FloodsFlood Risks in Germany Were Clearly Underestimated

Published 11 August 2021

Expert say that to better estimate flood risks, risk maps should also consider historical data. The floods which devastated Rhineland-Palatinate and North Rhine-Westphalia caused 15 confirmed deaths, with more than two dozen people still unaccounted for. The damage is estimated at more than EUR 10 billion.

To better estimate flood risks, risk maps should also consider historical data. This is recommended by researchers at the Center for Disaster Management and Risk Reduction Technology (CEDIM) at Karlsruhe Institute of Technology (KIT). CEDIM has now presented its first report on the flood disaster in Rhineland-Palatinate and North Rhine-Westphalia. As regards the role of climate change, the combination of more water available in the atmosphere and increasing permanence of general weather situations is associated with an increasing probability of extreme precipitation events.

Last month’s flood disaster in Germany caused 157 confirmed death (more than two dozen people are still unaccounted for, and are presumed dead). Damage to buildings and infrastructure facilities can be estimated roughly only. It will amount to double-digit billions, including at least 2 billion euros for the transport infrastructures. Meanwhile, the German Insurance Association has estimated the insured loss to range from four to five billion euros in Rhineland-Palatinate and North Rhine-Westphalia only. How did it come to the floods that mainly hit Rhineland-Palatinate and North Rhine-Westphalia? How can flood risks – in particular rare and extreme events – be better estimated in advance? These questions were studied by the Forensic Disaster Analysis (FDA) Group of CEDIM that presented a first report.

The researchers explain that enormous precipitation volumes caused the Ahr river level (at Altenahr) to clearly exceed it previous record of 2016 (3.71 m, flow rate: 236 m3/s). As a result of the flood, the measurement station, however, broke down at a water level of 5.05 m (flow rate: 332 m3/s). From model calculations, the Rhineland-Palatinate State Agency for the Environment calculated a river level of up to seven meters in the night of the disaster. On this basis, experts estimated a flow rate that ranged between 400 and 700 m3/s. 

Several Factors Caused the Extremely High Precipitation
From the meteorological perspective, several factors caused the extremely high precipitation. “Within 48 hours, rainfall quantities in parts of North Rhine-Westphalia and Rhineland-Palatinate exceeded the total precipitation volume usually encountered in the month of July. Most of the precipitation even fell within about ten hours only,” CEDIM Spokesperson Professor Michael Kunz reports. In addition, the structured terrain of the regions affected, in particular in the district of Ahrweiler, with its deep river valleys increased surface flow. This situation was aggravated by the fact that the soil had already been saturated by high precipitation volumes on the previous days. 

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