Weather is not climate, but it is changing noticeably due to climate change. More heat. More storms. More extreme weather events. Reliable forecasts are all the more important. Europe is already producing the world’s most accurate medium-term forecasts, says Stephan Bojinski in ntv’s “Climate Laboratory”. But soon they should be even better, more precise and faster. Because the weather expert will soon be able to observe the earth for the European Agency for Meteorological Satellites (EUMETSAT) with three brand new Meteosat satellites: The resolution is significantly better, and there are also completely new instruments such as a lightning detector, says Bojinski. “This is information that has not previously been available.”
ntv.de: The flood disaster in the Ahr Valley has just marked its first anniversary. In retrospect, there were many allegations that warnings about the storm and floods were not given in good time or not enough. When do you know if a storm is going to be severe?
Stephan Bojinski: Not every storm is the same. From a local warm thunderstorm in the Frankfurt area, you know about two or three hours in advance whether it will be a heavy hailstorm or not. Then there are other weather conditions, which are also referred to as storms, but which are much more complex. That was the case with the Ahr valley. The German Weather Service (DWD) had issued a warning for heavy rain in the region about two or three days earlier. That was not a classic warm thunderstorm, but a stationary rain area with very heavy rainfall.
How do meteorologists recognize such weather conditions? What does it look like on satellite images?
There are several factors involved in a severe thunderstorm or severe weather. Wind speeds are important for aviation. You also need this to assess whether trees could fall onto the road or rails. Hailstorms, a frequent phenomenon of severe thunderstorms, represent a greater or lesser danger, depending on the size of the hailstones. The rainfall itself, of course, too. In every country in Europe there are different threshold values ??from which one speaks of a storm.
And also different variables that are used to decide whether the population needs to be warned or not?
Right. Five centimeters of snow is a huge thing in Greece. Then everything collapses. You can no longer drive a car in Athens because there are no snow removal machines. In Helsinki, on the other hand, that wouldn’t be a big deal. The amount of precipitation to be expected in the Ahr valley was estimated quite well. The difficulty, however, was that there had already been quite a lot of precipitation in the weeks before, so that the soil was quite saturated and could no longer absorb much water. A lot of water from the sky simply shot down unhindered into the relatively narrow valley and contributed to this massive tidal wave on the Ahr.
You said “estimated”. How exactly can you calculate what the weather will be like?
The most important basis for forecasts is the weather model. Every weather service has a simulation running on the computer, with which the current state of the weather can be recorded as accurately as possible. For this you need these observation data. You tell the model that this is roughly the current status. Then, based on physics, it calculates a prediction of what could happen. What wind speeds you can expect or what amounts of rain. Of course, this is always associated with a certain degree of uncertainty.
How reliable are the predictions? Personally, one often has the impression that none of this is true at all.
It’s like other things: You’re more likely to notice what doesn’t work. In fact, rain forecasts are one of the most difficult things. Especially when only light precipitation is expected. Then to say whether it is actually drizzling a bit or not is complex. That depends on the flow conditions, whether enough moisture collects at a certain point, which then contributes to the formation of clouds and which can then rain down and so on. It’s also quite complicated to say how much and how hard it’s raining when you know it’s going to rain. We hope that our data from the new satellites will play a major role, because with them we can measure how and where the humidity is distributed in the atmosphere much more often and more precisely. This should help the models to limit errors and estimate them more accurately.
Do you have a number of how high the hit rate is these days?
It depends what for. Weather apps often give a percentage. This percentage is calculated from a model that is run 100 times. If it shows rain in 80 model runs, that doesn’t mean it rains 80 percent of the time, or 80 percent of the comparable days. Frankly, these percentages are misleading. I can’t give a single metric to break that down into.
However, modelers routinely compare their models and predictions with actual measured data to improve their models. All weather centers in the world do this, including the DWD. That is called model verification. There is also a kind of competition between the modelers, who meet regularly within the framework of the World Meteorological Organization (WMO) and feed in their data according to a defined protocol. Then you can compare how good the models are for certain weather conditions.
So there are, so to speak, Champions League models and less good ones?
You could say that. But it really depends on what you want to know. Some models are better at predicting snow or high wind speeds. This is more important in northern countries than in the Mediterranean. Other models are better at predicting a rain event.
And with the help of your new satellites and data, the weather forecasts should be significantly better in the future.
