Integrating intermittent photovoltaic (PV) power into dispatchable hydropower has become a promising way in the modern power systems. Despite being two primary energies, their planning and management often does not consider the effects of climate change. To determine the size of a PV plant appropriate for integration into a hydropower system, this study developed a climate–hydrology–operation framework to identify system resilience in a changing climate. This bottom-up framework comprises four modules: (1) a weather generation and hydrology simulation module; (2) a GCMs forecast information module; (3) a hydro/PV integrated operation optimization module; and (4) a resilience evaluation module. With a case study of the China's Longyangxia hybrid hydro/PV power system, our analysis revealed conclusions as follows. (1) This complementary propertity of precipitation and radiation in the study area provides a driving mechanism for complementary operation of the hybrid power system. (2) Precipitation and radiation are the factors dominating the variation of the system reliability and economy under climate change, respectively. (3) The optimal size of the PV plant is 600–800 MW, in this range, the hybrid power system exerts an excellent operational capacity adaptive to climate change, and it performs satisfactorily in terms of reliability and economy.