Superfloods (2025)

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♪

NARRATOR: September .

Torrential rain hits North Carolina,

triggering flash floods that surge down valleys...

MAN: Holy...

NARRATOR: ...and destroy buildings.

MAN: It just ripped it in half.

TRISHA PALMER: Nobody in this part of the country

has ever seen anything like this before.

It was devastating.

[thunder rumbling]

NARRATOR: One month later, in Spain,

a massive flood hits Valencia.

ANDRIES KLARENBERG: Everything was flooded with three feet of water,

which was pushing cars

down the streets, into buildings.

MAN [speaking Spanish]:

NARRATOR: The flood kills more than people.

HANNAH CLOKE: Something went wrong in this flood.

We know that the flood forecasting and warning system

didn't work as it should have done.

NARRATOR: Then in Central Texas,

on the of July ...

...deadly floods k*ll over people.

[rushing water]

Are flash floods becoming more frequent?

MAN [speaking Spanish]:

NARRATOR: And more devastating?

There was a cascading

and compounding effect of this storm

which I fear is a harbinger of things to come.

NARRATOR: What can we do to protect ourselves

from these deadly inundations?

MAN [speaking Spanish]:

NARRATOR: "Superfloods,"

right now on "NOVA."

♪

ANNOUNCER: Major funding for "NOVA" is provided by the following:

♪

NARRATOR: On the of July

, an intense thunderstorm

in central Texas generates floods that k*ll

more than people, including

at least children.

It's the deadliest inland flooding

in the United States

in nearly half a century.

But this shocking disaster isn't an isolated event.

In the preceding months,

two other record-breaking storms

also produced devastating floods:

one in North Carolina,

the other in Europe.

Altogether, the three storms leave over people dead.

What can we learn from these disasters

to better protect us in the future?

[woman shouting in Spanish]

♪

Asheville, North Carolina.

It's a popular tourist destination.

Around million people visit the city every year

to enjoy its vibrant arts and culture...

...historic buildings...

...and spectacular mountain scenery.

Asheville's location,

over miles from the coast and , feet

up in the Blue Ridge Mountains

puts it far from the storm surges of Atlantic hurricanes.

Which made many people think

it was relatively safe from extreme weather.

[fishing line whizzing]

But that all changed in the autumn of .

♪

Wednesday, September .

Torrential rain pummels North Carolina,

and it looks like it's about to get worse.

For eight days,

meteorologists have been monitoring a weather system

coming in from the Gulf.

PALMER: By midday Monday, we had what we call

a potential tropical cyclone.

Nothing is actually formed, but something is going to form.

And already then we were talking about

significant heavy rainfall.

NARRATOR: By Wednesday morning,

the tropical cyclone has been named Helene

and grown into a hurricane.

Its predicted track puts it on a course

toward western North Carolina-- and Asheville.

The city sits at the junction of two rivers:

the French Broad and the Swannanoa.

On Wednesday afternoon,

the National Weather Service issues

a worrying forecast.

PALMER: We had a river forecast,

and our hydrologist put in there

the potential for "ruinous flooding"

along the French Broad and Swannanoa rivers.

He put in there this has the potential to be

"once-in-a-lifetime" flooding.

"Consider relocating" if you live

along the French Broad and Swannanoa Rivers.

We were very concerned, and quite frankly,

getting very scared at that point.

NARRATOR: But the trouble starts even before Hurricane Helene

reaches North Carolina.

On Thursday afternoon,

the eye of Helene is still miles away in the Gulf,

but in Asheville, after two days of heavy rain,

the French Broad River is already beginning to flood.

That night, at :, Helene makes landfall

on the Florida coast as a category storm.

Through the night, it tracks north,

and in the early hours of Friday morning,

dumps more rain onto Asheville and the surrounding mountains.

Eight miles east of Asheville lies the town of Swannanoa,

named after the river that flows through it.

On Friday morning, the overnight rain from Helene

swells the river, and it rises rapidly.

