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Flood risk in southwest Germany

In Germany, heavy flood events cause severe losses running into billions – as the events in 2002 and 2013 on the Elbe and Danube have shown. Based on an interdisciplinary research project between IMK-TRO, IWG and GPI, the risk of large-scale floods can now be estimated using a new developed approach.

The heaviest floods of recent years occurred in August 2002 and June 2013 along the Elbe and the Danube with a total loss of both events of around 22 billion €. Comparable floods in Baden-Württemberg along the Rhine and its tributaries occurred last in the early 1990s.

As part of the research project "FLORIS" (Flood Risk), the aim was to develop a flood risk model for the federal states of Baden-Württemberg, Hesse and Thuringia in order to better estimate the risk in these regions in the future. The work was carried out in cooperation with SV SparkassenVersicherung.

Since analyzes by Schröter et al. (2015) have shown that such events can be triggered by different meteorological and hydrological situations and conditions, the IMK-TRO first analyzed the meteorological conditions in advance and during severe floods and extrapolated them using statistical methods to create a comprehensive event catalog. For this purpose, a stochastic precipitation model (SPM; Ehmele, 2018, Ehmele and Kunz, 2018) was developed that generate high-resolution precipitation events (1 x 1 km²). Here, a simplified but still physically assignable approach to describe precipitation formation over mountains is used and supplemented by other terms describing precipitation formation by other physical processes. The solution via a Fourier transformation enables the simulation of many events in a short computing time. It turned out that the chosen method, although the simplifications, can simulate very realistic precipitation events and their spatial distributions (Figure 1).

Figure 1: Comparison of the strongest 200 precipitation events from observations (left, source: REGNIE, DWD) and 10,000 stochastically simulated events (right, SPM). Depicted is the precipitation field of the 90% percentile of the respective data set (Ehmele and Kunz, 2018).

On the basis of the event catalogs obtained, hydrological and hydraulic simulations were carried out by the Institute for Water and River Basin Management (IWG), from which the flood risk can be estimated by using new developed vulnerability curves (GPI).

More about this see the project page: http://www.imk-tro.kit.edu/5195_6248.php

Further references:

Ehmele, F. (2018): Stochastische Simulation großflächiger, hochwasserrelevanter Niederschlagsereignisse. Dissertation. Wissenschaftliche Berichte des Instituts für Meteorologie und Klimaforschung des Karlsruher Instituts für Technologie, Band 76, KIT Scientific Publishing, Karlsruhe, Deutschland. doi:10.5445/KSP/1000080495.

Ehmele, F. und M. Kunz (2018): Flood-Related Extreme Precipitation in Southwestern Germany: Development of a Two-Dimensional Stochastic Precipitation Model. Hydrol. Earth. Syst. Sci. Discuss., doi:10.5194/hess-2018-147, in review.

[Working group: Atmospheric Risks]