The role of extremity of summer floods for the annual statistic

Abstract

<p>Within the annual maximum series (AMS), which is the basis for assessing most of the flood protection measurements, summer as well as winter flood events are included. However, these do not only differ in their flood generation but also in their statistical distribution. While the distribution of winter floods is mostly light-tailed, summer floods often show a heavy-tailed behaviour. A light-tailed behaviour leads to a bounded distribution, which means that winter floods cannot exceed a certain magnitude. Heavy-tailed distributions are unbounded and extrapolation to annualities of several hundred years can lead to infinitely large design floods.  A combination of these different tail behaviours in the AMS often leads to heavy-tail behaviour for the annual series. In a study of the large river basins of Rhine, Danube and Elbe we investigate the impact of summer floods on the AMS. Spatial patterns become visible that can be linked to weather patterns like Vb. Moreover, an impact of the catchment size can be seen, where larger catchments tend to have lighter tailed distributions and a smaller impact of summer floods.  The results are then compared concerning their causality using deterministic models that include dam failure and inundation and the role of tributaries is shown.</p>