Michael Burgin is at home with his partner and year-old son,

when water starts flooding their street.

BURGIN: It was around : in the morning,

I did get an alert on my phone saying to evacuate.

At that time,

the water was about halfway up our cars outside.

So evacuating didn't seem possible.

Our idea was to go up to the attic first.

NARRATOR: But the water continues to rise.

BURGIN: We were up in the attic for a while.

The water started sloshing into the attic a little bit,

and we didn't want to get trapped.

So, we decided to swim down

into our kitchen.

NARRATOR: With water nearly up to the ceiling,

they try to escape through the windows.

BURGIN: We were going up and getting air

and then swimming down

and trying to get the windows open.

And neither one of them would budge.

And then eventually my son was able to break the window open.

We swam through the window and then got up on our roof.

♪

NARRATOR: miles downstream, the floodwater flowing down

the Swannanoa, reaches Asheville.

♪

CHRIS FABER: I was on a corner unit that basically

looked right up the river.

Early afternoon,

mid-afternoon is when it, it started rising a lot faster.

When it started to flood the first floor apartments,

everybody on the second floor was like,

"Oh man, like, that's crazy."

And then it hit the second floor.

[on camera]: Oh, my god!

[voiceover]: It kept coming and kept coming.

At first it was just random debris, you know,

litter, trash, or some tires,

street signs.

By : or so,

we started to see box trucks,

and shipping containers, and really quite large stuff.

♪

We could see these things coming a ways away,

and it just felt like slow motion.

It literally folded a giant shipping container,

like tin foil.

It just wrapped around it. Unbelievable.

It was pretty terrifying because everything looked like

it was going to hit us, and then kind of last minute,

it would whoosh its way out into the river.

[on camera]: Oh, come on baby, miss us.

[voiceover]: Certainly, the scariest one was seeing

entire buildings coming down the river.

NARRATOR: This isn't just a roof;

this is the entire Asheville Tea Company building.

WOMAN: It didn't hit us.

FABER: Holy...

...it just ripped it in half.

♪

NARRATOR: Upstream, in Swannanoa, floodwater continues

to pour through Michael's neighborhood.

BURGIN: We were on the roof for a total

of about three hours.

We started hearing foundations cracking,

It was very surreal and very scary.

NARRATOR: Eventually, neighbors in kayaks

carry Michael and his family to safety.

In the mid-afternoon,

the flood reaches its peak.

All along the Swannanoa river,

it has devastated communities.

On the morning of Saturday,

September , the people of western

North Carolina wake up to scenes of devastation.

FABER: It looked like a b*mb had gone off.

I mean the destruction is incredible.

Overturned cars stacked on top of each other.

Incredible depth of just mud

that you had to kind of really

work your way to get through.

Streets that were just ripped up.

It completely changed the landscape.

NARRATOR: On Michael's street, everything is filled with mud.

BURGIN: The water went down remarkably fast.

Most things were destroyed, obviously.

It just was really upsetting.

NARRATOR: The flash floods smashed through buildings,

swept away vehicles, and destroyed roads

and bridges.

In the hills, the rain

triggered landslides that buried homes and cut off roads.

As the search begins for the missing,

people want to know:

why did this happen here and now?

This was not the first time Asheville flooded.

In July , the tail end

of a hurricane hit western North Carolina,

followed by another hurricane

nine days later dumping heavy rain on the city.

The resulting flood k*lled about people.

It became known

as the Great Flood of .

Despite its mountain location far from the coast,

Asheville's geography actually makes it vulnerable to floods.

Parts of the city run along valleys,

close to the French Broad and Swannanoa rivers...

...and the mountains around the town help generate rain.

PALMER: Western North Carolina, upstate South Carolina,

it's got a unique feature called the Blue Ridge Escarpment.

The terrain rises very rapidly.

So you have this air that's being lifted up against

the Blue Ridge Escarpment and as the warm air rises,

it condenses and it starts raining,

and it just all starts

routing down from this creek to this creek to this creek.

