-Very frightening moments unfolding in eastern Japan

along the Kinugawa River.

-Japan has been pounded with heavy rain

for two days in a row.

This is the 18th typhoon to hit Japan this year.

-September 2015.

20 inches of rain pelts down on Joso City

just outside Tokyo, Japan.

The river that flows through the city

can't contain this unprecedented rainfall.

The river floods, and 65,000 people

find themselves trapped in a watery nightmare.

♪♪♪

This, despite the fact that Tokyo has the most advanced

flood prevention system in the world.

-Japan is prone to so many different types

of natural disasters,

including the flooding and potential for mud slides

that we are seeing right now.

-But that system did not anticipate

the changes this century brings --

rising sea levels and stronger,

more frequent rainstorms than have ever been recorded.

-[ Speaking Japanese ]

-Tokyo's defense line is constructed to endure

a certain amount of rain.

The reality is the embankment

is not strong enough to withstand such force.

-[ Screams ] [ Helicopter blades whirring ]

-The world's great cities face threats

they have never before encountered.

New York.

Tokyo.

London.

Miami.

The threats come from the sea...

from above...

and from below.

These are the problems and their solutions...

♪♪♪

...for when the water comes.

♪♪♪

-More than 170,000 people received evacuation orders,

and we know dozens of them were stranded in their homes,

even a man holding onto a light pole

waving for the Japanese military helicopters

to come and rescue him.

-From June to October,

an average of 20 typhoons approach Japan each year.

But the typhoon that hit Joso City in September 2015

was different.

The area had seen stronger typhoons,

but never before had the rain fallen so hard.

[ Birds chirping ]

[ Door closes ]

-[ Speaking Japanese ]

♪♪♪

[ Speaking Japanese ]

-This is the Kinu River.

In Chinese letters, the name is spelled as angry demon.

-[ Speaking Japanese ]

-My father-in-law was also here.

He came with me because he was worried.

And as soon as he said, "Watch out!"

the water came rushing in.

-[ Speaking Japanese ]

-Hiromi Shinozaki and her father-in-law

were among the people swept away in the sudden deluge.

They clung to a floating piece of timber to avoid drowning.

Torrential waters washed everything away

in residential neighborhoods.

Hiromi was one of dozens of stranded residents

rescued by helicopters that day, as these people were.

-[ Speaking Japanese ]

-Holding onto the timber, we hoped that as long

as our faces were above the surface of the water,

we would be okay.

We held on as best we could.

But we weren't able to keep a hold on it,

so we had to swim for our lives.

-They finally made it to shore where they were still trapped.

♪♪♪

[ Announcement in Japanese over P.A. system ]

[ Siren wails ]

-[ Speaking Japanese ]

-People were stuck and needed help everywhere.

They were waving to helicopters, calling for help.

-[ Speaking Japanese ]

[ Helicopter blades whirring ]

-[ Speaking Japanese ]

-They were hovering above us.

One rescuer came down, but because of the fierce current,

he got washed away.

-[ Speaking Japanese ]

-I tried to hold on in spite of the strong wind.

It was really hard, but they finally pulled me up to safety.

-Her father in law was also rescued.

In fact, only two people died.

7,000 homes and buildings in Joso City

were damaged or destroyed in that flood.

Joso City was hit with 20 inches of rain in 24 hours.

If that much rain had fallen on Tokyo, just 30 miles away,

the results would have been even more catastrophic.

♪♪♪

Tokyo is the largest city in the world

with 38 million people in the Greater Tokyo Area.

Without this vital city, Japan's economy would collapse,

which is why protecting this city matters.

-Tokyo is like the Rolls-Royce of city and engineering.

It has most of the high tech system

that you can find in the world.

-Dr. Christopher Gomez of Kobe University studies

the threat Tokyo faces from the rising sea.

-Tokyo is the economic engine of Japan,

and Japan is one of the major engine of the world economy.

So all of this is interconnected.

If you start to have a major flood on Tokyo,

we're all going to pay it, and very directly, actually.

[ Birds crying ]

-[ Speaking Japanese ]

-Many insurance companies around the world,

such as Lloyd's or Swiss Re,

have assessed Tokyo

as the most dangerous city in the world.

And in their assessment,

they say Tokyo's preparation for flooding is not enough.

♪♪♪

-[ Speaking Japanese ]

-So the true risk to Tokyo lies in people believing

that they are protected and safe

when they are not at all.

♪♪♪

-Understanding Tokyo begins with a picture

of the city's relationship with the sea.

It sits on the shore of Tokyo Bay,

which connects to the Pacific Ocean.

