Assessing the maximization potential for historical floods by spatio-temporal simulation of precipitation

The objective of this study is to investigate how large historical floods could become under “optimal” rainfall conditions, and which are the main factors that drive flood maximisation. Observed storms are stochastically modified to create an ensemble that enables sampling flood extremes. This stochastic modification entails first the amplification of the intensities, followed by modification of the spatial patterns of precipitation. The rainfall intensities are modified using moisture maximisation; the spatial patterns are changed by conditional rainfall simulation. The simulated precipitation is then used as input for a rainfall-runoff model to simulate corresponding floods. The methods are illustrated using flood event data from the Mulde river catchment in Germany. The results show that reasonable modifications on observed storms may lead to very extreme flood events. Additionally, the largest simulated precipitation events and floods can also be considered as plausible estimates of probable maximum precipitation and probable maximum flood, respectively.