The Ahrtal Bluff: How the Lauenburgische Landeszeitung Reverses Its Own 2023 Source

On 14 July 2023, the same publisher reported under the headline "Heat and Heavy Rain: How Dangerous It Will Be in Geesthacht" on exactly the study that had to serve again in 2026: the heavy rain modelling by the Climate Service Center Germany (GERICS, Helmholtz Centre Hereon) for the central urban area of Geesthacht.

GERICS researcher Markus Groth presented the findings personally at the Geesthacht Committee for Urban and Transport Planning, and the article quotes his conclusion verbatim: "Such flooding is not to be expected in Geesthacht's topography." Explicitly referring to flooding "like in the Ahrtal" — the comparison with the then 134 deaths and 80 billion euros in damage appears directly before this in the same article.

Note: in 2023, the same newspaper summarised the core statement of the responsible scientist as follows: an Ahrtal scenario is not to be expected for Geesthacht. In 2026, the same newspaper turned this exact study into a headline suggesting the opposite — without this context. This is not a matter of interpretation. This is a self-contradiction.

To prevent the accusation from hanging unanswered: in the GERICS study (City Series 04, February 2023, and the follow-up publication City Series 07, July 2025), "Ahrtal" is a scenario name for a quantity parameter.

The modelling uses the software HEC-RAS (free software by the US Army Corps of Engineers) to calculate surface water runoff after heavy rain for the central urban area. Scenario #1 uses a real recorded heavy rain event (Boizenburg/Elbe station, approximately 92.5 mm total precipitation, of which 51.6 mm in one hour). Scenario #2, named by GERICS itself "Extreme Heavy Rain (Heavy Rain of Ahrtal Type)", simply takes the rainfall amount of the Ahrtal event (162 mm in a few hours) and applies it to the Geesthacht terrain model.

This is a quantity transfer, not an event transfer. Nobody simulated "what happens if the Ahrtal flood comes to Geesthacht" — rather "what happens to surface water in Geesthacht if this rainfall amount falls." In 2026, the Lauenburgische Landeszeitung took the researchers' internal scenario name and built a headline with a death toll from it.

Even under the "Ahrtal rainfall amount", the result remains locally limited. The study identifies eight low-lying areas in the urban area where rainwater accumulates; under extreme conditions, four more are added. Several of these are wooded depressions which, according to the study, "are to be assessed as unproblematic on site" because the water seeps away harmlessly there or could serve as retention space.

The eight main areas: Düneberger Straße/Neuer Krug, the wooded depression north of Grenzstraße, Geesthachter Straße/Querweg, Sandstraße/Schillerstraße, Berliner Straße/Hansastraße, the Holtersche Kiesgrube, the area north of Dialogweg, and the Ostlandsiedlung. Water depths of up to two metres, in the extreme scenario locally up to 2.7 metres — but at individual, known locations, not across the board.

The explicit overall conclusion of the study: For the largest part of the modelled urban area, there is currently only a low risk of flooding after heavy rain events — and this also applies to extreme heavy rain events. This is the part of the GERICS project from which the "Ahrtal" comparison in the headline originates. It says the opposite of what the headline claims.

The study itself never calls itself an official expert report or a final hazard map. In the metadata and in the introduction it states in black and white: "prototypical product development", with the aim of showing smaller municipalities that even simplified digital models can be useful planning tools. This is not hidden — it is openly stated in the report.

And these simplifications are considerable. All buildings in Geesthacht were given a fictional standard height of 3 metres with a flat roof in the model, regardless of what the building actually looks like. The sewage system was completely removed from the calculation, because the researchers assume it will be immediately overloaded during heavy rain anyway. On page 29 they also openly admit that "rain retention by roof surfaces and vegetation [...] was not taken into account." And the digital terrain model (DGM1) does not know every road culvert, which is why the researchers repeatedly recommend checking each of the eight hot spots on site rather than relying on the map alone.

Here is the point that the Lauenburgische Landeszeitung completely missed: every single one of these simplifications points in the same direction. No sewage system, no roof retention, no vegetation holding water back, plus houses that only stand in the way as simple 3-metre blocks: the model has a built-in tendency to show MORE surface water than would be expected in reality, not less. If anything, it is biased towards worst-case.

