Un diagramme d'influence pour l'évaluation des risques d'inondations urbaines au travers des dangers de rejet pluvial dans des conditions non-stationaires

Urban flooding introduces significant risk to society. Decision-makers need to agree on how to adapt urban areas to flooding. Non-stationarity leads to increased uncertainty and this is shown to be difficult to include into actual decision-making. Transparent methods are needed to facilitate the decision-making process. The primary objective of this study was to develop a risk assessment and decision support framework for pluvial urban flood risk under non-stationary conditions using an Influence diagram (ID) which is a Bayesian network (BN) extended with decision and utility nodes. Non-stationarity is considered to be the influence of climate change where extreme precipitation patterns change over time. The overall risk is quantified in monetary terms expressed as expected annual damage (EAD). The network is dynamic inasmuch as it assesses risk at different points in time to evaluate the non-stationarity in the urban system. The framework provides means for decision-makers to assess how different decisions on flood adaptation affect the risk now and in the future. For the development of the BN we used the HUGIN software. The result from the ID was extended with a cost-benefit analysis defining the net benefits for the investment plans. We tested our framework in a case study where the risk for flooding was assessed on a railway track in Risskov (Aarhus). Drainage system improvements are planned for the area and our case study presents how the developed ID illustrates the increase in risk over time and the decrease in risk due to the planned improvement.