Floods are generally understood to be rising water in floodplains. With climate change, heavy rainfall events are increasing, which can cause damage not only to bodies of water, but generally to low points in the terrain where water collects.
Since the flooding in the Ahr valley and parts of North Rhine-Westphalia in summer 2021, everyone in Germany has been aware of the impact of major heavy rainfall events. With climate change and the warming of the atmosphere, heavy rainfall events will occur more frequently and more heavily than in previous decades. In principle, heavy rain can occur anywhere, which is why the city of Bad Homburg commissioned corresponding studies on the possible effects of heavy rain back in 2019. The results are presented here and available to all interested parties.
The flow path maps consider three scenarios:
Scenario 1 simulates a 100-year heavy rainfall event with 47.5 mm per square meter in one hour. The last time a comparable event occurred in Bad Homburg was in 2003. One millimetre of precipitation corresponds to one liter per square meter.
Scenario 2 simulates 80 mm of rain in one hour. Such an event occurred in Wiesbaden on May 27, 2016, for example, and comparable amounts of rain have also occurred in other places in Hesse in recent years.
Scenario 3 simulates 261.7 mm of rain in three hours. This is based on the largest measured rainfall event in Germany in recent decades, the heavy rainfall event in Münster on July 28, 2014. The precipitation in the Ahr Valley and in North Rhine-Westphalia in summer 2021 was around 200mm, showing that this dimension is no exception.
For the scenario calculation, a variety of bases were defined that were included in the calculations. In addition to a closely meshed elevation and building model, the existing sewer system, the water profiles, the actual land use, certain assumptions about the soil and other fundamentals were included. Due to the very large amount of data, simplified assumptions had to be made in some cases. For example, the heights of kerbs or the transverse inclination of roads could not be taken into account, or only to a very limited extent.
Nevertheless, the simulations provide detailed information on the flooding conditions, although deviations from these are still possible in detail. In addition to the flow paths, the scenarios provide graduated information on the water heights and flow velocities as well as the timing of the flooding in an extrapolation. The flow path maps are available both on the basis of aerial photographs and on the basis of parcel boundaries.
With these studies on heavy rainfall, the city of Bad Homburg v. d. Höhe has very helpful and easy-to-read simulations that show possible hazard areas. They are a very good basis for emergency planning by the fire department on the one hand and for further precautionary measures and precautions by the town and those who may be affected on the other.
Last year, and again this November in a specialist seminar, the city administration dealt with the findings on heavy rain and flooding across all departments. The fire department, urban drainage, energy suppliers and other important departments have been informed and can take these findings into account in their future planning.
In addition to the public protection and prevention approaches, every person who may be affected is also obliged to take precautions against the adverse consequences of flooding (in accordance with Section 5 of the Federal Water Act). This is why it is so important that you use the flow path maps for heavy rainfall to find out how you are personally affected and take appropriate precautionary measures yourself.
The information flyers and short videos from the German Association for Water, Wastewater and Waste (DWA), which can also be found on this website, can provide initial suggestions to help you help yourself. In addition, the city will be holding information events together with the fire department, other experts and local practitioners starting in spring 2022. The relevant dates can be found in the daily press and in the events calendar on this page.
The following page provides illustrative films on heavy rain precautions.
Responsibility for flood protection generally lies with the municipalities, which are responsible for local community affairs, urban land-use planning and hazard prevention. River basin-related, conceptual flood protection planning as the basis of functional services of general interest is carried out by the state. In addition, the state supports the municipalities in their projects by providing existing planning data.
Further information on current water levels and precipitation can be found on the website of the Hessian State Agency for Nature Conservation, Environment and Geology (HLNUG) under Floods / Floodplains
The town of Bad Homburg v. d. Höhe is a member of the German Association for Water, Wastewater and Waste (DWA) in Hennef.
The DWA has produced flyers on topics such as flooding and heavy rainfall (two of which are available from our citizens' office).
The following flyer explains the topic in text form. The DWA has made this flyer available in a read-only version
Further information, instructions and information on the subject can be found on the DWA website:
