This study's objective is to assess the potential impact of climate change on an example under-design hydropower system in the Karkheh River basin, Iran. Based on three water resources performance criteria (reliability, resiliency, and vulnerability), a novel framework was proposed to interpret and cope with the uncertainties associated with such assessments. The results demonstrated the acceptable performance of the system in most months, while there were certain signs for rare low-inflows, and consequently low hydropower generated by the system, due to the climate change. It was found that in terms of these three criteria, the best performances in the climate-change condition occurred in May (80% reliability), December (45% resiliency), and April (19% vulnerability). Yet the worst performances occurred in September (2% reliability), July and August (0% resiliency), and in October (39% vulnerability). These results indicated that the reliability and resiliency of the system would be improved under the climate change condition, while due to the increase of low-inflow incidences, the vulnerability of the system would increase. This suggests that, although the system may not face frequent failures, severe blackouts may occur. With timely consideration of future climatic conditions and appropriate adaptive actions, including additional backup systems for reliable and safe electricity generation, future undesired conditions can be avoided in the basin.