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Climate Change Impacts:
Water Supply and Pollution
Michigan depends heavily on groundwater, fresh water from Lake Michigan, Lake Huron and Lake Superior, and on rainfall for agriculture, drinking, and industrial uses. The state's current population of about 10 million has increased at faster than projected rates over the past decade, and continues to grow. As population increases, so will pressure to increase water extraction—an already difficult debate in the region.

As climate change takes effect, projected changes in rainfall, evaporation, and groundwater recharge rates will affect all freshwater users. Among the potential impacts of climate change with implications for Michigan's water supply and pollution levels are:

• A Reduction in Groundwater Recharge
  Reduced summer water levels are likely to diminish the recharge of groundwater, cause small streams to dry up, and reduce the area of wetlands, resulting in poorer water quality and less habitat for wildlife.
  
  
• A Decrease in Lake Levels
  Changes in the precipitation cycle and seasonal temperatures will affect lake levels. Overall, increasing temperatures will lead to a decline in ice cover and a greater rate of evaporation, causing lake levels to decline. As lake levels drop, costs to shipping on the Great Lakes are likely to increase, along with costs of dredging harbors and channels and of adjusting docks, water intake pipes, and other infrastructure.
  
  
• An Increase in Extraction Pressure
  With growing populations and projected drops in lake and ground water levels, climate change is expected to exacerbate an already contentious debate on water withdrawals from the Great Lakes. Conflicts may intensify as water shortages develop and pressure increases for more water for irrigation, drinking, and other human uses.
  
  
• A Degradation of Wetlands' Flood-Absorbing Capacity
  Development and climate change will degrade the natural flood-absorbing capacities of wetlands and floodplains. More run-off in winter and spring from rain-on-snow events and in summer from intense downpours, cause increased flooding and erosion. These events in turn could increase pollution in lakes, rivers, and streams from municipal and farm run-off, which often enters surface waters untreated. Periodic droughts also concentrate sulfates and acids, and, when flushed into lakes during intense rains, increase acid stress in aquatic systems.