To the city's East is the Edo River,

and its western border runs along the Tama River.

In all, 107 rivers run through the city.

Water is the heart and veins of Tokyo.

♪♪♪

Though some areas are below sea level,

the city sits 130 feet above it on average,

compared with New York at just over 30 feet

or Miami at 6 feet,

Tokyo's higher ground suggests relative safety

as oceans rise around the world.

But the difference with Tokyo

is the wide range of threats it faces --

more than any other city on the planet.

[ People scream ]

Earthquakes.

Tsunamis.

A unique quicksand phenomenon called liquefaction.

And, above all... [ Thunder rumbles ]

...powerful rainstorms that come with typhoons.

Typhoons pound Tokyo with rain from June to October every year.

The city gets 60 inches of rain per year,

three times the legendary rainfall of London.

But this isn't new.

♪♪♪

-32 inches of rain deluges heavily populated Kyushu,

Japan's southernmost major island.

Low-lying areas where cities and towns

are concentrated were hardest hit.

The record torrents brought

the island's streams and rivers to overflow,

a surging tide of destruction

swept through the area near Nagasaki,

leaving in its wake a sea of mud, debris, and death.

-In the half century since that 1954 deluge,

the heavy precipitation from these storms

has become 30 percent greater

and more intense than ever before

in the city's recorded history.

In 2018, typhoon Maria strikes Japan's southwest,

bringing the country's worst flooding and mudslides

in 35 years.

Millions of people are displaced from their homes,

throwing Japan into a state of emergency.

Over 200 people are dead,

and the damage is estimated in the billions of dollars

with roads, bridges, and railways destroyed.

The people of Japan reel from the disaster,

but fear worse is still to come

from even more powerful typhoons.

-[ Speaking Japanese ]

-The behavior of the typhoons around Japan in recent years

shows that they are clearly different

from the ones in the past.

-Dr. Tomoya Shibayama has been studying typhoons

and their rainfall for nearly 40 years.

-[ Speaking Japanese ]

-Until recently, it was common for a typhoon

to lose its intensity as it got closer to Japan

because the sea surface temperature was colder.

One of the recent changes is that typhoons

continue to grow as they approach Japan

because the sea surface temperature is warmer,

so the typhoon does not lose its power.

-Sea surface temperatures around Japan are expected

to rise by almost 4 degrees Fahrenheit by 2100.

This means storms will increase in intensity

as they approach the island nation.

-[ Speaking Japanese ]

-Until now, we have been referring to the Ise Bay Typhoon

as our benchmark.

-The Ise Bay Typhoon is also known as Typhoon Vera.

In 1959, it hit Japan with 20 inches of rain

and a 13-foot storm surge.

Some 5,000 people died, and Vera did

over $2 billion of damage --

Japan's deadliest and costliest typhoon.

-[ Speaking Japanese ]

-But in the future, I think we need to be prepared

for even bigger storm surges.

♪♪♪

-Flooding is a problem Tokyo has endured

for four centuries.

In the 20th Century after Typhoon Vera,

the city found solutions through elaborate engineering.

Water is diverted to rivers

through a series of canals and pipes,

which all flow back into the sea.

And the city's main rivers are contained by levees,

which have been built up over decades

to prevent flooding in low-lying areas.

-[ Speaking Japanese ]

-The limit of the Arakawa River's defense

is rainfall of 20 inches in 3 days.

The levees are built based on such a plan.

[ Helicopter blades whirring ]

So if the same kind of rain that fell on the Kinu River

would fall on Tokyo,

I have to say that the reality is,

the embankment is not strong enough to endure such force.

-[ Speaking Japanese ]

-Tokyo is defenseless against such rainfall.

-[ Speaking Japanese ]

-The moment the embankment breaks,

a high wave, like a tsunami, would hit residential areas.

♪♪♪

-Stronger, wetter typhoons are just one of Tokyo's problems.

Another is tsunamis, triggered by earthquakes.

Japan is situated on the Pacific Ring of Fire,

a tectonic plate that is responsible

for 90 percent of the world's earthquakes.

Japan records more of them every year

than any other country on earth -- 1,500 earthquakes.

With sea levels rising,

the aftershocks of tsunamis are deadlier than ever.

In 2011, an earthquake triggered a tsunami,

leading to meltdown

at the Fukushima Nuclear Power Plant.

The tsunami set off the worst

nuclear disaster since Chernobyl,

and it woke the world up to the constant danger Japan faces

from the sea.

-[ Speaking Japanese ]

-People realized that they had to recognize

the destructive power of the water.

