Geographic inequalities in water distribution can lead to relatively small regions driving or buffering changes in water availability in major watersheds. This research provides a baseline quantification of water distribution in Alberta, Canada, and evaluates changes in water yield, streamflow timing, and climate from 1976 to 2015. Annual water yields for 77 contributing watershed areas were calculated and assessed for trends, and 45 unregulated watersheds were evaluated for changes in key streamflow timing metrics. Mountain headwaters supply 22–38% of annual flow of major rivers, while plains watersheds provide relatively low annual yield. Annual yield and precipitation decreases dominated northern watersheds, with increases in southern watersheds, and mixed trends in central watersheds. Later spring freshet timing and earlier onset of the low flow season were detected for most watersheds, leading to more water over a shorter duration when paired with increasing yield, and water losses in late summer-autumn when paired with decreasing yield. Yield and flow timing metrics are strongly related to precipitation with temperature as a secondary driver, except freshet timing, which is driven by spring temperature. This study provides comprehensive information about geographic drivers of changing water distribution and quantifies the disparity between regions of water surplus and deficit.