The Rainiest Place On Earth

Summary

The world's largest rainfall simulator in Japan creates extreme weather conditions to study flooding and landslides. With 550 nozzles, it simulates record 300mm/hour rainfall that occurred in Missouri. Tokyo's infrastructure prevents $1.7 billion in flood damage but 200 died in 2018 floods. The building moves to test shallow landslides on model terrain. Landslides increase with deforestation and climate change makes extreme rain more common. The simulator also tests drones and self-driving cars to improve their rain/visibility functionality. As climate impacts worsen, the importance of this research facility grows.

Takeaways

• 😲 The world's largest rainfall simulator in Japan can simulate rainfall intensities up to 300mm per hour, equal to the most intense rainfall ever recorded.
• 🌧️ The facility is used to study flooding and landslides, which are major natural disaster threats in Japan due to its climate and topology.
• 😮 The entire facility can move on railway tracks to test landslides on sloped sections recreating real-world conditions.
• ⛈️ Smaller raindrops fall slower than larger ones due to differences in their weight to surface area ratio affecting terminal velocity.
• 🚜 Deforestation has increased landslides 10x in some areas as tree roots provide stability and absorb water.
• 🔬 The complexity of landslide physics makes large scale physical simulations important for research.
• 🚗 Self-driving cars are tested at the facility to improve detection in heavy rain which can decrease sensor visibility.
• ☔ Catchment zones, diversion channels and drainage pipes help protect from landslide damage.
• 🌡️ Climate change is increasing extreme rainfall events, underscoring the importance of this research.
• 😠 Addressing root causes of climate change is ultimately more important than mitigating negative impacts.

Q & A

Why is the rainfall simulator so important for Japan?

The rainfall simulator helps scientists in Japan study flooding and landslides, which are major natural disaster threats in the country due to its mountainous terrain and frequent typhoons dumping heavy rain.

What is the intensity of rain that the rainfall simulator can produce?

The rainfall simulator can produce rain with an intensity between 15 mm per hour up to 300 mm per hour, which matches the highest rainfall intensity ever recorded of 305 mm per hour in Holt, Missouri in 1947.

How does rain contribute to landslides?

Rainwater fills the pores in soil, increasing water pressure between soil grains. This decreases friction holding the soil together, making slopes more likely to slide.

How have extreme rain events in Japan changed over the past 30 years?

Over the past 30 years, rain events in Japan with intensity over 50 mm/hr have become 40% more common, while events with over 100 mm/hr intensity are 70% more common.

What are some solutions for preventing landslides?

Solutions include steel beams/mesh to anchor slopes, lowering slope angles, drainage pipes, catchment zones to divert landslides, and planting trees since their roots anchor soil and draw up water.

Why does raindrop size matter for rainfall intensity?

Larger raindrops fall faster due to higher weight/surface area ratio. Smaller 1 mm drops fall ~2 m/s while 3 mm drops fall 6 m/s, so drop size affects rate rain accumulates.

How are self-driving cars tested at the rainfall simulator?

The simulator provides a repeatable environment to test how rain impacts the cameras and LIDAR sensors in self-driving cars used to detect objects, improving solutions to weather-related visibility issues.

What was the economic damage from floods during a 2018 typhoon?

Typhoon Prapiroon in 2018 caused over $10 billion USD in property damage across Japan due to flooding after parts of the country received 2 meters of rain in 10 days.

How can deforestation increase landslide risk?

Trees anchor soil with roots and absorb water. In British Columbia, deforestation led to a 10x increase in landslides due to lack of trees to stabilize soil.

How do tunnels and tanks help mitigate flooding in Tokyo?

Tunnels under Tokyo divert floodwaters from 100+ rivers into a huge underground water storage tank to prevent overflow that would otherwise damage the city of almost 40 million.

Outlines

00:00

😲 World's Largest Rainfall Simulator in Japan

Paragraph 1 introduces the world's largest rainfall simulator located in Tsukuba, Japan. It describes the facility that uses 550 nozzles to simulate rainfall from 15mm to 300mm per hour, the most intense rainfall ever recorded. The video host Derek sent producer Petr to experience the simulator.

05:00

🌧️ Studying Landslides and Preventing Damage

Paragraph 2 explains how the rainfall simulator building can move on tracks to create sloped landslide testing conditions up to 40 degrees. This allows scientists to study factors influencing landslides like soil type, minerals, and vegetation to help prevent damage through solutions like anchoring, drainage, diversion channels, and reforestation.

