- Despite increasing precipitation, land surfaces in the Great Lakes region are expected to become drier overall due to increasing temperatures and evaporation rates.
- More frequent droughts could affect soil moisture, surface waters, and groundwater supply.
- The seasonal distribution of water availability will likely change. Warmer temperatures may lead to more winter rain and earlier peak streamflows.
Groundwater is a critical source of water in the Great Lakes region, with as much groundwater as there is water in Lake Michigan.1 Though counterintuitive, some areas may experience reduced water supplies during summer months even as annual total precipitation is expected to increase throughout the region. As temperatures rise, increasing evaporation may outpace increases in precipitation and elevate drought risk, particularly in areas that are already susceptible.2 While decreases in summer groundwater supply are predicted overall, model projections of water availability and ground water recharge vary widely on the timing, magnitude, and location of such changes.3 4
Groundwater Supply and Soil Moisture
Higher temperatures and evaporation rates decrease soil moisture and groundwater supply.5 6 7 8 3 Parts of the region could see as much as a 30-percent decrease in soil moisture that would be felt most strongly in summer, when groundwater recharge could be decreased most severely, and more low-flow periods and droughts become more likely.3 7 8
Water Usage Conflicts
Reduced water availability could create greater conflict over limited water resources, as has happened in other parts of the United States, and responding to changes in water supply and demand distribution would be costly.9 For example, some projections suggest Minnesota could suffer a loss of wetlands from increased evapotranspiration. In that case, diminished water supplies would have to be shared more heavily between human use and wetland protection.5
Runoff may become flashier and more sporadic, decreasing at times due to less soil moisture and groundwater, but increasing at other times due to more intense precipitation. 4 This carries significant implications for public health, water quality, and marine wildlife.
The seasonal distribution of water availability will also most likely change. Between 1920 and 1995, input into Lake Michigan and Huron has shifted to autumn and winter, resulting in less runoff and lake-level rise in the spring.10 In Lake Superior, however, decreased runoff has been observed during the autumn and summer, and no change in runoff has been seen in winter and spring, suggesting seasonality in Lake Superior lake levels has decreased. 11 Warmer temperatures are expected to affect winter precipitation in the future. More winter rain would mean earlier peak flows, more runoff in autumn and winter, and less runoff in the spring.10 12 13 4 14 Stream flow could be highly variable in the early- and mid-century (2010-2069) but increase by late-century (2070-2099). This would include an increase in winter and spring flows, and more variability and flashiness in summer flows, reflecting more extreme precipitation events.12
Land Use and Water Supply
- 1. IJC. (2010) Groundwater in the Great Lakes Basin. International Joint Commission, Washington, DC, Ottawa, ON, and Windsor, ON.
- 2. Pan, Z., and S. C. Pryor, 2009. Overview: Hydrologic regimes. In Understanding Climate Change: Regional Climate Variability, Predictability, and Change in Midwestern USA, S. Pryor, ed., Indiana University Press, 88-99.
- 3. a. b. c. Wuebbles D.J. (2006) Executive Summary Updated 2005: Confronting Climate Change in the Great Lakes Region. Union of Concerned Scientists.
- 4. a. b. c. 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.
- 5. a. b. Frelich L., Phillips-Mao L., Galatowitsch S. (2009) Regional climate change adaptation strategies for biodiversity conservation in a midcontinental region of North America. BIOLOGICAL CONSERVATION 142:2012.
- 6. Hayhoe K., Weubbles D.J. (2008) Climate Change and Chicago: Projections and Potential Impacts. Report for the City of Chicago.
- 7. a. b. Hayhoe K. (2007) Past and future changes in climate and hydrological indicators in the U.S. Northeast. Climate Dynamics 28:381–407.
- 8. a. b. Karl T.R., Melilo J.M., Peterson T.C. (2009) Global Climate Change Impacts in the United States. USGCRP.
- 9. Frederick K., Schwarz G. (2000) Socioeconomic Impacts of Climate Variability and Change on US Water Resources. USGCRP Discussion Paper 00-21:87.
- 10. a. b. Argyilan E., Forman S.L. (2003) Lake level response to seasonal climatic variability in the Lake Michigan–Huron system from 1920 to 1995. Journal of Great Lakes Research 29:488–500.
- 11. Lenters J.D. (2004) Trends in the Lake Superior Water Budget Since 1948: A Weakening Seasonal Cycle. Journal of Great Lakes Research 30:20.
- 12. a. b. Cherkauer K.A., Sinha T. (2010) Hydrologic impacts of projected future climate change in the Lake Michigan region. Journal of Great Lakes Research 36:33-50. DOI: 10.1016/j.jglr.2009.11.012.
- 13. Mortsch L.D. (2000) Climate Change Impacts on the Hydrology of the Great Lakes -St. Lawrence System Canadian Water Resources Journal 25:121-179. DOI: 10.4296/cwrj2502153.
Shmagin and Johnston, 2008
- 14. Allen, J.D., Hung, V. (2000). Water Ecology FOCUS: Climate Change and River Flows, 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, pp. 51-54.
- 15. Lofgren, B. and A. Gronewold, 2012: Water Resources. In: U.S. National Climate Assessment Midwest Technical Input Report. J. Winkler, J. Andresen, J. Hatfield, D. Bidwell, and D. Brown, coordinators. Available from the Great Lakes Integrated Sciences and Assessments (GLISA) Center.