Systemic Flood Risk Management Planning: A decision-support framework for large-scale flood risk management accounting for risk-distribution across flood-protected areas and deeply uncertain hydraulic interactions

Floods are natural phenomena which have potentially catastrophic effects on societies and their economies. Flood losses have been increasing in the last years and they are expected to increase further in the future due to climatic and socio-economic changes. It is therefore paramount to design measures and plan strategies (i.e. combination of measures) to limit flood losses. The current practice of designing flood risk management strategies adopts a risk-based approach, which recognizes that losses from floods cannot be reduced to zero but, at best, to a tolerable level against acceptable costs. Typically, a risk-based approach to flood risk management allows choosing measures by comparing them based on investment costs and effectiveness in reducing flood risk. A measure can e.g. be evaluated based on total societal costs, i.e. the sum of investment costs and the residual flood risk, with the most desirable measure being the one which minimizes total costs. In addition to minimizing total costs, objectives related to reducing individual risk or societal risk might also be applied. Although the risk-based approach aims at wisely allocating economic resources while, at times, also guaranteeing basic individual safety as well as avoiding large societal flood losses, it often neglects that measures implemented at one location may affect flood risk elsewhere. Acknowledging this was a reason for scientists and policy makers to advocate a move towards a comprehensive system approach. Such approach supports system-wide flood risk management planning and fully accounts for hydraulic interactions, i.e. the effects on hydraulic loading at one area due to events, e.g. response of the embankment to hydraulic loading or implementation of measures, occurring elsewhere. Two challenges are identified as crucial in adopting such a comprehensive system approach while accounting for hydraulic interactions.