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Climate Change Impacts:
Water Supply and Pollution
A warming climate is projected to result in changes in rainfall patterns, evaporation rates, and groundwater recharge. These changes will affect residential, agricultural, and industrial users of fresh water. Demand for fresh water will rise as Illinois's population increases to an expected 13.5 million residents by 2025.

Competing demands on limited water resources due to growth alone will increase freshwater management challenges with or without climate change. Climate change could complicate this situation, since any shift in rainfall, evaporation, groundwater recharge rates, and runoff patterns would affect ecosystems and all users of fresh water. Among the potential impacts of climate change with implications for water supply and pollution levels in Illinois are:

• A Reduction in Groundwater Recharge
  Reduced summer water levels are likely to diminish the recharge of groundwater, cause small streams to dry up, as well as 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. Increasing temperatures will lead to a decline in ice cover and a greater rate of evaporation causing drops in lake levels in both Lake Michigan and inland lakes. 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.
  
  
• An Increase in Risk of Water-Borne Diseases
  Warmer water temperatures and increased run-off from extreme rainstorms will likely increase the risk of the spread of parasitic and pathogenic microorganisms by way of that local water supply, as well public beaches.