The meteorologists cannot be blamed.

Several days before the flood disaster they had already warned urgently about heavy rain and floods, and two days before the rain, the calculations of high-resolution regional models agreed well with the actual amounts of precipitation.

Nevertheless, they too were later seen contrite: no meteorologist would have expected such a catastrophe.

Andreas Frey

Freelance writer in the science of the Frankfurter Allgemeine Sonntagszeitung.

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The problem was not her lack of imagination, but the difficult translation of the large-scale extreme weather event to individual regions and local conditions, i.e. to what the rain would do on the ground. And that's not a meteorologist's job. They tend to make general statements about possible dangers that the weather holds in store. These are officially stipulated in the various warning levels of the German Weather Service, which are passed on to authorities and municipalities, as in this case. The weather service had warned in good time of extreme risk of storms - and declared the highest warning level. But now it becomes clear at the latest: In order to warn of such catastrophic consequences as in the Ahr Valley, the usual forecasts and severe weather warnings are not sufficient,because 200 liters cause less on the flat land than in a narrow valley without a drain.

A heated debate has broken out about how people can be better protected in the future. Christian Kuhlicke from the Helmholtz Center for Environmental Research in Leipzig is researching such questions. A week ago, the geographer and risk researcher and colleagues published five principles for climate-safe municipalities, which should be used as a basis for future redevelopment of cities and municipalities. The scientists call for improved early warning systems and the strengthening of civil protection. This should succeed with a kind of damage prediction that analyzes certain parameters at a location in order to sound the alarm in good time in the event of an extreme weather event. Every community should know where their sensitive areas are.

For this "Impact Forecasting", which Kuhlicke presented in the

Reviews of Geophysics

last summer

, an exposure and risk analysis is required first.

All essential information must be collected on site in order to be appropriately prepared.

For floods and flash floods, high-resolution terrain models are required that contain information about buildings and vegetation and also take into account critical infrastructure such as hospitals or kindergartens, which must first be evacuated in an emergency.

This basis is connected with hydrological models of the flow behavior of streams and rivers as well as the runoff behavior of heavy rain and finally combined with the current weather data on total rain and soil moisture.

Learn from the Swiss

In the end, the local authorities have an early warning system at their disposal, with which they can reliably identify dangers and warn the population at an early stage. In order for the system to work, one not only has to understand the instructions, but also practice them regularly, says Kuhlicke, who experienced a paradoxical situation during the Elbe flood in 2002: people were warned in good time, but they believed that their place of residence would not be flooded. The more so, the better they thought they knew their river. Kuhlicke sees the canton of Bern as a model, where people have learned from the floods of the past that there is now an “excellent early warning system” with clear hazard warning levels. Every water level is linked to specific instructions, and when the water level is critical, people knowwhich road is impassable and where to evacuate.