Project Manager (PM) Yamaguchi Kosei and his colleague Nishijima Kazuyoshi who promotes the project are working on a project titled Heavy Rainfall Control for Living Together with Isolated-Convective Rainstorms and Line-Shaped Rainbands. PM Yamaguchi is studying the mechanism of how guerrilla heavy rains are formed and ways to control them, while Dr. Nishijima is measuring air flow patterns using a miniature town inside a wind tunnel in order to verify these control techniques. Science communicator and comedian Kuro Rabu Kyoju talks to them about their research, raising lots of questions. The discussion turns to how the project results will be implemented in future society. What do you think about a future where we live together with weather control?

《Click here for an article about the mechanism of how “guerrilla heavy rain” is formed and methods to control them》

Building the city of Kobe inside a wind tunnel

Kuro Rabu: Wow! I’ve never seen a wind tunnel before. It’s pretty big, isn’t it!

Nishijima: This wind tunnel is 50 metres long. It’s an experimental facility to generate air flows and investigate their effects. There are several types of wind tunnels; this one is a boundary layer wind tunnel. “Boundary layer” refers to the thin layer that forms between a solid and a fluid. A very thin boundary layer forms on the surface of a moving vehicle, for example. But the boundary layer between the solid Earth and the fluid atmosphere extends from the Earth’s surface to a height of around 500 or 1,000 metres. 
The fluid in the boundary layer increases in horizontal velocity as it gets higher above the surface of the solid, and at the same time the flow becomes turbulent, with vortices of various sizes. On the Earth where we live, weather phenomena occur inside this complex flow of air. That’s why we are conducting experiments in a boundary layer wind tunnel as part of this project. But it is not easy to artificially create a boundary layer, which is why the wind tunnel needs to be so long.

Kuro Rabu: So that’s the reason! How is the boundary layer created?

Nishijima: First, the fan at the end rotates to generate a flow of air. At first, there is turbulence from the edges of the fan, so the flow is expanded to pass through grids of different sizes to create a uniform flow. This reduces the velocity, so the flow is compressed. This requires a length of 25 metres.
Once the velocity of the uniform flow has been restored, turbulence is generated using blocks placed on the floor inside the wind tunnel. A length of over 10 metres is required to develop a boundary layer 1 metre in height, which means the last 5 metres can be used for experiments. I plan to place a model of the city of Kobe inside the wind tunnel to verify Dr. Yamaguchi’s simulations, such as how buildings trigger the formation of updrafts.

Kuro Rabu: Are you making the model town yourself?

Nishijima: The students in my laboratory are making it using 3D printers. In this field of building engineering, we often do experiments with model buildings inside the wind tunnel to test windproof design, but usually we just need a model of a single building, and the job of making models is outsourced. For these experiments for the Moonshot project, we had to figure out how to make a model of a whole city, which took over a year of trial and error.
We use 3D data about buildings from aerial surveys and so on. We have finally reached the stage where we have a routine processing method, allowing models to be made directly from the data. The buildings are laid out on the model city, divided into 15-cm square sections. In the past, it took almost a year to make one model city, but we will now be able to make many per year, allowing us to conduct experiments with various patterns.

Kuro Rabu: Now you have the know-how, right?

Nishijima: Yes. We are making other kinds of models, too. Let me show you the workshop.

Kuro Rabu: What are they making here?

Nishijima: I have asked the technicians to cut out the shape of a building from a block of aluminium using this machine tool, called a milling machine.

Kuro Rabu: A building made from aluminium? What will you use that for?

Nishijima: We will heat it and place it in the model city to recreate a building acting as a heat source. When it is heated with a Peltier element, the temperature of the whole model building will increase.

Kuro Rabu measures the temperature of an aluminium model of Kobe City Hall. The white device affixed to the model is a Peltier element, a flat semiconductor element which dissipates heat on one side and absorbs heat on the other side when a current flows through it.

Nishijima: The students are also making a model of a ventilation fan which can be placed near a building to dispel air vortices. Unlike a wind turbine, which rotates in the wind and absorb its energy, a ventilation fan is a device that uses power to produce wind. According to Dr. Yamaguchi’s theory, updrafts caused by warmth from the Earth’s surface and buildings trigger the growth of vortices which result in heavy rain. That’s why we are trying to use ventilation fans to eliminate the updrafts that cause these vortices.
The components of the fan are also being made using a 3D printer to ensure high accuracy. We are considering several different methods of controlling heavy rain. Another method is using wind turbines to suppress the wind blowing in from the sea, so we intend to make model wind turbines at some point, too.