If the river embankment in Tokyo breaks,

residential areas would be hit by waves

as large as the tsunami which destroyed Fukushima.

[ Helicopter blades whirring ]

♪♪♪

-The 2011 earthquake did impact Tokyo 150 miles away.

Yoshitaka Udagawa owns an exotic fish shop in Urayasu,

a city on Tokyo's outskirts.

-[ Speaking Japanese ]

-I felt a massive jolt with a giant thud.

We have many earthquakes in Japan,

so I thought, "It's an earthquake again."

But I had never experienced such an intense earthquake.

It continued, "Boom! Boom! Boom!"

-Udagawa fled his store,

into the street and the earthquake's fury.

♪♪♪

-[ Speaking Japanese ]

-It was difficult to walk.

The poles were really swaying in all directions.

The ground was shaking.

-[ Speaking Japanese ]

-I continued walking

and heard a noise when I got to this point.

You see that dark part over there?

There was something shooting out of it like oil blowing out.

-[ Speaking Japanese ]

♪♪♪

-The water's gushing out everywhere.

The ocean seems to be coming up.

-The dark liquid gushing from the ground was not oil,

but water and mud.

A process called liquefaction was causing the groundwater

to push up to the surface.

About 10 percent of Tokyo is built on low-lying sediment

along the city's coast.

The shaking effect from the earthquakes

creates a form of liquid earth, like quicksand.

Liquefaction is now a regular side effect

of earthquakes in Tokyo.

-Under your feet, you have up to 125 meters of soft sediment

mixed with water.

The problem with it is

that mixture between water and sediment,

each time you have a shake,

the water get expelled from the ground,

so it leaves hole in the ground in some ways,

and then the ground goes down.

♪♪♪

-Shinji Sassa of the Port and Airport Research Institute

created a shake table to demonstrate

the process of liquefaction in the laboratory.

♪♪♪

-3, 2, 1...

Okay.

[ Table whirring ]

-So when you look at the map right here,

you can see that all the blue areas here,

this is already below sea level.

We are minus one,

minus two meters below sea level.

And Tokyo is not any other city.

You have a major quake waiting for you,

so all of that can actually go down by an extra meter.

What you have to remember

is that all the sediments below the city,

a lot of them are a mixture of water and sand,

and once all this gets excited, you get liquefaction.

The water comes out,

and what remains is the land going down.

-Liquefaction is a new phenomenon in Tokyo.

It, too, is linked to the rising sea levels.

-The groundwater of Tokyo is connected to the sea level,

so if the sea level goes up,

then the groundwater will also go up.

It's like a pie chart -- we have been dividing that pie.

So those slices can be the river floods.

Another one can be

the liquefaction during an earthquake

that brings the land down.

Another one can be the storm surge.

Another one will be, again, the sea level rise.

And all of those elements that are looked on separately

will, at some point, happen together.

♪♪♪

-Tokyo has one last unique problem.

Entire neighborhoods are slowly sinking below sea level.

Decades of pumping ground water for domestic use

has left massive cavities below the city's foundations,

and some areas are now sinking.

-100 years ago, Tokyo was just a village,

just a few people, called Edo, actually.

And during the 19th Century, this village became the capital.

So on top of the marshlands,

on top of silty sediment mixed with water,

they started to drain this land and build this huge capital.

But it means that underneath the ground,

you still have the mud flats.

What you have below your feet is a mixture of water and sediment.

Until the 1960s,

people used to drink water from the ground water,

meaning that they pumped the water out of the ground.

So where the water was, then just a void remains.

So the land sinks slowly.

-30 percent of Tokyo's population

now lives below sea level,

and some homes have sunk as much as 15 feet due to subsidence,

the caving in of land.

As sea levels rise,

the gap between these low-lying neighborhoods

and the waters above them becomes ever more dangerous.

-[ Speaking Japanese ]

-The sea level rise is now producing the same effect

as the ground subsidence.

-[ Speaking Japanese ]

-The danger is getting greater and greater.

-[ Speaking Japanese ]

-You have a city which is just at the zero level,

so any increase in sea level is already a problem.

So this map here is the map of Tokyo.

So what you can see in the white here

is the bay where the water is,

and everything else is supposed to be land.

But if you look at it,

you can see that all the blue areas here --

and they are blue for a good reason.

It's because it's already below the sea level.

If you add 50 centimeters of sea level,

you can see that a large part of the city

already, in red here, is under water.

And then if you add 75 centimeters and one meter,

you almost have 100 square kilometers of water

covering your land.

