Urban areas are becoming increasingly subject to and vulnerable to water-related natural disasters. Urban areas are a kind of socio-ecological system wherein the human development dynamics co-evolve with the natural dynamics. Most of the literature is focused on the impact of natural disasters on human development; we evaluate the impacts of human development on natural disasters and present an analysis of this phenomenon in the context of megacities. The approach is exploratory and begins with the construction of a database on the 595 existing megacities in the world. Multifactor analysis is then used to determine the main characteristics of these megacities. Finally, three structural components (maturity, anthropization and centrality) are identified and then correlated with data on water-related hazards, distinguishing groups of cities according to their structure and factors of vulnerability to water-related risks.