This paper assesses the effect of climate change on water availability for consumptive use for a river basin taking into account the regulation capacity of its water supply systems and a set of management standards (restrictions, demands, reliability). A specific sensitivity index to climate change defined by the relation between the unitary variation of water availability and the unitary variation of the average annual inflow is studied. The analysis is conducted by constructing climate projections taking into consideration changes only in mean annual streamflow and changes in both the mean and the coefficient of variation of the annual streamflow. The study area includes 567 basins which cover practically the entire territory of continental Spain. The results show a significant sensitivity to changes in the coefficient of variation for regulated systems.