Development of a Catastrophe Model for Managing the Risks of Urban Flash Flooding in Vienna

This report provides a case study examining flood risks in the city of Vienna. The purpose is to illustrate an interdisciplinary approach to flood risk analysis, combining hydrological flood risk assessment and simulation modeling with the finances of flood risk management. Three scenarios were preliminarily identified for analysis: catastrophic flooding on a major European river (the Danube) that flows through Vienna; storm flooding due to failure of storm drainage systems; and flash flooding of a small tributary (the Vienna River) that flows into the Danube. Our initial efforts revealed that the Vienna River flash flooding scenario was a credible, significant, and tractable problem for analysis. The wealth of data available also made this scenario a useful test case for developing and illustrating interdisciplinary work, which is a significant aspect of the project activity. The focus of this report is, therefore, on the flash-flooding scenario. This report does not include discussion of the other scenarios, as they were not completed in an interdisciplinary fashion either because of lack of adequate data and models for all aspects of an interdisciplinary study, or because there were judged to be non-credible and therefore of limited use as an illustrative example. In the course of developing an interdisciplinary approach to examining catastrophic flood risks, we found that the concept of risk used in flood management varied subtly but significantly between the disciplines contributing to the study. An important result of this study is the integration of these different disciplinary concepts of risk within a single interdisciplinary analysis. A fuller accounting for uncertainty in a way that is consistent between the component disciplines, and the appropriate distinction between various different types of uncertainty, form a second major aspect of the study. Our primary finding is that an approach that integrates perspectives on risk characteristic of the different technical disciplines contributing to this study is feasible and that it provides a useful framework for comparing the characteristics of different mitigation strategies. The results of simulations suggest alternatives for combining different mitigation measures such that the characteristics of different components of an overall strategy complement each other to lower total costs and to reduce both the likelihood and the uncertainties of catastrophic financial losses.