-If the sea rises by 3 feet,

60 square miles of Tokyo will be submerged.

Japan's problems are compounded by an economic challenge.

Its population is expected to shrink by a third

in the next half-century.

In the past, a growing population and a booming economy

helped pay for megaprojects

to prevent and combat natural disasters.

Those days are ending.

40 percent of Japan's population

is projected to be over age 64 by 2050.

The country's birthrate is plummeting,

and it isn't expected to rebound to present levels

for another 45 years.

-So, Japan has been very good at facing its issue so far.

They've been working very hard on all of this.

You have a lot of engineering systems that are top notch.

But in a country where the population

is increasingly aging

and where money's going to be scarcer and scarcer,

how do you maintain all the system?

The population, which is aging, plus the climate change

is a real ticking bomb for Tokyo.

How do you build new dikes and new levees

when you don't have the fund for it?

So it's a real challenge.

-Kamaishi is 350 miles up the coast from Tokyo.

It's an extreme example of Japan's plummeting population.

Less than 40,000 people live here,

25,000 fewer than in 1980.

The city is home to the largest seawall in the world.

-[ Speaking Japanese ]

-The north wall was 3,200 feet.

The southern wall was 2,200 feet,

and the part where the ships go through was 1,000 feet long,

so as a whole,

it was 6,500 feet -- over a mile long.

-[ Speaking Japanese ]

-Kamaishi's breakwater is constructed

at a depth of 200 feet below the surface.

It's in the Guinness Book of World Records.

-The breakwater cost $1.6 billion

and took three decades to complete.

In 2009, the job was finally done.

[ Sirens wail ]

Just two years later...

-[ Shouts in Japanese ]

[ People scream ]

-...Japan's tsunami crushed this marvel of engineering like a toy

and swept through the town.

The bodies of about 1,000 people were never found.

[ Birds chirping ]

Akiko Iwasaki runs a hotel outside Kamaishi.

She witnessed the horrific 32-foot-high tidal flood

that destroyed her city.

She was also personally struck by tragedy.

One of her relatives was among those killed.

-[ Speaking Japanese ]

-One of my family members tied herself to a pillar

at the entrance of her house with a rope.

She was a senior, and when the firefighters

urged residents to evacuate, she probably didn't think

the tsunami would come up that high.

She didn't run away.

When she was found, her son said that,

in the time she took to tie herself to the pillar,

she could have run to safety.

♪♪♪

-[ Screams in Japanese ]

-Sadness turned to outrage.

How could this expensive megaproject

that was built to protect the city

fail so catastrophically?

The seawall is now being rebuilt.

And how to make it certain not to fail again

is Yussai Itoh's job.

-[ Speaking Japanese ]

-Since we're in the midst of construction,

we see some different heights.

However, they will be covered with concrete,

and they will all be level.

The tsunami came from offshore,

crossed the mouth of the bay breakwater,

and moved into the city.

It was about 33 feet high.

-[ Speaking Japanese ]

-The seawall had been designed to withstand

a wave of that height.

The engineers who designed the seawall

were determined to figure out why and how it failed

with such loss of life.

-[ Speaking Japanese ]

-Before the tsunami in Northeastern Japan,

we didn't understand exactly how barriers were destroyed.

♪♪♪

-In his hydraulics lab at Waseda University,

Dr. Tomoya Shibayama is trying to solve the mystery.

-[ Speaking Japanese ]

-This is the simulator for the waves

caused by the tsunami or the storm charge.

From the back of this waterway, the storm charge comes this way.

This structure here simulates the breakwaters.

The waves go beyond the breakwater

and reach the towns near Tokyo.

We observe how the water behaves in this area

using this hydraulic simulator.

♪♪♪

-Using the simulator to recreate a storm surge,

Shibayama and his research assistants

record it on a high-speed camera.

A colored dye allows them to see the water's behavior in detail.

-3, 2, 1, go.

-Once the experiment is complete,

Shibayama can look at the data collected by cameras and sensors

to determine the water's motion after it hits the barrier.

He concludes that the storm surge washed over the wall,

putting weight on the top,

and then dealt a vicious backwards blow

to the support structures underneath.

-It gets really fast here.

We must check the velocity field

and pressure field.

[ Metal clacks ]

-Once it gets past the breakwater,

powerful vortices push and pull

at the concrete in all directions

with a force the wall's designers did not anticipate.

Still, some experts believe

that even Japan's most advanced engineering

is no match for the increasing power of the sea.

