Global climate change will likely alter the hydrologic cycle in ways that may cause substantial impacts on water resource availability and changes in water quality. For example, the amount, intensity, and temporal distribution of precipitation are likely to change. Warmer temperatures will affect the proportion of winter precipitation falling as rain or snow, how much is stored as snow and ice, and when it melts. Long-term climatic trends could trigger vegetation changes that would alter a region’s water balance. In forested areas, the combination of warmer temperatures and drying soils caused by earlier snowmelt or longer drought periods could cause wildfires to become more frequent and extensive. Where that occurs, land cover and watershed runoff characteristics may change quickly and dramatically as wildfires reduce forest cover, thereby altering the runoff response. Less dramatic but equally important changes in runoff could arise from the fact that the amount of water transpired by plants will change with changes in soil moisture availability, and plant responses to elevated CO2 concentrations. In addition, changes in the quantity of water percolating to groundwater storage will result in changes in aquifer levels, in base flows entering surface streams, and in seepage losses from surface water bodies to the groundwater system. There is a rich scientific literature describing the potential influence of climate change on both individual water cycle components and the overall hydrologic cycle.