Abstract. This study investigated how reservoir performance varied across different hydrogeologic settings and under plausible future climate scenarios. The study was conducted in the Santiam River basin, OR, USA, comparing the North Santiam basin (NSB), with high permeability and extensive groundwater storage, and the South Santiam basin (SSB), with low permeability, little groundwater storage, and rapid runoff response. We applied projections of future temperature and precipitation from global climate models to a rainfall-runoff model, coupled with a formal Bayesian uncertainty analysis, to project future inflow hydrographs as inputs to a reservoir operations model. The performance of reservoir operations was evaluated as the reliability in meeting flood management, spring and summer environmental flows, and hydropower generation objectives. Despite projected increases in winter flows and decreases in summer flows, results suggested little evidence of a response in reservoir operation performance to a warming climate, with the exception of summer flow targets in the SSB. Independent of climate impacts, historical prioritization of reservoir operations appeared to impact reliability, suggesting areas where operation performance may be improved. Results also highlighted how hydrologic uncertainty is likely to complicate planning for climate change in basins with substantial groundwater interactions.