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Hydrologic scientists and water resource managers often focus on different facets of flow regimes in changing climates. The objective of this work is to examine potential hydrological changes in the Upper Boise River Basin, Idaho, USA in the context of biophysical variables and their impacts a key variable governing administration of water resources in the region in an integrated way. This snowmelt-dominated, mountainous watershed supplies water to a semi-arid, agriculturally intensive, but rapidly urbanizing, region. Using the Envision integrated modeling framework, we created a hydrological model to simulate hydrological response to the year 2100 using six alternative future climate trajectories. Annual discharge increased from historical values by 6-24% across all simulations (with an average 13% increase), reflecting an increase in precipitation in the climate projections. Discharge peaked 4-33 days earlier and streamflow center of timing occurred 4-17 days earlier by midcentury. Examining changes in the date junior water rights holders begin to be curtailed regionally (the Day of Allocation), we found that the it occurs at least 14 days earlier by 2100 across all simulations, with one suggesting it could occur over a month earlier. These results suggest that current methods and policies of water rights accounting and management may need to be revised moving into the future.