20 May 2022
20 May 2022
Status: a revised version of this preprint is currently under review for the journal NHESS.

A multi-disciplinary analysis of the exceptional flood event of July 2021 in central Europe. Part 1: Event description and analysis

Susanna Mohr1,2, Uwe Ehret1,3, Michael Kunz1,2, Patrick Ludwig1,2, Alberto Caldas-Alvarez2, James E. Daniell1,4, Florian Ehmele2, Hendrik Feldmann2, Mário J. Franca3, Christian Gattke5, Marie Hundhausen2, Peter Knippertz2, Katharina Küpfer1,2, Bernhard Mühr1, Joaquim G. Pinto1,2, Julian Quinting2, Andreas M. Schäfer1,6, Marc Scheibel7, Frank Seidel3, and Christina Wisotzky1,8 Susanna Mohr et al.
  • 1Center for Disaster Management and Risk Reduction Technology (CEDIM), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
  • 2Institute of Meteorology and Climate Research (IMK-TRO), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
  • 3Institute for Water and River Basin Management, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
  • 4Institute of Photogrammetry and Remote Sensing, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
  • 5Erftverband, Bergheim, Germany
  • 6Geophysical Institute, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
  • 7Wupperverband, Wuppertal, Germany
  • 8Institute of Economics, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany

Abstract. The July 2021 flood in central Europe was one of the five costliest natural disasters in Europe in the last half century with estimated total damage of EUR 32 billion. This study investigates the complex interactions between meteorological, hydrological, and hydro-morphological processes and mechanisms that led to the exceptional flood. Furthermore, we present our estimates of the impacts in terms of inundation areas, traffic disruptions, and economic losses. The estimation of inundation areas as well as the derived damage assessments were carried out during or directly after the flood, and show the potential of near-real-time forensic disaster analyses for crisis management, emergency personnel on-site, and the provision of relief supplies. The superposition of several factors resulted in widespread extreme precipitation totals and water levels well beyond a 100-year event: slow propagation of the low pressure system Bernd, convection embedded in a mesoscale precipitation field, unusually moist air masses associated with a significant positive anomaly in sea surface temperature over the Baltic Sea, wet soils, and steep terrain. Various hydro-morphodynamic processes as well as changes in valley morphology observed during the event exacerbated the impact of the flood. Relevant effects included, among many others, the occurrence of extreme landscape erosion, rapidly evolving erosion and scour processes in the channel network and urban space, recruitment of debris from the natural and urban landscape, deposition and clogging of bottlenecks in the channel network with eventual collapse. This study is part one of a two-paper series. The second part puts the July 2021 flood into a historical context and into the context of climate change.

Susanna Mohr et al.

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Susanna Mohr et al.

Susanna Mohr et al.


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Short summary
The flood event in July 2021 was one of the most severe natural disasters in Europe in the last half century. The objective of this two-part study is a multi-disciplinary assessment that examine the complex process interactions in different compartments, from meteorology to hydrological conditions to hydro-morphological processes to impacts on assets and environment. While Part 1 focuses on the description of the event, the second part puts the event in historical and climate change contexts.