10:03

😔 Climate Change Increasing Extreme Rainfall

Paragraph 3 notes rainfall events with high intensity have become 40% more common compared to 30 years ago due to climate change, causing more flooding and landslides. It emphasizes the importance of addressing root causes of climate change, not just adapting to the impacts.

Keywords

💡rainfall

The amount of rain that falls over a given area and time period. Rainfall is a key concept in the video as the simulator is designed to replicate extreme amounts of rainfall to study flooding and landslides. For example, the facility can simulate the most rainfall ever measured in one hour - 305mm in Holt, Missouri in 1947.

💡landslide

The rapid downhill movement of soil, rock, or debris, often caused by heavy rainfall saturating the ground. Understanding and preventing landslides under extreme rainfall conditions is a major focus of research at the simulator.

💡typhoon

A tropical storm originating in the Pacific Ocean, like a hurricane, which brings very heavy rain as it moves over Japan and other countries. Typhoons dump huge volumes of rainfall which lead to flooding and landslides that the simulator helps study.

💡climate change

Long term changes in global weather patterns and average temperatures. Climate change is increasing the frequency and intensity of extreme rainfall events in Japan and around the world, which amplifies flooding and landslide risks over time.

💡flooding

The overflow or inundation of normally dry land areas with water. Extreme rainfall can cause dangerous flash flooding which leads to destruction of property and loss of life. The simulator studies flooding to help improve defenses.

💡velocity

The speed at which something moves. The video explains how raindrop size affects velocity - smaller drops fall slower due to more air resistance. This variable velocity is replicated in the simulator's sprinklers.

💡pore

A tiny space between particles of rock or soil. As rainfall seeps into pores it increases water pressure, reducing friction between particles, making the ground less stable on slopes and more likely to slide.

💡LIDAR

A laser scanning technology used in self-driving vehicles to detect surroundings. Testing LIDAR sensors at the facility helps improve their ability to see properly in heavy rain conditions.

💡aquifer

An underground layer of permeable rock or sediment that stores water. Deep drainage of water into aquifers is one way that trees help stabilize slopes and prevent landslides by lowering pore water pressure.

💡 anchors

Strong stabilizing structures like beams or mesh that secure slopes in place to avoid landslides. Anchors counteract the downward force of gravity to increase friction holding up the slope.

Highlights

The giant warehouse is equipped with 550 nozzles attached to the roof to simulate rainfall up to 300mm per hour, the most intense ever recorded.

Yakushima Island near Japan receives up to 10 meters of rain per year, 3 times more than the Amazon rainforest.

In July 2018, Japan had massive floods from Typhoon Prapiroon, forcing over 8 million evacuations. Damage exceeded $10 billion.

Tokyo's underground water storage system diverted 12 million cubic meters of water and prevented $1.7 billion in damage from a typhoon.

Japan has over 700,000 identified places at risk of dangerous landslides, which depend on many complex factors.

The rainfall simulator moves on rails to create slopes up to 40 degrees to study landslide causes and prevention.

Contrary to belief, water is not a lubricant for soil. It fills pores and increases pressure, reducing friction between grains.

Trees prevent landslides effectively. Their roots anchor soil, and they draw out and evaporate water, draining the soil.

In the past decades, deforestation has caused a 10-fold increase in landslides in the forests of British Columbia.

The simulator also tests drones and self-driving cars in rain and wind. Weather decreases sensor visibility and accuracy.

Due to climate change, rainfalls over 50mm/hour in Japan are 40% more common than 30 years ago. Over 100mm/hour is 70% more common.

The increasing extreme weather makes the rainfall simulator's work on flood and landslide prevention more vital than ever.

Simple prevention measures like slope anchoring, drainage pipes, catchment zones, and reforestation can mitigate landslide damage.

Humans trigger over 85% of landslides in Seattle through excavation, construction, and other environmental changes.

Future work should address climate change root causes instead of only mitigating the damage through engineering.

Transcripts

- [Derek] This is the world's largest rainfall simulator,

located in Tsukuba, Japan.

Now, I know that it just looks like a warehouse with a lot

of sprinklers, but this building is incredibly important.

The science conducted here keeps tens of millions

of people safe, and it's only becoming more and more vital.

We were given exclusive access to tour the facility,

and they even let us experience what it's like

to stand under the most intense rainfall

ever recorded.

- [Petr] This is insane.

Nope, nope, nope, nope, nope, nope, nope, nope.

- Japan is a land of natural disasters.

Most people will think of earthquakes, tsunamis,

and volcanoes, but it also experiences massive typhoons,

which are like hurricanes

that pick up energy from the Pacific Ocean

and dump meters of rain on the islands.