Eventually, the larger streams start rising.

And this is where they live.

NARRATOR: This landscape helped create the Great Flood of .

But the flood of was even worse.

In Asheville, the Swannanoa River peaked over five feet

higher than the level reached in .

PALMER: Nobody in this part of the country

that's alive has ever seen anything like this before.

It was devastating.

NARRATOR: So why was this flood so extreme?

A clue comes in the form of another disaster.

On the other side of the Atlantic.

Just a month after the floods in North Carolina,

a deadly storm hit Valencia in Spain.

Like Asheville, Valencia is a popular

tourist destination... but the landscape here

is different.

The city sits between low-lying mountains and the sea.

Rain is rare.

The ravines that run

through the nearby towns are usually dry.

But when big storms occur, they have been known to flood.

October , .

Meteorologists across Europe

are growing concerned about

an approaching weather system.

This was going to be an extreme event.

This was going to be dangerous, this was going

to be something that was going to have a high impact

for the people in the region.

By the morning of Tuesday the of October,

a red warning had been issued at about : A.M.

Red warnings mean that there is a danger to life.

♪

NARRATOR: On Valencia's coast, a strong wind whips up

the Mediterranean sea,

but there's hardly any rain.

However, inland, heavy rain is falling

in the hills, and collecting in valleys.

Just south of Valencia, a ravine,

called the Rambla del Poyo,

runs from the mountains toward the Mediterranean.

Over half a dozen communities,

including the town of Paiporta, line its banks.

More are dotted in the surrounding flood plain.

Over , people live along the ravine.

♪

Shortly after : P.M. local time,

water flowing down the Rambla del Poyo

reaches the town of Paiporta.

It carries a wave of debris.

Within a few minutes, the dry ravine

becomes a powerful, fast-flowing river.

In the afternoon, the rain in the hills intensifies rapidly.

BENTLEY: During the height of the storm,

one location recorded millimeters of rain,

which is about two and a half feet of rainfall,

falling over a space of hours.

NARRATOR: Shortly after : P.M.,

flash flooding engulfs a town near the top of the ravine.

At : P.M., in Paiporta,

the river overflows its banks and rapidly floods the streets.

KLARENBERG: All the neighbors,

in the entire area,

started bringing their cars up out of the underground parking.

That was very strange.

NARRATOR: Residents here know what will happen

if the river floods basements.

[horns honking]

In towns along

the river's banks,

they race to save their cars.

KLARENBERG: There was a lot of noise. People shouting.

Every spare meter

of pavement, courtyard,

grass was filled with the cars from the neighborhood.

DANIEL BURGUET [speaking Spanish]:

NARRATOR: The storm that devastated the communities

around the Valencia region was unprecedented,

breaking the record for the most rain to fall in Spain

during a hour period.

[thunder rumbling]

What caused so much rain to fall in such a short time?

The answer is a weather system

meteorologists call a "cut-off low."

A cut-off low can form when an area of cold,

low pressure air gets cut off from the flow of the jet stream.

This high altitude rotating mass of low-pressure air

can draw in moist air from below.

The fact that they are cut off

from the main flow in the atmosphere

means that they sit in one location

and pump moisture into the same region

for several hours to days, even up to a week.

NARRATOR: When cut-off lows interact with a plentiful supply of moist air,

such as a warm ocean, they can become dangerous.

That summer,

the Mediterranean sea reached record high temperatures.

SHEPHERD: You have cold air in this cut-off low,

but the Mediterranean waters are quite warm.

That leads to a very unstable atmosphere

that can produce rising air,

condensation, and a lot of rainfall ultimately.

NARRATOR: Beneath the cut-off low, warm, moist air at the surface

rises rapidly, drawing in more warm air,

full of water vapor, from the Mediterranean.

This rapid uplift generates huge thunderstorms.