And even this upwardly biased prototype reaches the conclusion: "low flood risk" for the majority of the city, even with Ahrtal rainfall amounts. This is not a study that underestimates the risk because it is too crude. It is rather too crude in the other direction — and still says: essentially uncritical overall.

One more point: HEC-RAS is actually a model for simulating river basins. True, but it was not used here to simulate the Elbe or a river — it was used to calculate rainwater on streets and in depressions. The tool can handle rivers; here it was about puddles growing larger, not a river overflowing its banks.

The question of the hot spots themselves remains: here the on-site inspection recommendation inverts. At the eight (or twelve) known problem spots, the model could actually be off — in both directions — because road culverts that drain water in reality may be missing from the model, or real bottlenecks may be absent. That is precisely why GERICS recommends checking each of these points individually rather than relying on the map alone. That is honest science. For the rest of the city — the part the headline is actually talking about — this changes nothing.

Even ignoring the study: the Ahrtal disaster was a river flood. The Ahr, a small river in a narrow gorge valley, rose by several metres within hours and tore houses away with enormous flow velocity. This precise combination — small watercourse, narrow valley, steep gradient, no drainage reserves — made the water masses into a lethal wave.

The GERICS modelling for Geesthacht describes something different: heavy rain surface runoff. Rainwater that accumulates in depressions over several hours; the "drainage phase" begins around one hour after the heaviest rain, and the entire process through to infiltration extends over up to 14 hours. The Elbe itself is deliberately removed from the calculation in the model, because it transports the water away rather than backing it up — the exact opposite of the Ahr.

To construct a comparable catastrophic risk from two small rivers with completely different topography and water flow is hydrologically untenable. And the time factor is decisive for the question "life-threatening or not": a flood wave arriving within minutes leaves no time to react. Water that accumulates over hours in a known depression does.

If one wants to deal in death tolls from climate scenarios: the same researcher, the same presentation in 2023, the same article: "Most deaths occur from heat." GERICS created, parallel to the heavy rain study, an urban climate modelling (PALM-4U) for Geesthacht that shows: surface temperatures of up to 60 degrees on sealed surfaces on summer days, strong to very strong heat stress (37 to 39 degrees) in almost the entire built-up urban area.

In other words: if the Lauenburgische Landeszeitung wanted to write a headline with fatalities and a climate change angle for Geesthacht actually supported by GERICS research, it should have written about heat, not flood. The death toll from the Ahrtal was attributed to the wrong risk.

None of this means that heavy rain in Geesthacht is not an issue. On 7 August 2024, cellars and streets were flooded after a storm, the Fährstraße was inundated, drain covers overflowed — the newspaper reported on this in September 2024 under the headline "How a Vehicle Should Protect Against Flooding After Heavy Rain."

But read what the 2024 article is actually about: "Geesthacht's drainage system is actually quite well equipped to handle rain floods" — the problem is blocked silt traps at gully drains. The solution being discussed in the building committee: a new cleaning vehicle for around 300,000 euros, plus more staff for the maintenance of the 26,000 inlet points in the 90-kilometre-long stormwater drainage network. This is infrastructure maintenance, a solvable, budgeted administrative issue. Not "could also cost people their lives here like in the Ahrtal."

The city and GERICS have already published a joint leaflet since October 2024 ("Heavy Rain and Flash Floods: Well Prepared, Better Protected") with specific precautionary tips for households in the identified risk areas: check backflow valves, do not store important documents in the basement, keep road inlets in the vicinity clean. Factual, undramatic, publicly available for two years.

A headline that had correctly reflected the real situation in Geesthacht might have read: "Heavy Rain: Twelve Known Problem Spots in Geesthacht, Heat Remains the Greater Risk." Not as punchy as "135 Dead", but supported by the underlying research — and by its own reporting from 2023.

Instead, in 2026 the Lauenburgische Landeszeitung took an internal scenario name from a study, linked it to the death toll of a real disaster, and thereby omitted exactly the context that its own reporter had received three years earlier from the same scientist:

"Not to be expected."

Anyone wanting to sell fear apparently does not need new material. The old material works too — you just have to leave out half of it.

Do your elderly relatives a favour: send them this text before the fear from the headline becomes the only information that sticks with them — not so that they stop worrying, but so that they worry about the right things.