Groundwater Availability

Water Availability

  • 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. 
Projected change in the number of consecutive dry days per year by mid-century assuming continued increases in greenhouse gas emissions. Data from the Third National Climate Assessment, modified.

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

Surface Runoff

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.

Seasonal Distribution

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

Land use affects the long-term water budget of the region as well as the response of runoff to individual precipitation events. Natural landscapes more effectively buffer moisture, making it available to plants for longer and delaying the eventual runoff of water that does not undergo evapotranspiration. Grassland experiences less evapotranspiration than other land cover types, while forests allow the greatest amount of water to percolate into the surface soil. Especially in southern sections of the Great Lakes region, land cover has evolved from natural forests and grasslands to agricultural, suburban, and urban development. Impervious surfaces, such as asphault and concrete, inhibit water percolation through the surface and direct precipitation into localized, high-volume flows. Cultivated agricultural land has high evapotranspiration, but also high surface runoff. So, aside from the possibility of precipitation falling in more intense events, agricultural and built environments will amplify extreme streamflows during intense precipitation events.15