[lightning strikes, thunder rumbling]

SHEPHERD: When you have sustained moisture flow

and the dynamics associated

with a cut-off low, that leads oftentimes to extreme rainfall.

NARRATOR: In North Carolina,

the heavy rain that pummeled Asheville

in the days before Hurricane Helene arrived

was also caused, in part,

by a cut-off low.

SHEPHERD: The convergence of many factors produced a rainfall machine.

One of the factors

with this particular case was a cut-off low.

The way that low was situated,

it allowed moisture to flow into parts of Georgia

and North Carolina essentially creating a funnel

of moisture feeding these rain storms.

♪

NARRATOR: While Hurricane Helene was developing in the Gulf,

the cut-off low formed over Western Tennessee.

This low-pressure system sucked in air,

laden with water vapor, from the Gulf and Atlantic.

As this rose over the Blue Ridge mountains,

it triggered thunderstorms and torrential rain.

Meteorologists call this a predecessor rain event.

PALMER: A predecessor rainfall event is when you have rainfall

that is distinctly separate from the tropical system,

but it involves moisture that is being pulled up

from the tropical system,

so it saturates the ground ahead of the storm.

And so by the time the storm gets there,

everything is set up for a disaster.

NARRATOR: On Wednesday and Thursday, before Helene arrived,

the cut-off low brought heavy rain into North Carolina.

By Thursday afternoon, when Helene was

still miles away in the Gulf,

the French Broad River in Asheville

was already flooding.

But then the cut-off low did something else that helped

turn a moderate flood into a disaster.

When Hurricane Helene made landfall,

the winds spiraling around the cut-off low

pulled the storm toward it.

Downgraded to a tropical storm,

Helene barreled into the Blue Ridge Mountains

and dropped even more rain onto Asheville

and the surrounding area.

PALMER: In portions of the Black Mountains, we had

seven to ten inches of rain leading up to Helene,

and then we had over a foot of rain with Helene.

And as it just keeps raining, keeps raining, keeps raining...

...again, it just set up for,

for just a horrific, horrific event.

NARRATOR: The extreme rainfall in North Carolina, Valencia,

and Texas, and the floods that followed,

had devastating consequences for people and property.

Three historically devastating floods in the space of a year.

Just a coincidence? Or is a new pattern emerging?

SHEPHERD: We know that all across the United States,

the rate at which rain falls is more intense.

And that's related to a basic physics understanding.

As the atmosphere warms, there's more water vapor

available to the storms.

[thunder rumbling]

NARRATOR: For every degree Fahrenheit

that the atmosphere warms, the air can hold

% to % more water vapor.

Since pre-industrial times,

our atmosphere has warmed about

two degrees, so it can absorb about

% more water vapor than it used to.

This means that, in some storms,

heavy rain will be more intense than in the past.

Rising sea temperatures

can also add more water vapor to the atmosphere

because water evaporates faster at higher temperatures.

SHEPHERD: There is certainly

a relationship between warming water temperatures,

perhaps in the Mediterranean or the Gulf,

and the intensity and amount of rainfall in cut-off lows.

NARRATOR: The warm water in the Gulf provided the energy

that raised Helene to a category hurricane.

Hurricanes get their fuel from the oceans,

and that's a warm ocean.

And one of the things that we're increasingly seeing

is warm sea surface temperatures;

marine heat waves.

And so, these storms are stronger as they're moving in

and they're producing greater amounts of rainfall.

NARRATOR: In July ,

high levels of water vapor in the atmosphere above Texas

contributed to America's deadliest inland flood

in nearly half a century.

Warm, moist air from the Gulf moved

over central Texas, feeding powerful thunderstorms

that soaked the western Hill Country with heavy rain.

Floods swept down the Guadalupe River

and surrounding creeks,

leaving death and destruction behind.

SHEPHERD: The Texas floods were a combination of several

meteorological or weather factors.

That region is known as Flash Flood Alley.