This is the new generation of Meteosat satellites that we will operate. The first will be launched from Kourou in French Guiana at the end of November. This is what our partners from the European Space Agency (ESA) are doing together with the private sector. Once the satellite is in orbit, we will operate it for the next ten years. This satellite houses an improved imaging spectrometer, which gives us images every ten minutes, and a lightning detector. The second satellite will be launched in early 2024. It has a so-called infrared sounder on board that can measure humidity and temperature structures. The third satellite will be launched in 2025 and will be identical to the first but will provide images every two and a half minutes.
We expect a significantly higher spatial and temporal resolution of the information from these satellites, which we then deliver to the weather centers. This is information that has not previously been available.
What does “spatial and temporal resolution” mean? Does that mean better image resolution?
Exactly. We currently operate ten satellites, not just weather satellites. The image data from it is already being used successfully everywhere. However, the technology floating in space now is roughly as it was in the late 1990s. With the new satellites we are talking about a spatial resolution of up to 500 meters above the equator. Because of the viewing angle, it is about 700 to 800 meters in Europe. That means we have independent information about clouds, humidity and other factors such as fire every 700 to 800 meters.
Is the jump in resolution a huge step up like that seen in cell phone cameras over the past 20 years?
It’s a big step, the resolution improves by a factor of about six. We believe that many weather phenomena can be seen much more precisely and much earlier with it. For example, whether a small heat source will grow into a real thunderstorm or not. With the new satellites, we are also in a much better position to detect relatively small fires and thus contribute to early warning.
Can you see this in real time or is it delayed?
The latency is around 15 minutes. This time is needed for the recording from space to the desk or as data in the computer model. This is the computer infrastructure that processes this data and which in turn distributes it to the users. But we try to be faster.
Why did people wait so long to launch satellites with the new technology?
At the end of November we will not only launch this imaging instrument into space, but also a completely new lightning detection instrument. This has really never happened before, but of course it took a lot of development time. The imaging instrument was also jointly developed by aerospace industries in Germany, France and some other countries. It just takes time until everyone agrees to build this satellite, distribute the orders, until the instruments are ready. Also because the costs are not insignificant.
Do you have an order of magnitude of the cost?
The entire third-generation Meteosat program cost around 3.2 billion euros. This includes the development and operation of the satellites over 20 years. That sounds like a lot. But if you extrapolate that and assume that every EU citizen benefits from better weather and climate forecasts, it’s a one-time fee of six euros per person.
Have weather forecasts generally become more difficult as a result of climate change?
That’s a good question. Because the atmosphere heats up more, there are more heat thunderstorms or thunderstorm fronts, especially in summer. These thunderstorms also become more intense and violent, that’s physics: When you have higher temperatures and more humidity, there is more potential energy that can translate into heavy rain or hailstorms. This does not make the individual prediction of these phenomena more difficult, but more frequent. We are prepared for this with the new satellites, because better forecasts allow us to know what is going to happen earlier and we can extend the warning time accordingly.
The announcement said that the quality of the weather forecast should be significantly better, but also that the flash flood in the Ahr Valley could not have been predicted better. What are the limits of the new satellites?
The prediction of many phenomena is significantly better because we can simply see things with the satellites that we cannot see at the moment. For example, there is currently no lightning location from space. The second satellite also uses the infrared sounder (IRS) to take pictures that we don’t yet have in this form: it collects information about the humidity and temperature structure of the atmosphere over Europe every half hour. However, there will always be weather conditions in which the satellites only have a small part in a direct forecast. For example, the IRS cannot see through clouds.
And the data is evaluated by people or does a computer do the work?
It goes hand in hand. As in other areas, there is also increased automation of the prediction process. Many weather services no longer allow a normal forecast to be made by a human being. She is only checked once more and then goes out. The advantage is that the forecasters then have more time to take care of difficult weather conditions and to analyze them more precisely. Of course, you also need research and development not only in EUMETSAT, but also in the weather services and universities to understand how we can best use the new data. It’s a learning process. It’s not going to be like launching the new instruments into space and then immediately understanding what the data can do for us.
How are we positioned in Europe?
The European Center for Medium Range Weather Forecasts (ECMWF) produces the most accurate forecasts in the world, we have the best medium range weather center in the world. This is not just a saying, but proven by these modeling competitions.
Die Champions League?
Exactly. But the other major services, especially in Great Britain and France, are also very far and are not much inferior to the model. Overall we have a very good R&D capability, but it could get even better now because we have so much innovation in space.
When will you start feeding the weather models with the great new data?
After the rocket launch in November, it takes a while for the satellite to reach its position. Then all sorts of tests take place, from the satellite itself, the control, the data reception and so on. That takes time. We expect about a year of testing until operational data comes out.
Clara Pfeffer and Christian Herrmann spoke to Stephan Bojinski. The conversation has been shortened and smoothed for better understanding.