-The hard solutions that people talk about --

various gates, levies, walls, and so forth,

I'm not sure it's practical

because sometimes, it's just not clear to me

that the science is there that says

it's really gonna do the job it's meant to do.

-Vishaan Chakrabarti is a New York architect

specializing in storm resilience.

-It's a basic Albert Einstein thing.

Matter doesn't just disappear.

The water just doesn't magically go away when you build a wall.

It gets redirected to someone else's doorstep,

and I think that's a fundamental issue that,

again, I can't solve as an architect.

I think most people who deal with this can't really solve.

-No wall is fail-safe.

So I think it does tend to encourage people

to live behind the wall in a way that's not resourceful,

in a way that trusts the wall to never fail.

And, uh, that's not good.

-Urban designer Kristina Hill warns against

what in her specialty are called "hard solutions."

The water always wins.

-When you build a wall, you size the foundation

for the height of the wall.

If you -- you can't just add more bricks to the top

and have it be structurally sound.

So future generations,

if that's not big enough, have to actually replace it.

-Dr. Shibayama also knows no seawall is invincible.

The revised plan is not to build higher or even stronger.

Rather than try to deflect the storm surge,

the new breakwater is designed to absorb its energy

and in extreme cases allow water to flow over top

without ripping it apart.

-[ Speaking Japanese ]

-The role of such hard structures as breakwaters

and tsunami storm surge walls isn't a complete defense,

rather, as with the case of Kamaishi,

they delay the storm's impact by reducing its energy.

-[ Speaking Japanese ]

-What we need to change moving forward

is that we are in the era in which each one of us

must think about how we are going to survive

and how we are going to protect our families

even if water goes over hard structures.

♪♪♪

-Typhoons, tsunamis, earthquakes,

rising seas, liquefaction, sinking neighborhoods.

Tokyo, the world's most populous city,

has the world's largest set of problems.

-So when you pile up all of those elements together --

so the sea level will rise one meter, plus the quake,

that's two meter.

Plus, eventually, a typhoon that can bring the water level

a meter higher, so that's three meters.

And if you are unlucky at that time

that you have flood from the rivers

or you have a small tsunami

that are predicted to be between 1 and 1.5 meter,

all piling those elements together,

well, you're in deep trouble.

It's not a question of is it going to happen.

It's a question of when it is going to happen.

♪♪♪

-Nonetheless, Tokyo may be one

of the very few cities in the world

seriously grappling with the challenge of climate change.

It's figured out engineering solutions before,

and with sea levels rising, Japan now needs to do it again.

In 1993, before climate change was much discussed,

Tokyo decided to tackle its existing flood problem

with a megaproject that many believe

was decades ahead of its time.

♪♪♪

♪♪♪

Japan built a futuristic cavern to protect itself against water

from above, below, or from the surrounding sea.

-[ Speaking Japanese ] -We are in the surge tank.

We have come down to 65 feet the ground.

On the left hand side is Shaft #1.

Further down the tunnel, we also have Shaft #2, 3,

4, and 5.

The overflow from flooding

is collected through these shafts

and goes through the tunnel

to come up through Shaft #1 gradually.

-[ Speaking Japanese ]

-The water then flows

into the Showa Drainage Pump Station

through this surge tank.

-[ Speaking Japanese ]

-When water floods Tokyo, this is where it all goes.

-[ Speaking Japanese ]

-The accumulated water will rise,

and eventually, it will reach a certain level.

Then, it gets forced through the four pumps

of the Showa Drainage Pump system

to be drained out to the Edo River.

-[ Speaking Japanese ]

-We have the water flowing into our facility

about seven times a year on average.

Out of those 7 times,

for about 60 percent of the time,

the water flows into here

and is forced out to the Edo River.

For the remaining 40 percent of the time,

we store the water here

as it can hold up to 670,000 tons,

and then the water gets returned to the river it came from.

-The system can hold up to 65 million gallons of water

and can pump it out as quickly as it comes in.

Lewis Makana is a UK-based engineer

focused on the problem of storm water management.

-For the mind's eye to capture the scale

and size of these silos,

you can take the Statue of Liberty

and place it inside one of those silos.

That's how big it is.

It's quite impressive.

Flooding in Tokyo is a big challenge.

If they didn't have that type of protection,

they would be gone.

♪♪♪

-[ Speaking Japanese ]

-It took 13 years to construct this facility --

from 1993 to 2006.

In actual figures, it cost 230 billion yen.

-That's more than $2 billion.

-Some domestic and international evaluations

consider this to be expensive.

However, the flood damages in this region

have been reduced to approximately one-tenth.

