Flood disaster theory is required to enable deeper understanding for the design of disaster risk reduction policies, generalisations to places where there are few or no studies, and as a contribution to the developing fields of socio-hydrology and coupled social-ecological systems. While there are several existing candidate conceptual frameworks and putative theories for parts of the complex system that is a disaster there is nothing approaching what might be called a master theory. It is most likely that a master theory can be constructed from the emergent properties of flood disasters. Flood peak discharges, flood sediments, and flood damage and deaths are emergent properties and are fractal. The working hypothesis is that the fractal properties of flood peaks, damage and deaths are a result of the fractal nature of the drainage network that produces floods and the fractal nature of the precipitation that falls on the drainage networks. If this hypothesis is found to be sound then human vulnerability is not just a function of human decisions and actions. Vulnerability and hazard are therefore not independent; throwing into disarray the basis of much flood disaster analysis policy. Empirical data from Thailand, India and northern Australia will be used for illustration.