Return period of extreme summer precipitation in the Meuse Basin

In July 2021 a cut-off low pressure system caused extreme daily precipitation sums, leading to high water levels in the Meuse River and floods in some of its tributaries. Probability estimates of such an extreme precipitation event have a high statistical uncertainty due to limited number of observations. The lack of knowledge on the atmospheric dynamics driving those extreme events, further increases the uncertainty on return period estimates. To reduce this uncertainty, we used the physics based synthetic database SEAS5, which largely increases the amount of data available. Using SEAS5, we successfully reduced statistical uncertainty and found that the most extreme summer precipitation events are driven by a different dynamical process than ‘general’ extremes. Consequently, the risk of an event such as 2021 can be underestimated when not considering the underlying atmospheric dynamics.