the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 24 Jul 2024
Causes of the exceptionally high number of fatalities in the Ahr valley, Germany, during the 2021 flood
Abstract. Over the last 40 years (1980–2020), 159 people have died in inland floods in Germany. The flood of 2021 caused 190 flood fatalities in Germany, 134 of them in the Ahr valley. We investigate what made this event so 'deadly' in order to help improve flood risk management and prevent future fatalities. A comprehensive analysis of the factors influencing the occurrence of fatalities is carried out on the basis of the death investigation files of the public prosecutor's office. This unprecedented flash flood was characterised by high water levels and high flow velocities. The extent of inundation in 2021 far exceeded the official hazard map for the extreme flood scenario. Additionally, early warning and evacuation were inadequate so that many people were surprised by the flash flood. 75 % of the fatalities occurred outside of the mapped hazard zones. Particularly dangerous places were campsites, cellars and basement flats, but many people died on the ground floor (37 %) or outside on the street (18 %). The elderly above 60 years of age (78 %) and those with mobility or cognitive impairments (16 %) were particularly vulnerable. No gender-specific differences in vulnerability were observed. Public understanding of the particular danger posed by flash floods must be improved, as must the development and presentation of worst-case scenarios in hazard maps. Additionally, impact forecasting can significantly improve emergency management of such unprecedented floods. Specific recommendations are that in the event of such extreme flash floods, the warning messages must clearly communicate that saving human lives must be the priority, i.e., those at risk should move to safe places, e.g., to the upper floors. Evacuations must be initiated in good time, especially where flooding of the ground floor with high water levels is to be expected, paying particular attention to the safety of the elderly and people with limited mobility.
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Status: open (until 04 Sep 2024)
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RC1: 'Comment on egusphere-2024-2066', Katerina Papagiannaki, 29 Jul 2024
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Causes of the exceptionally high number of fatalities in the Ahr valley, Germany, during the 2021 flood
General comments
The aim of this paper fits perfectly with the aim and scope of the journal. It is about one of the most catastrophic floods in recent history in Europe, and its analysis is of high interest from many perspectives. The study of fatalities, circumstances and causes is critical. The article is very well-written and presents the results and recommendations clearly and concisely. I believe it merits being accepted for publication, and I only have some minor comments below.
Abstract
L39: ‘Specific recommendations are that in the event of such extreme flash floods, the warning messages must clearly communicate that saving human lives must be the priority,..’
Qu.: To whom will this message (that saving human lives must be the priority) be delivered? It sounds like a message to managers, not to the people. However, the specification in the same sentence (those at risk should move to safe places, e.g., to the upper floors’) sounds like targeting people. I think this should be a bit modified, as I assume that a message to the people would not include that saving human lives must be the priority.
Data and Methods
153: ‘In 19% of the cases, only the place of discovery is known’’
Qu.: Are these excluded from the analyses? Based on the results, yes; thus, I recommend clarifying this here.
154-155: ‘In these cases, the place of discovery was geocoded. In these cases, it is not clear if the accident had occurred outside or indoors and how close the place of discovery was to the location of the accident’
Qu: I suggest rephrasing or merging the 2 sentences, as to repeat the phrase ‘In these cases’ is not so nice.
How many are the uncertain location data?
Results and Discussion
165: ‘The probability of fatal accidents during floods increases with more severe hazard impacts’
178: ‘The combined hazard impact of water level multiplied by flow velocity is decisive for destabilising people standing in the flood water.’
Qu: I suppose the authors mean ‘hazard severity’ instead of 'hazard impact'. Even if the velocity and depth are consequences of the rainfall hazard, they are still considered associated hazards. The word ‘impact’ is a bit confusing, especially when the analysis focuses on flood-induced impacts, i.e. human fatalities.
196: ‘We therefore recommend improving the development and presentation of worst-case scenarios for official hazard maps and expanding the use of impact forecasting, as it can significantly improve emergency management of unprecedented floods’
Qu: Based on the previous comment, the impact forecasting here is unclear. Does it concern fatalities or water depth and velocities?
Citation: https://doi.org/10.5194/egusphere-2024-2066-RC1 -
RC2: 'Comment on egusphere-2024-2066', Karin M. de Bruijn, 30 Aug 2024
reply
Causes of the exceptionally high number of fatalities in the Ahr valley, Germany, during the 2021 flood
General comments
The paper explains the factors which made the flood event the deadliest one in Germany in more than 40 years by studying the circumstances and backgrounds of the individual fatality reports. The paper is well written, easy to read and clear.
The most important factors that contributed to the large number of fatalities in this event are:
- The extreme severity of the flooding with both high water levels and extremely high flow velocities.
- The underestimation of the hazard and its potential consequences:
- The underestimated flood forecasts 24 hours before the flooding,
- The lack of awareness at the governments and public of the possibility of these severe types of floods in this area and the potential to be life threatening.
- The ineffective warning: the warning which did not reach everybody and did not convey clearly the message that a life-threatning event might occur and that people needed to find a safe location.
- The incapacity to rescue oneself of elderly and people with a disability.
Some minor suggestions are provided below to enhance the discussion on the analysis of the factors contributing to the fatality numbers or to enhance the clarity of the paper even further.
Specific comments/minor suggestions
Abstract: The abstract is clearly written. It describes the events and demonstrates its extremity, it provides information on where people died and provides recommendations to reduce the probability of such disasters in the future. However, it does not summarize the causes of the high number of fatalities as is promised in the title. This might be added in a summarized form.
In the text and abstract the flood is sometimes referred to as unprecedented flood, but it is also explained that a similar event occurred in 1804. Perhaps one sentence can be added explaining this: the flood is called unprecedented, but this refers to the recent history. There was a similar flooding in 1804, but then the valley was still completely different and also the village was different and most people are not aware of this past flood anymore.
Add some context in section 3 if possible: The analysis focused of course on the fatality records. To get a complete insight into the occurrence of flood fatalities however, also locations without fatalities should be considered. This may be mentioned without adding such an analysis to this paper. The paper says that in more than 73% of the cases (flood fatalities) water depths exceeded 2m. Is there also info on e.g. how many residences experienced these conditions in total (with and without fatalities). Thus: did you also consider locations without fatalities with similar conditions and looked at how people there survived? Might that add to the understanding of why the other people died? What is the mortality of the event in total? Are the fatalities rare exceptions/incidents or did people at certain very dangerous locations had a seriously higher mortality than at other locations?
Line 174: you mention cellars as dangerous, but you indicate that water depths were above 4 meters so that many fatalities occurred on the ground floor. Do you know if many people died in cellars? If not, perhaps mention that. It is a little confusing now.
Line 275: This line suggests that the focus of emergency communication was on mitigating economic damage before. This was not explained before. What was the message? Give that more attention in the paper, since that may also be a contributing factor to why that many fatalities occurred.
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