Risk and urban disasters are complex phenomena. This complexity results from the notion of disaster as a vulnerability-hazard product, and the “domino effects” it generates. A disaster cannot only be limited to one or the other of its components, in so doing the system would be studied neither as a whole nor in its complexity. Whether they are of natural, technological, economical, or sanitary origin, hazard is mainly what is studied. On the other hand, studies relating to the vulnerability are more recent and exceptional ; research combining hazard and vulnerability is even more so. This article first proposes to introduce some steps that could be used by geographers in order to study the vulnerability and its critical stages. Then, in using a modelling and simulation method, called the “dynamic system”, it proposes an urban disaster model in relation to Mediterranean flooding. This model associates the various components of the disaster, namely, the hazard, the vulnerability and the “domino effects”. It is also enriched by a module of urban circulation. In this article, only the modules of vulnerability and vehicles flows will be subject of a detailed study. Lastly, in a third part, we present different graphic models representing the system of vulnerability as well as the advantages and drawbacks of various systemic approaches.