It's close to the Gulf, and there was ample moisture

from the Gulf-- a quite warm Gulf by the way--

and you had the remnants of Tropical Storm Barry

that also was a moisture source.

As meteorologists, we look for moisture

as a signature of potential flooding.

And moisture was at record levels.

It was certainly clear to forecasters

that this was going to be a flood event.

NARRATOR: In Texas,

many weather stations reported five to ten inches of rain

in less than six hours.

When that rain funneled into the Guadalupe River,

it rose about feet in minutes.

The result was utter devastation.

[wood snapping]

The Texas and other recent floods

may be a sign of things to come.

Recent studies indicate that, as global temperatures rise,

the United States will see

an overall increase in flooding;

especially in the east.

And there's another problem.

As the world's population grows,

more people are living in areas that flood.

We've got a lot of pressure

to build new houses all of the time,

and that, of course,

makes it very difficult

to protect those places such as floodplains,

where we don't really want people living,

because they can be dangerous.

Sometimes floods don't happen for, you know,

a hundred years at a time,

so people will build,

because they think that there-- you know,

there's nothing that's going to happen.

But actually, it is a dangerous place.

NARRATOR: It's a double threat.

To stay safe, it's increasingly important

for people to be aware of the risks.

[buzzing]

But the range of danger

that floods and heavy rain present

depends a lot on the terrain.

[drone continues buzzing]

In the hills and mountains around Asheville,

the biggest k*ller from Helene was landslides.

The National Oceanic and Atmospheric Administration

classified the landslide deaths here

as fatalities from fresh water flooding.

PHILIP PRINCE: With this type of landsliding,

what we saw with Helene, water is the key ingredient.

None of what we saw happen is going to happen

without a tremendous amount of water present in the soil.

[water surging]

NARRATOR: Water from Helene caused this slide.

Fortunately, no one was hurt.

♪

PRINCE: It's absolutely the most acutely dangerous natural event

that you see in the Appalachian Mountains,

just because of the speed with which it moves.

NARRATOR: miles east of Asheville,

the storm left another tragedy in its wake.

In the small community of Craigtown,

people lost their lives

when a series of landslides swept down the mountain,

destroying homes.

Geologists Jennifer Bauer and Philip Prince

are helping compile an inventory

of the more than , landslides in North Carolina

triggered by Helene's rain.

Today, they are climbing to the top

of one of the Craigtown landslides

to find out what started it.

Can you see anywhere

that might be a ground water source up here?

Let's look under here.

NARRATOR: This slide, like most in North Carolina,

was a type of landslide known as a debris flow--

a landslide made of soil, rock, other objects, and water.

So this is what, like, I don't know,

three feet long?

That's a good way to concentrate

a lot of ground water in one spot.

Yeah. For sure.

NARRATOR: Debris flows often begin near the top of a mountain,

where the slopes are steepest.

Rain soaking into the soil can accumulate as groundwater

high on the mountain.

Underground channels can then funnel it to one spot.

This is a big hole in the ground

that groundwater just comes out of,

and groundwater can find its pathways

through all of the loose boulders in the soil.

And probably shot out through the soil right here.

PRINCE: And with the added push

from that providing almost, like, groundwater pressure

underneath the ground surface,

it's going to destabilize the type of soil we have here.

NARRATOR: The saturated soil here triggered a debris flow

that traveled about a mile and a half

before it hit Craigtown.

At approximately miles an hour,

that would only take about three and a half minutes.

Residents would have had little warning of what was coming.

Across the southeast, landslides were

one of Hurricane Helene's biggest K*llers.

So, what can people do

to protect themselves from them?

BAUER: Watch the National Weather Service warnings,

and if there's any wording about landslides,

then to not be within one of those

debris flow pathways or where the landslides might start.

There are online landslide maps available.

The North Carolina Geological Survey has put some out

so that people can go online

and see if they're in one of these areas.

And if they are,

they can then go stay somewhere safe.

