Advanced reactor concepts are proposed as a pathway to improve the economics of nuclear energy by modularizing, factory-fabricating, and standardizing designs, while enhancing safety through simplified systems and reliance on passive safety features. In this study, we focus on passive safety systems that perform critical safety functions, with particular emphasis on decay heat removal following reactor shutdown. Passive systems primarily rely on natural driving forces such as gravity, density and pressure differences, and natural convection. By reducing reliance on active safety systems and their supporting infrastructure, passive designs are expected to enhance overall safety. Nevertheless, these systems can still experience safety-relevant failures that must be investigated. For example, because their performance relies on relatively weak natural driving forces (such as gravity and natural circulation), passive systems can be more sensitive to degraded boundary conditions and external hazards that reduce heat-removal capability. Studies indicate that external natural hazards are expected to evolve due to non-stationary environmental conditions, potentially increasing the frequency and intensity of weather- and water-related hazards in certain regions. This study first evaluates the safety issues associated with passive safety systems used across advanced reactor technologies. Then it investigates how evolving external hazards can amplify these challenges and affect overall system performance.