Climate change is taking special attention among the economic agents, especially due to the uncertainties and risks associated with it. In countries with a significant share of renewables in their energy matrix, this phenomenon implies on challenges for the energy planning in future scenarios. In this context, this study establishes a correlation between energy security and climate change by understanding the ability to generate hydroelectric power in large-scale hydroelectric (HEP) and small hydroelectric plants (SHP), in the Alto Paranapanema Basin (São Paulo, Brazil), a region with rainfall anomalies and water flow changes due to climate change. This region was chosen based on its future scenarios on climate change, especially those of rainfall anomalies and change in water flow, using the Soil Moisture Accounting Procedure (SMAP) mathematical model. The water flow was simulated in the HidroLab model, resulting in the generation of hydroelectric power. The results indicated a loss of generation capacity, that can be attributed to negative anomalies of rainfall and its direct influence on river flow, which is a fundamental factor in hydropower generation. Thus, this study draws attention to the importance of considering climate vulnerability in energy planning now and in the future.