SPIEGEL: Mr. Friedrich, is the next catastrophe in store for us this weekend?
Andreas Friedrich: New storms are coming, yes. Overall, however, we have a different general weather situation than during the floods caused by low »Bernd«. Several days of heavy rain and especially continuous rain came together with huge amounts of precipitation over a larger area, which then led to the crossing of rivers and streams and the violent floods. Now at the weekend we are expecting warm, humid air and a low, but unlike “Bernd” that will not settle over days, but will be driven by stronger air currents.
Andreas Friedrich studied meteorology and is press spokesman and tornado officer at the German Weather Service (DWD) in Offenbach.
SPIEGEL: What does that mean in concrete terms?
Friedrich: We get typical summer thunderstorms. There will be short-term and locally limited storms on Saturday in the southwest and on the edge of the Alps, which will spread northeastward in the evening and on Sunday night, i.e. also in the direction of Rhineland-Palatinate and North Rhine-Westphalia. It can also lead to hail, squalls and heavy rain with more than 40 liters of rain per square meter in one or two hours. The thunderstorms occur so locally that it will pour and thunderstorm in one place and the sun may already be shining again in the next.
“We can only say how much rain comes from the sky.”
SPIEGEL: According to recent experiences, alarm bells are ringing for many people when it comes to heavy rain. Right?
Friedrich: There is no need to panic, but storms should not be played down either. In Germany, warm and humid air can be expected well into the coming week and, accordingly, showers and thunderstorms again and again. We will continue to monitor the situation closely in the coming days and issue a short-term warning if necessary.
SPIEGEL: How does the average consumer know whether a severe weather warning threatens flooding with serious consequences?
Friedrich: This is difficult. Ultimately, it is about the question of how the expected precipitation will affect the water levels of rivers and streams. That goes beyond the responsibility of us meteorologists. We can only tell how much rain is coming from the sky. At least that provides a rough indication of the overall situation.
Friedrich: If you look at the weather maps on the website of the German Weather Service (DWD) or in the warning app before a storm, you can see how the purple-colored areas are distributed. These are the regions with the highest warning level, where thunderstorms and a lot of precipitation can be expected in a short time. The overview shows, for example, when thunderstorms only occur locally, i.e. maybe in two or three communities. Then no major flood disaster caused by tidal waves in rivers is to be expected.
“It makes a difference whether someone lives on a hill without a watercourse or in a valley near a small stream”
SPIEGEL: In the affected areas, however, a lot of water falls in a short time. What does a severe weather warning mean for municipalities?
Friedrich: Locally, heavy rain can cause landslides, smaller streams can overflow their banks, and basements can be flooded. What exactly happens, however, depends on the specific conditions on site.
SPIEGEL: Do you have an example?
Friedrich: It makes a difference whether someone lives on a hill with no watercourse or in a valley near a small stream, in which there can be a flash flood or, in extreme cases, a landslide. Whatever applies: basements should be avoided in such extreme weather situations. An overloaded sewerage system can fill them up even if there is no river or stream nearby. For all further measures you should pay attention to the local information provided by the emergency response teams. They will surely take a closer look now.
»Climate report« is the SPIEGEL podcast on the state of the planet.
We ask whether the ecological turnaround will succeed. Which political ideas and economic innovations are convincing. Every week we show what impact the climate crisis is having on our planet and why we are living in the most exciting decade of this century.
Apple Podcasts, Google Podcasts, RSS-Feed
SPIEGEL: What role does it play for the current risk assessment that it has recently rained a lot in North Rhine-Westphalia?
Friedrich: Again heavy rain would have negative effects there faster because the soil is already very saturated with water. New precipitation then seeps away poorly and runs above ground into streams or rivers. This is now less explosive than with the low »Bernd« because, as I said, it only happens very locally. With a view to the affected places, I don’t want to play down anything. There can be landslides, a small stream can overflow its banks and a mudslide can go through the village. We had pictures like this again and again in the past few weeks. However, we do not yet know whether there will be any more storms at all in the last affected regions at the weekend. If we’re lucky, the thunderstorms just pass.
“It won’t be much more specific until Saturday morning.”
SPIEGEL: When will it be clear where the thunderstorms are discharging?
Friedrich: It will probably only become much more specific on Saturday morning. Then we can narrow down the regions affected by the storm and the duration of the events more precisely and then also issue advance information. We know which exact locations will be affected and to what extent, unlike in the case of the low »Bernd«, but only 30 to 90 minutes beforehand. To do this, we have to briefly monitor storm cells on the radar.
SPIEGEL: In connection with the most recent flood disaster, there is currently much discussion about failure of civil protection. Should the German Weather Service have warned more clearly?
Friedrich: As a federal authority, we naturally discussed the issue. There will be numerous meetings in the coming weeks, also with the flood control centers of the federal states. They analyze on site, based on our precipitation forecasts, how the water levels of rivers will change. In contrast to the European flood warning system, which we read a lot about right now, they also determine the values for smaller rivers such as the Aar.
However, I cannot say what the problem is in the current case, because I do not know exactly how information was provided in the affected locations. But you have to realize that the flood was an event that is to be expected in the region much less frequently than every hundred years. Our climatologists have just analyzed that. This certainly contributed to the fact that the regions were not prepared for a flood of such magnitude.