Yakushima Island near the southern part of Japan is one

of the wettest places on Earth,

receiving up to 10 meters of rain every year.

For comparison, the Amazon rainforest gets only

about three meters of rain per year.

That's three times less than Yakushima Island.

Most of the time, rain isn't a problem.

The water evaporates or seeps into the soil

and is then absorbed by plants

or enters the underground aquifer systems.

But too much rain in a short period,

like after a typhoon can lead to serious problems.

Problems that scientists working

at NIED use the rainfall simulator to study

and hopefully prevent.

The giant warehouse is equipped

with 550 nozzles attached to the roof.

The scientists can control the intensity

of the rain from 15 millimeters per hour

to 300 millimeters per hour.

The most rainfall ever measured in one hour occurred

on the 22nd of June, 1947, when 305 millimeters

of rain fell on the town of Holt, Missouri.

So this warehouse can simulate the most intense rainfall

anyone has ever experienced.

In a way that makes it the rainiest place on Earth.

And honestly, I'm having a good time here

in sunny Australia.

So I sent Veritasium producer Petr in my stead.

- They're gonna turn on the rain really soon.

So I'm running out to grab my rain jacket, I'm ready.

Wow, this is so much rain.

All around me, there is exactly 300 millimeters

of rain falling every hour.

We've only turned it on about five minutes ago,

and there's just so much rain.

There's already puddles, this is genuinely, absolutely wild.

I don't think I've ever experienced anything

like this before.

- The nozzles at the simulator contain four holes

of varying diameters, so they can produce raindrops

of different sizes, and the size of the raindrop affects

how fast it falls.

You've likely experienced the kind of rain

with the big droplets that pelt your face

or walked through a drizzle

where small drops hover like mist.

Because the smaller the raindrop, the slower it falls.

There are two forces that act on a raindrop,

gravity and air resistance.

And the larger raindrops have a higher weight

to surface area ratio,

and so they have a higher terminal velocity,

so they will be falling faster.

A raindrop that's one millimeter in diameter falls

at only about two meters per second,

while a three millimeter raindrop falls

at six meters per second.

Air resistance is also why raindrops aren't shaped

like cartoon raindrops.

They are closer to spherical,

but a bit flatter on the bottom

where they encounter oncoming air.

If a raindrop gets too big,

it flattens out, caves in in the middle

and briefly resembles a little parachute

before it breaks up into smaller droplets.

Flooding is something that Japan takes very seriously

and for good reason.

In July, 2018, there were floods all over the country

due to the rainfall from Typhoon Prapiroon.

Some regions of the country received nearly two meters

of rain in just 10 days,

and the resulting floods were enough

that more than 8 million people had

to be evacuated from their homes.

Over 200 people died,

and the damage to property from the flooding was more

than 1 trillion yen, nearly $10 billion.

Tokyo, the capital city of Japan,

is very vulnerable to flooding.

There are more than a hundred rivers crisscrossing the city

of nearly 40 million people.

To prevent the rivers from overflowing, there are pipes

and tunnels under the city leading

to an enormous water storage tank.

In October, 2019,

typhoon Hagibis dumped over 200 millimeters of rain

onto the city in under 48 hours.

The underground system diverted 12 million cubic meters

of water and prevented an estimated $1.7 billion in damage.

But flooding isn't the only problem.

Japan is a very mountainous country with many towns

and villages situated in valleys.

So combined with the heavy rainfall,

this creates the perfect conditions for another hazard.

(man screaming)

The researchers at NIED have identified over 700,000 places

where landslides are a significant threat to homes.

But landslides are so complicated.

There are so many factors

that affect if a landslide will occur,

how large it could be, how fast it will move,

and how much damage it will do.

Not just the slope angle or the amount of new rain,

but the type of soil, the minerals present,

and the vegetation growing on top of the slope.

This is footage from a landslide

that occurred in Norway in June of 2020.

There's barely any slope angle here,

but the whole area sits on a layer of quick clay,

an incredibly unstable clay layer, which when exposed

to intense rainfall loses its structural integrity,

becoming a liquid.

In the case of this landslide, there were no casualties,

though several homes were swept out to sea.

The complexity of the physics

of landslides is why the work done

at the large scale rainfall simulator is so important.

The best way to minimize landslide damage is prevention,

and it's the same for cybersecurity.

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backing up your data and updating your operating system

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of the video, and now back

to the world's largest rainfall simulator.

- All right, I'm gonna try it without an umbrella.

I have a very nice, very nice jacket.

I'm not sure how it's gonna hold up, but we're gonna try.

(Petr screaming)

Oh my God, this is insane.

Nope, nope, nope, nope, nope, nope, nope, nope.