Kuro Rabu confirms the rotation of the ventilation fan

Visualizing air flow with miniscule bubbles

Kuro Rabu: How do you decide the scale of the model?

Nishijima: Right now, we are working with a scale of 1:500. The simulation range of Kobe city is 2.5 kilometres square, so the model is 5 metres square. We will place the model in the downstream part of the wind tunnel where the boundary layer is developed. The boundary layer on the surface of the Earth is 500 to 1,000 metres high, and the wind tunnel can produce a boundary layer 1 metre high, which means the scale of 1:500 will be just right to allow experiments to be performed within the boundary layer.
One thing we have to be careful of is that with a scale model, you need to adjust the scale and physical quantities according to the laws of physics. For example, when heating a model building, we need to adjust the temperature to achieve a realistic ratio of the updraft velocity caused by the temperature difference to the velocity in the horizontal direction.

Kuro Rabu: Wow! Through working with Dr. Yamaguchi on this project, you are making models that have never been considered before in building engineering. It’s fantastic how the Moonshot program produces such innovative research.

Nishijima: I think we should conduct this R&D project with a three-way approach of observation, simulation, and scale model experiments in the wind tunnel. To improve the accuracy of the mathematical model (*1) used for simulation, we need to verify the simulation results against real-life observation data, but it is impossible to observe all the data in such detail. That’s where scale model experiments come in, to compensate for this. Unlike observations in a natural environment, we can control the conditions of scale model experiments to obtain high-quality data.
Also, Dr. Yamaguchi’s simulations divide the city into a 30-metre grid, but that is not very detailed when you think on the scale of a building. For example, if we want to investigate how a ventilation fan 5 metres in diameter would affect the air flow around a building, the only way is to conduct experiments. My role is to measure this data in the wind tunnel and pass it on to Dr. Yamaguchi.

Kuro Rabu: The three-way approach sounds powerful! What is the hardest aspect of scale model experiments?

Nishijima: So far, it was building the model, but going forward, it will be accurately measuring the flow of air in three dimensions to detect vortices.

Kuro Rabu: How do you measure the flow of air, which is invisible?

Nishijima: We use helium soap bubbles – bubbles of 0.3 mm in diameter, filled with helium – as tracers. By shining a strong light on them and taking pictures at fixed intervals, we can find out the movement speed of individual tracers. We have confirmed that measurement can be done with two-dimensional equipment using a laser, but we have not done three-dimensional measurements yet. We are planning to try using high-brightness LEDs. If 3D measurement succeeds, I think this will basically remove the bottleneck for experiments.

Kuro Rabu: Then you will be able to recreate the phenomena leading to guerrilla heavy rain inside the wind tunnel, and investigate how placing ventilation fans or wind turbines would change these phenomena.

Visualization of air flow. 2D measurement using helium soap bubbles, with a laser as a light source. The aim is to perform 3D measurement using high brightness LEDs (provided by PM Yamaguchi)

Kuro Rabu: I have asked Dr. Nishijima about the difficulties of scale model experiments. Dr. Yamaguchi, what is the hardest aspect of simulation?

Yamaguchi: In my case, it’s how to make the mathematical model more accurate. The aim of our R&D project is to reliably contain the seeds of guerrilla heavy rain while they are small, using as little energy as possible, but there is still a lot we don’t know about the phenomena of seed formation and growth itself. I believe there are many undiscovered factors that could be effective in containing guerrilla heavy rain that we are not aware of yet.
Therefore, as Dr. Nishijima said, we need to input what we find out from observations into the simulation, and verify the findings of simulations by experiments, to improve the accuracy of the mathematical model. When it comes to developing new control devices, it is important to take the approach of learning through trial and error with experiments and incorporating the findings into our simulations.

Calming heavy rain, but only to save lives

Kuro Rabu: Finally, could I ask about the ELSI (*2) of this project? I’m sure many people are hoping that this project will lead to the ability to weaken guerrilla heavy rain, but are there any arguments against it?

Yamaguchi: Yes, there are. Rainwater is a resource, so if we stop heavy rain every time, it will reduce that resource. Some people don’t want us to reduce rainfall.

Kuro Rabu: If it didn’t rain, it would certainly be a problem for farming and so on. I guess you have to consider the possibility that new issues like this could emerge, too.

Yamaguchi: Humans have countless connections with rain. Not just occupations like agriculture and fishing, but everyday connections like washing and umbrellas, or traditions like rituals and prayers for rain. Rain appears in literature and art; it is linked to our infrastructure and what we do in emergencies. Rain has a huge scope of impact, which means no method of controlling heavy rain will ever please everyone. That’s what makes it so important for society as a whole to face up to heavy rain and consider what choices to make.