Therefore, I think it is not that expensive

when you take the flood damages into consideration.

-In 2015, after a record rainfall,

this temple to engineering was filled to the brim.

But the heaviest of those rains missed Tokyo,

with the greater impact outside the city to the northeast.

Kuniharu says the giant Showa Drainage Pump system

could not have coped if that storm had directly hit Tokyo.

-[ Speaking Japanese ]

-I heard it was the greatest amount of inflow and drainage

since this facility began its operation.

Our facility has four pumps,

and we usually use one or two at a time.

2015 was the first time all four pumps operated

at full capacity simultaneously for more than a week

to drain the water in an effort to mitigate

flooding in the region.

-Once the tank is full, it drains into the Edo River

at a rate of 53,000 gallons,

the capacity of an Olympic size swimming pool,

every 12 seconds.

It's the most advanced flood mitigation system on the planet.

But recent record rainfalls are too much

for even the massive reservoirs to handle.

-[ Speaking Japanese ]

-We do get questioned about what happens

if we had a rainfall of a similar scale,

and we must admit that we are not fully certain.

To build a facility in the first place,

there is an expected amount of water that will flow into it.

This facility was designed to cope with that amount.

But if there is a rainfall or water flow

that is above this upper limit,

we will not be able to take it in nor drain it out.

It is unavoidable that the local communities

will pay the price in such a case.

-With increased rainfall and rising seas,

engineers like Dr. Makana believe

the facility is no longer 100 percent effective.

-Even with this amazing superstructure,

they still recognize that because of climate change,

because of the rising sea level, and because of the potential,

using scenario modeling

and looking at the worst-case scenario

of what potentially could be the worst-case type of tide,

tidal surge, in addition to maybe a typhoon event,

they recognize this protection that is currently in place

will not be fit for purpose.

That will be something for them to discuss and feature

in their future planning for Tokyo,

but it will need to be put in place,

or else Tokyo will be submerged by flooding.

[ Water sloshes ]

♪♪♪

-Tokyo is protected by a series of 44 flood gates

along the city's many rivers.

They are designed to stop storm surges as high as 26 feet.

The highest ever recorded in Tokyo is only 10 feet.

♪♪♪

-[ Speaking Japanese ]

-In the event of tsunamis or storm surges,

we are supposed to close the gate

when the water reaches a certain level.

-Even with sea level rise,

the floodgates offer substantial protection

to over a quarter of Tokyo.

-[ Speaking Japanese ]

-You see that there are seawalls all around the gate,

and the walls look high.

But inside the walls, it's actually fairly low.

So if we don't close the gate,

the area inside the walls would be submerged.

-If the water overflows the riverbanks,

pumping stations are activated.

-[ Speaking Japanese ]

-When the water level on the inner side

of a closed water gate rises with rain,

you use this pump to move the water

accumulated inside the gate to the other side of the gate.

-[ Speaking Japanese

♪♪♪

-The next line of defense

is what's called super levees,

which are currently being built all around Tokyo.

Dr. Kristina Hill believes the levees are Japan's

best long-term solution against the rising sea.

-What they did was they piled up

all this earthquake-safe material,

so that means carefully sorted gravels and sands,

um, and then they extended everybody's property lines

up into the air through that new material,

and gave the original property owners

rights to redevelop buildings on top

that now have water views in some cases.

So I think it's a fantastic idea.

Even if the dike is overtopped, if water comes over the top,

they've built terraces on the backside

that should slow that water down

as it moved towards highly populated areas in Tokyo.

So important to slow flooding down.

-Nobuyuki Tsuchiya is lead engineer

on the super levee project.

-[ Speaking Japanese ]

-With the ground subsidence,

we had to reinforce the levees by adding height.

That's why this one looks a bit steep.

When it was originally made, it was more gradual.

Because we added the height, it's a bit unbalanced.

-[ Speaking Japanese ]

Because it's such a serious problem,

we've been working on this super levee project,

which would make this residential ground

as high as the levees

and defend the community from water.

-[ Speaking Japanese ]

-The super levees were planned to run

for 540 miles along 6 rivers to a height of 30 feet.

But that plan was so expensive, it was scaled down to protect

only the most vulnerable, low-lying areas.

Still, it comes at a cost to Tokyo's landscape

and for residents who have to leave their homes

as their entire neighborhoods are elevated.

-And then we fill the land and raise the ground level.

Then we build roads, parks,

and rebuild the town from scratch.

Then the residents can come back.

♪♪♪

-The people of Tokyo have come to realize

that they have few good options.