NARRATOR: In Valencia, the flatter terrain,

and more urban environment,

created a different danger.

Here, cars became death traps.

Safety advice says you should never drive through flood water,

but for some in Valencia, there was no way to escape it.

[rain pounding]

KAREN LOFTUS: We were on the motorway.

It was raining very hard.

I've never been in rain

quite like it.

And the traffic came to a standstill.

Then we started to see that

the water wasn't going anywhere,

and it started to rise up from the motorway.

After about five minutes,

the water started to come in to the bottom of the car.

[water rushing]

The water continued to rise

to the point that our car engine did cut out.

STEVEN LOFTUS: Well, literally, the car is now floating sideways.

[thunder rumbling]

NARRATOR: The force of water pressing around the car

makes it impossible for Karen and her husband

to open the doors from inside.

KAREN LOFTUS: Oh, god.

NARRATOR: Luckily, they had lowered the windows

before the engine cut out.

KAREN LOFTUS: Within ten minutes,

I was having to get out of my car window

into what was a muddy, freezing cold torrent of water.

[water surging]

There were cars starting to float,

and some people had been able to get out

and some people were still in their cars,

obviously very frightened and scared.

There was a huge articulated lorry,

and we just thought, "we'll just try."

And we banged on the door of this lorry,

and then this wonderful Moroccan lorry driver drove us out.

♪

NARRATOR: They were lucky.

[metallic clang]

Many others were not.

[indistinct radio chatter]

♪

The floods in Asheville, Valencia, and Texas

were some of the worst experienced

in the western world in recent years.

In North Carolina, the storm k*lled people.

In Valencia, died.

In Texas, more than .

Casualties like these

are very difficult to prevent,

because flash floods happen so quickly.

But could there have been more advanced notice,

and timelier warnings to evacuate?

In the United States,

much of the necessary infrastructure

is already in place.

Two days before Asheville flooded,

the National Weather Service computer models and forecasters

accurately predicted that the flood could be

as big as the Great Flood of .

♪

But as the rain started to fall,

they needed to forecast

where flooding would occur,

and when.

PALMER: During the height of the event,

we had eight people here overnight,

and then three of those eight

were issuing flash flood warnings.

NARRATOR: To help predict floods,

forecasters in the United States

use a tool developed at

the National Severe Storms Laboratory in Oklahoma.

The system, called FLASH,

calculates where heavy rain will most likely cause a flood.

Across the country,

radars detect rain,

and tell forecasters

how much is falling.

But to predict a flood,

they need to know where that water will go

when it hits the ground.

JONATHAN GOURLEY: What is the condition of the land surface

that the rainwater is falling on?

A little bit will be intercepted by the vegetation.

Some of it gets infiltrated in the soils.

But in many urban areas

that are developed,

we don't have those soils as much,

and they've been replaced by asphalt and concrete

and buildings, and in general,

they have much less capacity

to absorb some of that incoming rainfall.

♪

NARRATOR: The FLASH system contains a grid

with details of the different terrain

in every square kilometer of the country.

GOURLEY: To run a simulation,

we have over million grid points

across the United States.

At every grid cell, we know the characteristics

of the land surface in terms of the vegetation type,

the composition of the soil, as well as the topography.

NARRATOR: The system uses this information

to calculate where the water will flow

and pinpoints areas at risk of flooding.

The total time FLASH takes,

from detecting rain as it falls

to predicting a flood,

is just minutes.

GOURLEY: The worst case scenario

would be about or minutes.

Here on this left screen is FLASH.

So, this is during the height of Helene.

FLASH is really helpful for us to determine

which areas are more likely to need

a flash flood warning first.

Especially at the beginning of an event.

Yellow is when

we're starting to think about

maybe the base flash flood warning.

The red to the purple is when we're thinking about

looking at that catastrophic or flash flood emergency.

NARRATOR: For Helene,

the National Weather Service's rainfall and flood forecasts

were pretty accurate.

But predicting a flood is only half the challenge.