My jacket is waterproof, so I was fine.

But my jeans are absolutely soaked through.

- [Derek] To study landslides,

the whole warehouse has a secret, it moves.

- [Peter] The rainfall simulator can be

in one of five positions.

- Velocity is about one meter per one minute.

- One meter per minute.

Wow, it moves on these railway tracks.

Every time you move it, you need

to grab this gigantic wrench and undo these bolts.

This is the pipe that connects

all the water up to the sprinklers.

There's a number of these kind

of openings in the pipe along the line.

So when you move it,

you just connect it to a different part.

So this is the landslide testing facility?

- Yes, this is a 30 degree slope, you can see this.

This is a shallow landslide.

Now you can put the soil here, about one meter.

- [Petr] You would put all the sand and all the soil,

and then you'd bring the building over.

You'd move it over here.

And then you'd start raining on it.

- Yes.

- [Dr. Sakai] 20 degrees this slope, is 20 degrees.

- Right, so you have a 30, a 40, and a 20,

20, 30, 40. - Yes.

- [Derek] So what causes landslides?

Well, a slope will slide when the force

of gravity pulling it down becomes greater

than the force of friction holding it up.

- There's a misnomer out there

that water makes the materials slipperier, so it rains

and it soaks into the ground and it makes it slipperier.

That's not true, water's actually an anti lubricant

for many materials, including quartz,

which is our most common mineral in soils and on earth.

- [Derek] So water doesn't make soil slipperier,

but soil is porous.

There are grains and there are pores between those grains.

And as it rains, the water seeps into the soil,

the pores become filled with water,

and as it keeps raining,

the water pressure in the pores increases,

which decreases the friction between the grains.

For a slope that was already at risk of sliding,

this decrease in friction is what ultimately leads

to the slope breaking apart and sliding downhill.

- One thing that our mathematical models are not

very well developed at yet is determining

is it going to slide slowly

or is it going to slide or maybe flow rapidly?

That's a tough one, that's, so experimentation's a great way

of getting at that.

And you know, the scaler effects are huge.

So many people have a little model in their lab,

you know, a small scale flume,

but now you're dealing with materials, you know,

you're starting to get off scale.

A large scale stimulation device like they have in Japan

is really important.

- [Derek] So how can you prevent landslides?

Well, there are a few things you can do,

like using steel beams and mesh to anchor the slope.

Or you can dig up the top layer of the soil

to decrease the slope angle.

And when it's expected that a slope will slide

after too much rain, engineers drill holes into the slope

and place pipes to drain the water out.

Another solution is to create catchment zones

and diversion channels, big holes in the ground

that will catch or divert the landslide

before it hits a residential area.

Trees are incredibly effective at preventing landslides.

Not only do their roots provide great anchors,

they draw the water up from the soil to be evaporated away,

which effectively drains the soil

and decreases the water level.

(chainsaw operating)

Where steep slopes have been deforested

for the timber industry, landslides have become more common.

Over the last few decades,

there has been a tenfold increase in landslides

in the forests of British Columbia.

- Humans are really good at causing landslides

and we're shaping the land a heck

of a lot more quickly than geologic processes do.

So when we excavate over here or add more weight

or more landslide or more material over here,

and that triggers landslides very, very regularly.

Study in Seattle from Seattle, Washington a few decades ago,

showed that I think more than 85%

had at least partial human trigger, if you will.

- [Derek] While the focus of the work is primarily

on landslide study and prevention,

the simulator is also used to test

how drones fly in rainy and windy conditions.

It's also used to test self-driving cars.

The data is used to improve the hardware

and software of how the cars detect various objects.

The two main ways that self-driving cars detect other cars,

traffic lights and pedestrians is with cameras

or LIDAR sensors.

In both cases, rain can decrease the visibility

and accuracy of these sensors.

So testing them in a perfectly repeatable environment

helps engineers develop solutions

to these weather challenges.

- In Japan, the rainfall condition is changing.

And now in this century,

the rainfall condition is so many heavy rainfall

in so much short time.

- [Derek] As the world heats up due to humanity's addiction

to fossil fuels,

extreme weather events are becoming more common.

Compared to 30 years ago, the number of rain events in Japan

with an intensity of 50 millimeters per hour

have become 40% more common.

Rainfall at double

that intensity has become 70% more common.

Climate change will increase the rate of flooding

and the occurrence of landslides in the future,

which is why the work done

at the world's largest rainfall simulator is becoming more

and more important.

But I hope that humanity focuses its efforts

on addressing the root causes of climate change

and not just on the mitigation of its negative impacts.