It's either evacuate for a short time for rebuilding

or abandon their homes for good.

-It's going to be challenging, but if this levee breaks,

it's not only these houses that get destroyed,

but also the water would overrun the whole Tokyo area.

If you think about that, then asking for some cooperation

and time from the residents here

would make the most sense for the safety of Tokyo.

-[ Speaking Japanese ]

♪♪♪

[ Siren wails ]

♪♪♪

[ Birds crying ]

-Tokyo has to seek a whole array of solutions

and keep re-engineering itself

for a future of rising seas.

-So the coastal defenses in Tokyo

are some of best in the world

by a long range.

And Tokyo City has been rising up their differences

to meet those challenges.

Does it mean that it's going to be enough

for the future challenges?

That's another question.

-The city may have to consider ideas from outside of Japan.

Kunlé Adeyemi is an architect whose focus is on building

near, and even on, water.

Faced with climate change, he believes

humanity has to adapt its thinking before it's too late.

-I am a realistic optimist.

[ Laughs ]

And what I mean by that

is that I'm realistic in the sense that,

you know, I go to Tokyo,

and I see the impact of sea level rise,

climate change, or simply water.

I just see places that used to be land

are now covered by water.

That is the real fact.

I don't want to see that as a problem.

I want to see that as an opportunity.

And how do I deal with this opportunity

where I have to learn to live with water

as opposed to fighting it?

And that's what I see --

we're producing infrastructure for water culture.

-Adeyemi has proposed an experimental design

for temporary, low-cost floating habitats

that can be used for housing, office space, or schools.

-Well, so, the idea is that we're trying to create

a building system

where the components are easy to fabricate

in any kind of local region

and assemble.

No matter where you are in the world,

you can find a particular class of timber

that will be suitable for the production of the structure.

-Adeyemi's design has been considered for several cities,

including Tokyo.

It can easily be adapted to Tokyo's unique environment.

Temperatures rarely drop below freezing,

and the structure can be made

to ride out heavy rains and waves.

-We've used two systems so far,

the first being just very basic, recycled plastic barrels

that are used in industrial areas

and second, has been uh, the expanded polystyrene,

which is used in construction.

We know there are different technologies

for creating floatation devices

that would enable this to work in different parts of the world.

♪♪♪

-Engineer Toshio Nakajima has an even more ambitious idea.

He's proposed an entire floating city in Tokyo Bay.

-[ Speaking Japanese ]

-The concept of this floating city

is to make the lowest land as safe as possible.

So we dig it out to make the low land even lower,

and then we flood it.

After putting the water in,

we build the floating foundation,

and we live on it so that when it rains

and the water level goes up,

the city itself is raised with the water

and protects itself from water disasters.

-Nakajima based his design on the Mega-Float --

a floating airplane runway in Tokyo Bay --

that has proven to be very effective.

Nakajima's city would use the same technology,

basically a gigantic modular floating dock.

-[ Speaking Japanese ]

-This water is taken from the Arakawa River,

and the water goes through the city

and goes out into the sea.

So the city controls the water.

-[ Speaking Japanese ]

-The energy we need to move the water through the city

is generated in this area here by using the solar panels.

-[ Speaking Japanese ]

-We would have a big tank underwater,

located below the city, to store rainwater, too.

-[ Speaking Japanese ]

-We won't need anything difficult technology-wise.

If we're serious about it, we can build it anytime.

-Nakajima's floating city would look

something like this video simulation.

It would be able to withstand sea level rise, storm surges,

and extreme rainfall.

But Tokyo's cash-strapped government

has not approved the plan so far.

-I think it's not only Tokyo, but in all of Japan,

people want to keep their conventional ways.

-[ Speaking Japanese ]

-I have the impression that many people are conservative

and not open to new ideas.

-Tokyo has to survive the rising waters.

The future of Japan depends on it.

Yet that may mean reshaping the city

by retreating from the areas in the greatest danger.

-One of the cheapest solution and one of the easiest solution,

at least on paper, might be the retreat

from the most floodable areas of Tokyo.

[ Thunder rumbles ]

-By the end of the century,

Tokyo's world-famous Shibuya district

could be one place to be abandoned to the waters.

-We're going to see the population shrinking,

so less people in the city.

And that's maybe a chance

to remodel the city in which we live.

How can we concentrate people in safe areas

and abandon slowly and naturally

areas that are too dangerous to live in?

-I think the question's not just about

whether we retreat or we stand our ground

because that sets this opposition

between humanity and the environment.

It's a reconsideration

of how to ensure that there's coexistence.

