Compound Flood Events: Analysing the joint occurrence of extreme river discharge events and storm surges in Northern and Central Europe

Abstract. The simultaneous occurrence of extreme events gained more and more attention from scientific research in the last couple of years. These compound extreme events have an increased damage potential, compared to the separate occurrence of extreme events, and became a core topic in risk assessment. It is important to improve our understanding of the underlying mechanisms that can cause compound flood events. Our study focuses on the analysis of potential compound flood events with the following contributions. First, we introduce a Monte–Carlo approach to analyse flood event probabilities in northern and central Europe without the use of copulas or ensembles. Second, we investigate if the number of observed compound extreme events is within the expected range of two standard deviations of randomly occurring compound events. This includes variations of several parameters to test the stability of the identified patterns. Finally, we analyse if the observed compound extreme events had a common driver. The results of our investigation show that rivers along the western facing coasts of Europe experienced a higher amount of compound flood events than expected. In these regions, the vast majority of the observed potential compound flood events seem to be related to the Großwetterlage Cyclonic Westerly.