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Climate Change Impacts:
Water Supply and Pollution
Pennsylvania depends heavily on groundwater, fresh water from Lake Erie, and rainfall for agriculture, drinking, mining, and industrial uses. As the state's population of over 12 million continues to grow, pressure upon water resources will increase.

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

• 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.
  
  
• A Reduction in Groundwater Recharge
  Reduced summer water levels are likely to diminsh the recharge of groundwater, which will cause small streams to dry up. This, in turn, will reduce the area of wetlands and result in poorer water quality and less habitat for wildlife.
  
  
• 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.