So there needs to be a balance,

and I think where we've always created walls

between us and the environment,

now we need to let go of the walls

and find new ways of bridging the gap.

-Some believe solutions may be rediscovered from history.

"Resiliency" is now a buzzword

of climate change engineering and design.

But it perfectly describes what the people of Tokyo

have been doing for centuries.

-[ Speaking Japanese ]

-Our ancestors made the city here on a low, flat land,

good for agriculture, and developed the city.

-[ Speaking Japanese ]

♪♪♪

-People learned to live with the water

when there was flooding.

It's like a city in the water.

In order to live there,

people made their residence higher.

We call it constructing a "Mizuya" or "Mizuka,"

a shelter from the flood.

But when you go to work, you go on a boat.

-[ Speaking Japanese ]

-When the water recedes, you just hang your boat

under the floor of your house.

So people lived flexibly with the water.

It was not about fighting the risk,

but predicting it, accepting it, and living with it.

-Tokyo is facing a huge amount of challenges,

but people are still here, rising to those challenges.

And the way they look at it, human beings are part of nature,

part of the environment.

Those hazards and disasters

also part of the environment we live in,

and we have to be able to live with it.

-Those who lived through

the most recent disasters to strike Tokyo

are still adapting to their changing world,

but they know they face challenges

previous generations never did.

-[ Speaking Japanese ]

-It's over there.

This is the manhole that popped out of the ground.

It's left as a monument.

This is it.

♪♪♪

It got pushed up out of the ground.

It reminds me that this happened,

and it makes me think

that we don't want something like this again.

My view now is that this is a place to pray

for no more disasters.

-Despite his prayers, sea levels continue to rise,

typhoons grow stronger, and it rains more than ever.

-[ Speaking Japanese ] -Yes.

I'm worried so much that I can't sleep.

That's why at this moment, too, we're trying to defend the city

as much as possible against the water.

-[ Speaking Japanese ]

-We're building super levees, strengthening seawalls,

improving pumping stations, and so on.

-Human beings need to see danger.

They need to know the world they live in

in order to become more resourceful over time.

We have a long haul here with climate change.

It's not going to be over in 50 years.

We need multiple generations

to become courageous and resourceful

and smart with their money and technology

and care about each other.

-With today's level of funding, today's engineering,

there is no clear answer

on how to engineer our way out of this problem.

But we're thinking about 50 years',

100 years' time from now.

And the engineering systems are going to progress, as well.

Nobody can tell what kind of solution

we're going to be able to create or build in 100 years.

-I would definitely say it is the Godzilla of all problems,

and I believe a lot of the problems we are facing

from climate change will require engineering-led solutions,

and whether an engineer can take on Godzilla

is what we are trying to find out.

[ Laughs ]

-It scares the bejesus out of me.

Living near the water, I think,

is something that is so core to the human spirit.

And even people who don't live near the oceans,

they go to lakes, they go to rivers.

I think this is just --

we come from water as a species.

And so I just... To me, it's just so tragic,

the idea that we now have to think of water as the enemy.

What we have right now is we have a tool kit

that can help us make things better in the short term.

That's only going to buy us some time

as we figure out this problem on a global level,

but it's at the global level that it has to be figured out.

-Engineers, planners, and civic leaders in Tokyo

are addressing their epic challenge

with technology, engineering, and imagination --

seeking solutions to protect the city for decades to come.

-[ Speaking Japanese ]

-Tokyo is trying to keep the water away

because it's being conventional.

They're trying to fight against the water.

But we can't keep doing that

because the water is something more powerful than us.

There's no way we would win.

-The more we learn to evolve and adapt

to what seems to be,

at least in the next 50, 100 years, the path,

the better we are in creating more livable environments.

And I think the human species

is an incredibly intelligent species,

and Tokyo will learn to live with water.

-[ Speaking Japanese ]

-Even though we have been trying our best,

I don't think we can say

that we are fully prepared for disasters.

♪♪♪

-Next time on "Sinking Cities,"

London has been plagued by flooding for centuries.

-London probably has one of the longest

flood histories of anywhere in the world.

-They built the Thames Barrier

and believed flooding was a thing of the past.

Now a city that thought it was safe

is facing a new reality --

sea levels are going up.

-A thousand properties got flooded

not from the tides, but the sky.

-You could get such a severe weather event,

it could overwhelm our defenses.

[ Indistinct conversations ]

♪♪♪

-To order "Sinking Cities" on DVD,

visit ShopPBS or call 1-800-PLAY-PBS.

This program is also available on Amazon Prime Video.

♪♪♪

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