less predictable.
(1) Norton, Richard K. , Meadows, Lorelle A. and Meadows, Guy A.(2011) ‘Drawing Lines in Law Books and on Sandy Beaches: Marking Ordinary High Water on Michigan’s Great Lakes Shorelines under the Public Trust Doctrine’, Coastal Management, 39: 2, 133-157, First published on: 19 February 2011 (iFirst)
(2) Meadows, Guy A., and Meadows, Lorelle A., Wood, W.L., Hubertz, J.M., Perlin, M. “The Relationship between Great Lakes Water Levels, Wave Energies, and Shoreline Damage.” Bulletin of the American Meteorological Society Series 78: 4. (1997): 675-683. Print.
(4) National Oceanic and Atmospheric Administration. “Coastal Currents.” Ocean Service Education. NOAA, 25 March 2008. Web. Accessed July 2015.
(5) Norton, Richard K. , Meadows, Lorelle A. and Meadows, Guy A.(2011) ‘Drawing Lines in Law Books and on Sandy Beaches: Marking Ordinary High Water on Michigan’s Great Lakes Shorelines under the Public Trust Doctrine’, Coastal Management, 39: 2, 133-157, First published on: 19 February 2011 (iFirst)
(7) Meadows, Guy A., and Meadows, Lorelle A., Wood, W.L., Hubertz, J.M., Perlin, M. “The Relationship between Great Lakes Water Levels, Wave Energies, and Shoreline Damage.” Bulletin of the American Meteorological Society Series 78: 4. (1997): 675-683. Print.
(8) Dorr, J. A., and D. F. Eschman. 1970. Geology of the Great Lakes. Ann Arbor: University of Michigan Press.
Wilcox, D.A, Thompson, T.A., Booth, R.K., and Nicholas, J.R., 2007, Lake-level variability and water availability in the Great Lakes: U.S. Geological Survey Circular 1311, 25 p
(10) Intergovernmental Panel on Climate Change. (2007). Observed changes in climate and their effects. Web. Accessed July 2015.
(11) Great Lakes Integrated Sciences and Assessments (2015). Temperature. Web. Accessed July 2015.
(13) U.S. Global Change Research Program. Global Climate Change in the United States, 2009. Cambridge University Press, Cambridge.
(14) Mackey, S. D., 2012: Great Lakes Nearshore and Coastal Systems. In: U.S. National Climate Assessment Midwest Technical Input Report. J. Winkler, J. Andresen, J. Hatfield, D. Bidwell, and D. Brown, coordinators.
(15) Great Lakes Integrated Sciences and Assessments. Climate Change in the Great Lakes Region. GLISA, 2014. Web. Accessed July 2015.
(16) Cruce, T., & Yurkovich, E. (2011). Adapting to climate change: A planning guide for state coastal managers–a Great Lakes supplement. Silver Spring, MD: NOAA Office of Ocean and Coastal Resource Management.
(17) The Heinz Center. (2000). Evaluation of Erosion Hazards. Web. Accessed July 2015.
(18) Dinse, Keely. Preparing for Extremes: The Dynamic Great Lakes. Michigan Sea Grant. Web. Accessed July 2015.
(19) Cruce, T., & Yurkovich, E. (2011). Adapting to climate change: A planning guide for state coastal managers–a Great Lakes supplement. Silver Spring, MD: NOAA Office of Ocean and Coastal Resource Management.
(20) Dinse, Keely. Preparing for Extremes: The Dynamic Great Lakes. Michigan Sea Grant. Web. Accessed July 2015.
(23) Cruce, T., & Yurkovich, E. (2011). Adapting to climate change: A planning guide for state coastal managers–a Great Lakes supplement. Silver Spring, MD: NOAA Office of Ocean and Coastal Resource Management.
Dinse, Keely. Preparing for Extremes: The Dynamic Great Lakes. Michigan Sea Grant. Web. Accessed July 2015.