Kuro Rabu: My speciality of science communication will be vital, won’t it. We need to develop a culture of how to confront the issue of heavy rain.

Yamaguchi: Exactly. The technology might not be accepted unless the culture changes. If it was supposed to rain but it does not rain, that’s one thing, but a scenario where weakening heavy rain in one place causes rain somewhere else, could be more of a problem.

Kuro Rabu: The people where the rain ends up falling might think “hold on, this isn’t right.”

Yamaguchi: I have thought about various ways of resolving this, and I believe the only argument that will convince everybody is that it will save lives from heavy rain. In order to save people’s lives from torrential rain in area A, it will rain in area B, where it was not supposed to rain. But the rain will not cause harm in area B. I think we all need to create a society where this is accepted on the grounds that it stops lives from being lost in area A.
 
A phrase that I cherish is the “bosom of nature”. This is a phrase from my teacher, Dr. Nakakita Eiichi (*3), which teaches us that unless humans have an awareness of “being allowed to live on Earth, borrowing from nature” then we will fall into the trap of prioritising technology. As this project expands, in future, it may become possible to turn heavy rain into clear skies. But just because we have the technology to do so, does that mean we should use it? I think the answer is “no”.
 
If we remember that we live in the bosom of nature and rain is a blessing from nature, then I believe all we are allowed to do is to make small changes to save lives. If nature is going to make it rain heavily, perhaps we should control it with the idea of praying to the gods of nature: “please weaken the rain, just a little.” We refer to this as “calming heavy rain”.

Kuro Rabu: It’s about respecting that nature has the stronger power, right? If it becomes possible to control the weather, humans will also be put to the test. What do we want to do with that ability? Do we want it to rain, or do we want good weather all the time?

Nishijima: What kind of weather we think is good at different times will vary from person to person. What I am worried about is that even if Dr. Yamaguchi thinks about it in a humble way as “living in the bosom of nature”, once we start using weather control technology, it might be used in all kinds of ways. At the stage when the feasibility is low, even if a technical paper is published, it can’t be put into practice at an individual level, so we don’t need to worry too much. But as we approach 2050 and it comes closer to becoming a reality, somebody might do it.

Yamaguchi: I think that is actually a good thing. This applies to all technologies, not just weather control technology: if the person who first comes up with an idea succeeds, many people will jump on the bandwagon and use it. Once they overcome the stage where unforeseen issues tend to crop up, then it could result in something even better. Technologies develop as different people use them. But what is important is that humans always take care with the technology.

Kuro Rabu: That is technology being implemented in society in the true sense, isn’t it.

Nishijima: There are similar issues with technologies like genetic modification and cloning. If anybody could genetically modify or clone humans, we would be in big trouble, so there are regulations. We can look at these other technologies as reference.

Yamaguchi: For weather control technology, too, I think legislation will eventually be created after much debate.

Kuro Rabu: What measures are you considering in terms of ELSI?

Yamaguchi: We are researching ELSI as part of this project. Basically, I think it comes down to how we can get many people involved. It’s no good just working on it in the laboratory; it’s important to get out into the local community and listen to what people have to say about the effects of weakening heavy rain. People living in rural areas have a deeper connection with the weather, through agriculture and culture, than people in urban areas. Even in a city, something like sprinkling water on all the streets of Tokyo at once would have some impact on the weather. If we can link such everyday actions with huge wind turbines for weather control, it might help people to understand that there are similarities and differences.

Kuro Rabu: It’s about getting people to think about the issues and fostering. That’s truly a culture, isn’t it.

Yamaguchi: As more people get involved, it will lead to a discussion about both the advantages and disadvantages of controlling the weather. Even if the debate results in choosing not to control the weather, that is fine.

Kuro Rabu: Even if that happens, once we have the technology, the day might come when weather control is possible.

Yamaguchi: Yes. I believe that humans are wise, so one day we will be able to find the right way to control the weather, putting the technologies developed in the Moonshot project to use.

Kuro Rabu: I’m glad we finished by talking about your determination. I have learned a lot from today’s discussion and visit. Thank you very much.

Written by Aoyama Seiko
Photos and videos: Oshima Takuya

Related information

■Moonshot Research and Development Program

■Moonshot Goal 8
Realization of a society safe from the threat of extreme winds and rains by controlling and modifying the weather by 2050.

■Goal 8 R&D Projects
Heavy Rainfall Control for Living Together with Isolated-Convective Rainstorms and Line-Shaped Rainbands
(Project Manager: Yamaguchi Kosei)