ABSTRACT
Over the past 50 years, the world has faced dramatic growth of its urban population. The percentage of urban inhabitants exceeded the rural population for the first time in 2007. Furthermore, the trends imply that almost all the expected world population growth until 2030 will be absorbed by urban areas (United Nations, 2003). From 1975 up to the present, the number of so-called megacities increased from 4 to 22, mostly in less developed regions (Münchner Rück, 2005). In general, the term “megacity” describes the world’s largest agglomerations. Quantitatively, megacities are defined as megalopolises with more than 10 million inhabitants (United Nations, 2003; Mertins, 1992). Qualitatively, megacities are characterized by high and dense population concentration, and a high density of industries, and social, technical, and transportation infrastructure. They show extreme, uncontrolled urban sprawl, high traffic pressure, ecologic overload, concentration of assets
and power, high spatiotemporal dynamics, and the coexistence of socioeconomic disparities (Kötter, 2004; Kraas and Coy, 2003). In these megacities, in particular, the enormous dimension of quantitative growth, the high concentration of people, infrastructure, and economic power, but also the synchronism, complexity, and interaction of diverse urban processes, imply nonassessable risks. Thus, megacities can be both victims and producers of risks.
