Warming temperatures, changes in rainfall and runoff, and sea level rise have affected and will likely continue to affect water resources directly and indirectly. Global air temperature increases are coupled with important changes in components of the hydrologic cycle such as changes in evapotranspiration, changes in atmospheric water vapor, and changes in rainfall patterns. Critical changes will seriously affect water resource availability, influence groundwater recharge and storage, and cause changes in surface water and ground water quality. Understanding these changes is essential for identifying ways to adapt to degradation of water resources. Therefore, in this chapter we will focus on how climate change may affect surface and groundwater systems.