Handling uncertain events that could happen anytime and anywhere and dealing with many complex systems interconnected physically and socially makes Disaster Management (DM) a multidisciplinary endeavor and a very difficult domain to model. In this paper we present a development and validation of a Disaster Management Metamodel (DMM), a language that we develop specific for describing DM domain. The metamodel, a precise definition of the constructs and rules needed for creating the semantic models of DM domain consists of four views based on four DM phases including Mitigation, Preparedness, Response and Recovery-phase classes of concept. A Model Importance Factor (MIF) criterion is used to identify 10 existing disaster management models to evaluate the expressiveness and the completeness of DMM. The paper presents the synthesis process and the resulting metamodel, as a foundational component to create a Disaster Management Decision Support System (DMDSS) to unify, facilitate and expedite access to DM expertise.