AbstractInterdependent infrastructure systems consist of several sectors, including gas, power, transportation, and health systems, and are important in modern societies because they provide essential services for the continuous functioning of communities and society. This study presents a framework for conducting vulnerability analyses and key sector identification in interdependent infrastructure systems during and after the occurrence of an external perturbation. To analyze the correlation of sectors and identify the key sectors at different stages of a hazard, this study introduces input-output models, demand-driven inoperability input-output models (IIMs), and supply-driven IIMs. Moreover, an interdependency matrix is used to construct the network in an interdependent infrastructure system, and new indicators of importance and vulnerability indexes are defined to analyze changes in key sectors in different periods of an external hazard. The proposed model is illustrated through a hypothetical four-sector interdependent infrastructure system based on a flash flood event. However, the model is applicable to any physically interdependent system, such as a transportation system, power supply system, and so on. The importance and vulnerability attributes of interdependent infrastructure systems at different stages of the risk management process also provide guidance for decision makers involved in dealing with natural hazards such as flash flood events.