The next step is to make sure people in danger know about it.

Here, Helene revealed

that the current system has a critical weakness.

The main method authorities use to inform people

is to send a wireless emergency alert to their cell phones.

The system works by using

the country's network of cell towers.

When there's a threat of an emergency,

such as a flash flood... [thunder booming]

...response officials mark the danger zone on a map.

[beeping]

They then send an alert message

to the nearby cell towers.

GPS coordinates of the danger zone

are encoded in the message,

so modern cell phones in or entering the zone

can trigger the alert,

which contains a warning message

advising people what to do.

PALMER:So, when we want to go to issue a flash flood warning,

we use this system.

So, I can just start drawing a polygon.

And if I want to send out

a Wireless Emergency Alert,

it has to be considerable or catastrophic.

Once I'm happy with everything I've typed in here,

I come down here to "issue all."

[click]

NARRATOR: When Helene unleashed its rain,

the team at this National Weather Service office

issued more than wireless emergency alerts

for flash flooding

in just two days.

But not all the messages got through.

The problem was the wind.

Hurricane Helene's winds were incredibly strong.

PALMER: As these winds were moving north,

it was a cascading power failure.

Trees were going down everywhere.

[crashing]

Power lines were being snapped.

So as the power grid was falling,

communications were going down,

just because power to the cell phone towers was failing.

Once you don't have the communications,

you can no longer get the wireless emergency alerts.

NARRATOR: In North Carolina,

the early forecast of major flooding,

and the wireless emergency alerts that did get through,

are thought to have saved many lives.

[click]

In Texas, the National Weather Service

also forecast the flooding.

The day before the floods,

it initiated a flood watch.

SHEPHERD: We know that from a meteorological perspective,

there were ample weather warnings

in the days and hours leading up to the event.

There are questions about how that information was

channeled into warnings

and risk communication for the public.

NARRATOR: Flash floods happen so fast

there is little time to take action.

Texas Hill Country was no exception.

At : A.M.,

the National Weather Service sent out a warning alert

to cell phones in the area of Camp Mystic,

a Christian girls' summer camp.

About minutes later,

the flood hit.

At Camp Mystic, at least girls and members of staff died.

In total, the Texas Hill Country floods

k*lled more than people.

SHEPHERD: We know that there were

not the type of warning systems

that we often would expect

in this type of complex terrain.

So, I think conversations going forward

will be centered around

how adequate were

cell phone notifications.

Is there coverage?

Are weather radios needed?

Is some type of siren or warning system needed?

These are all questions that certainly should be asked.

NARRATOR: And not only about Texas.

[crashing]

In Valencia, there were problems with both

forecasting and warning people.

CLOKE: We know that when we have

a good flood forecasting and warning system

and that people know what to do

when they receive those warnings,

that lives are saved.

So something went wrong in this flood.

We know that the flood forecasting and warning system

didn't work as it should have done.

NARRATOR: In Valencia,

weather forecasters saw the storm coming

well ahead of time,

and on the morning of the flood,

issued a red alert.

But their forecasts

underestimated the amount of rain.

They predicted that more than seven inches of rain

would fall in hours.

The highest actual amount

was inches--

over four times as much.

GOURLEY: One of the grand challenges

is predicting intense rainfall

that occurs over these really small spatial scales.

We may have like a broad area

where we're anticipating

some heavy rain,

but what does that mean?

Which city is going to be impacted?

And when I say heavy rain,

is it going to be a catastrophic rainfall event

that's going to annihilate the city,

or is it just going to be a spring thunderstorm.

It's very difficult to distinguish those two.

[lightning crashing]

NARRATOR: When the storm turned out to be

one of the biggest to ever hit Spain,

the emergency services were overwhelmed.

[person exclaiming, objects crashing]

[helicopter blades churning]

Unlike the United States,

Valencia didn't have a system like FLASH

to automatically predict where rain would cause floods.

Instead, it relied on more traditional methods.

