Investigations of the impact of climate change on water resources systems usually involve detailed monthly hydrological, climatological, and reservoir systems models for a particular system. The conclusions derived from such studies only apply to the particular system under investigation. This study explores the potential for developing a regional hydroclimatological assessment model useful for determining the impact of changes in climate on the behavior of water supply systems over a broad geographic region. Computer experiments performed across the United States reveal that an annual streamflow model is adequate for regional assessments which seek to approximate the behavior of water supply systems. Using those results, a general methodology is introduced for evaluating the sensitivity of water supply systems to climate change in the northeastern United States. The methodology involves the development of a regional hydroclimatological model of annual streamflow which relates the first two moments of average annual streamflow to climate and drainage area at 166 gaging stations in the northeastern United States. The regional hydroclimatological streamflow model is then combined with analytic relationships among water supply system storage, reliability, resilience, and yield. The sensitivity of various water supply system performance indices such as yield, reliability, and resilience are derived as a function of climatical, hydrological, and storage conditions. These results allow us to approximate, in general, the sensitivity of water supply system behavior to changes in the climatological regime as well as to changes in the operation of water supply systems.