Uncertainty and Disaster Risk Management: Modeling the Flash Flood Risk to Vienna and Its Subway System

This report describes an interdisciplinary approach to flood risk analysis and management that was developed by investigating flood risks in the city of Vienna, Austria. The purpose of the research was to analyze different policy paths (including both flood-prevention measures and risk-sharing financial provisions) in the presence of major uncertainties. A preliminary analysis resulted in the identification of two major methodological issues that needed to be resolved, namely: -- The concept of risk used in flood management varied subtly but significantly across the disciplines contributing to the assessment. -- Current assessment procedures did not give a full account of uncertainties and their different types. For those reasons an approach was developed that allows the analyst: (1) to integrate the different diciplinary concepts of risk within a single interdisciplinary analysis; and (2) to take into account uncertainties in a way that not only allows their many characteristics to be distinguished but is also consistent across the component disciplines. The focus of this report is the phenomenon of flash flooing of the Vienna River. Our analysis demonstrated that, in this case, the greatest damage from flash flooding was to be expected in the Vienna city subway system. The report thus describes a detailed assessment of the flood risk to the subway and of related management measures, on which research to date has been scarce. The results show that an approach based on catastrophe modeling and Monte Carlo simulation can not ony integrate the risk perspectives of the different technical disciplines contributing to this study but also provide a useful framework for comparing the characteristics of different mitigation strategies. The results of the simulations suggest alternatives for combining different mitigation measures to ensure complementarity among the characteristics of different components of an overall strategy, and thereby decrease total costs and reduce the likelihood and the uncertainties of catastrophic financial losses