Recent changes in global climate, and especially changes in precipitation patterns, may negatively impact on siltation of Andean storage reservoirs, thereby putting at risk the provision of resources to the local population. The extent to which this may happen is poorly understood. We therefore studied the catchment of the Cañete River in the western Peruvian Coastal Range as it plays an important role in the socioeconomic development of the region. It houses the 220 MW El Platanal hydroelectric plant and the Capillucas reservoir that provide the surrounding areas with water and energy. We used a hydrological model (HEC-HMS) coupled with a sediment transport model (HEC-RAS) to simulate future changes in river discharge and sediment load. This information was then used to calculate the siltation of the Capillucas storage reservoir. Ten scenarios were developed, a combination of two different precipitation patterns and five different precipitation rates. The precipitation patterns differed in the distribution of the precipitation change during the rainfall season, and the precipitation rates differed in the extent of change in precipitation amounts. The average sediment load of the Cañete River was estimated at 981 kTon/yr upstream of the Capillucas reservoir and showed that the calculated life span of the Capillucas reservoir is about 17 years. The most pessimistic scenario suggested a reduction in the life span of the reservoir to 7 years and the most optimistic scenario to 31 years. Even under the most optimistic scenario, the life span of the reservoir is shorter than its officially expected functionality of 50 years. As such, our results demonstrated the vulnerability of Andean hydroelectric reservoirs against future climate change.