This document discusses approaches for designing critical infrastructure systems under uncertainty from socioeconomic and climate change. It suggests applying safety factors or designing flexible systems to deal with an uncertain future. Quantitative decision models were used to determine the optimal safety factor and measure the value of flexibility. The models showed the safety factor should be higher for inflexible systems and lower for flexible ones. Flexibility is more valuable when there is potential for significant learning and changes over the system's lifetime. The regulatory framework, such as requiring a risk-based versus rule-based approach, also influences design choices. The document concludes with design recommendations based on optimizing safety factors and valuing flexibility under different types and degrees of uncertainty.