A consistent set of trans-basin floods in Germany between 1952–2002

Abstract

Abstract. Floods that affect many sites simultaneously can pose great challenges in the co-ordination of flood disaster management actions, as well as for the insurance and reinsurance industry, since this type of flooding leads to an accumulation of losses and the risk assessment needs to be extended to a concept representing the spatial risk of flooding. The assessment of the accumulated risk, especially over large domains, requires an analysis of the spatial and temporal coherence of flooding. For Germany the extent of spatial dependence of flooding is largely unknown and no systematic analysis has been performed so far. In this paper, we present a methodology that is capable of capturing the simultaneous occurrence of flooding using multiple series of mean daily discharge. For the first time we present a complete and consistent set of trans-basin floods in Germany for the period between 1952 and 2002. Each flood is characterised by a specific value for the timing, the location and the magnitude of discharges within the entire river network. We propose a measure for quantifying the overall event severity considering both the heterogeneous spatial extent as well as the locally varying magnitudes of a trans-basin flood. In total, we identify 80 trans-basin floods in the entire time period. The set is dominated by events that were recorded in the hydrological winter (64%); 36% occurred during the summer months. 32 events affected more than one third of the entire river network. These most severe events are predominantly winter events. Dividing the study period into two sub-periods, we find an increase in the percentage of winter events from 58% in the first to 70.5% in the second sub-period. Accordingly, we find a significant increase in the number of extreme trans-basin floods in the second subperiod. A natural extension of this study is the quantification of the spatial and temporal dependencies in a multivariateCorrespondence to: S. Uhlemann (uhlemann@gfz-potsdam.de) framework. This framework needs to be supported by a flood typology based on the analysis of the physical processes relevant in the genesis of trans-basin floods.

Data expansion: the potential of grey literature for understanding floods

“…5, where magnitude is expressed as the exceedance of a certain return period at a certain number of stations (using the 162 gauges of Uhlemann et al, 2010). If return periods were encountered that equalled or exceeded the 50-yr flood, almost certainly at least one report was produced and made accessible, and at a level of the 20-yr flood the publication of a report is very likely.…”

“…Also (personal) experience reports or narratives are not included. As most river basins in Germany have significant upstream reaches in other countries it is useful to evaluate search hits also from Austria (Danube), Switzerland (Rhine) and the Czech Republic (Elbe) and to a very limited degree from Poland (Odra) (none of the top 40 floods in the trans-basin flood event set exhibited major flooding at the Odra; compare to Uhlemann et al, 2010). If no additional information on source, pathways, receptors and/or consequences in Germany is obtained from these documents, they are not included in the results list.…”

“…Transbasin summer floods are characterized by high local magnitude, often with record-breaking rainfall intensities, flashflood characteristics in headwater catchments and high damages including fatalities. Uhlemann et al (2010) provide an index of severity that allows comparing events according to their spatial extent and their patterns of magnitude. Using this index, Fig.…”

“…Therefore, instead of aiming to conduct a complete search for flood-relevant publications we rather aim for consistency in the search approach. The task at hand for this study is phrased as follows: Identify all studies that contain information on the sources, pathways, receptors and/or consequences (SPRC) for any of the top 40 flood events contained in the set of trans-basin floods (Uhlemann et al, 2010) and concerning the territory of Germany. This task at hand and the expectation of consistency thus impose several logical constraints to the choice of search terms, the search strategy and the formulation of the inclusion criteria.…”

“…Trans-basin floods are extreme events occurring on a regional scale and across catchment boundaries. We aim at creating an openly accessible database of the metadata of publications that contain information on the sources, pathways, receptors and/or consequences for any of the top 40 trans-basin flood events in Germany (as presented in Uhlemann et al, 2010) that can be used as another source of data for flood research.…”