Around the Poyo ravine,

rain gauges in the hills

sent back readings of rainfall every five minutes.

♪

On the ravine itself,

a sensor situated ten miles upstream of Paiporta

measured the flow of water.

When the rain increased in the afternoon,

the flow in the Poyo started rising rapidly.

At : P.M.,

it reached , gallons per second,

almost as much as the average flow of water

over Niagara Falls.

Then, the water swept away the sensor.

♪

Despite all the gauges and sensors,

very little of this information

appears to have reached the emergency committee meeting

responsible for sending out

the wireless emergency alert.

[click]

[inaudible shouting]

At : P.M.,

two hours after the Poyo River first broke its banks,

the cell phones of people across the province

made an alarm sound

and displayed a warning message.

[alarm tone]

KLARENBERG: The first warning I got was

after the streets had flooded.

My mobile started

kind of aggressively buzzing.

Yeah, so, after... after the fact.

KAREN LOFTUS: Had we received the alert,

which we did receive, four hours after the event,

of course we wouldn't have traveled.

It would've been a folly to travel.

NARRATOR: Many of the victims had died

before the alert was finally sent out.

♪

In Spain, an investigation is under way

to find out what went wrong.

But timely warnings alone

aren't necessarily enough.

In North Carolina and Texas,

warning systems were not always able

to get the messages through to the people at risk.

♪

National Weather Service advice

is to not rely on just one technology.

If for whatever reason,

whether you don't have your phones,

or there's not adequate cell phone service,

we need redundancy,

we need other ways of communicating the threat.

NOAA weather radio

is connected directly to NOAA

and National Weather Service warnings,

and so it will be triggered

irrespective of whether there's cell phone coverage.

PALMER: While cell phone towers

and cell phone communications went down,

NOAA weather radio stayed up.

So, we always recommend that folks have

a NOAA weather radio.

[person exclaiming, water surging]

NARRATOR: The disastrous floods in

North Carolina, Valencia, and Texas

are a wake-up call to authorities around the world.

SHEPHERD: I'm often asked

if this is a harbinger of things to come.

My response would be,

it's already here.

The atmosphere has warmed,

and the systems are tapping into

elevated moisture supply,

and we're seeing extreme rainfall events.

That's not my opinion,

that's what scientific studies are showing.

NARRATOR: Across the globe,

governments are taking action,

not only to improve warning systems,

but also to protect their citizens.

[rain pounding]

In Japan,

the annual number of heavy rainstorms

has increased by % over the last years.

It's a serious problem for the capital city, Tokyo.

[lightning striking]

When heavy rain hits, parts of the city flood.

To channel water away from rivers

that were at risk of overflowing,

in the s, engineers began building

a massive underground flood relief system.

Workers excavated

nearly four miles of tunnels beneath the city.

♪

Giant subterranean silos

were designed to store some of the water,

while a vast cathedral-like reservoir,

feet high, would hold the rest.

Yet, this extraordinary underground project

is still not big enough to cope with the increased rainfall

expected from global warming.

Work is now underway to double its capacity.

♪

The increased risk of flooding

in many places

is forcing planners and engineers

to rethink their designs.

CLOKE: Often, new engineering structures that go in

or the new plans that are in place

are all based on the last disaster that's happened.

But what we really need to do

is imagine what other types of flood might happen as well.

So that act of imagination, the act of thinking of

through those scenarios of the future,

is really important.

NARRATOR: In Asheville,

communities are attempting to rebuild.

It looks like they're trying to reconstruct it.

We all had to leave.

There were tons and tons of mud inside the building.

The first floor, completely wiped out.

I was able to find another place to live.

Some people left

and just didn't come back.

We actually still have

the window that we swam out of,

it's just not attached to the house anymore,

but this is the amount of space we had to swim out of.

♪

It's been a struggle in a lot of ways,

but we've had a lot of like

really skilled workers working with us,

and a lot of great volunteers.

All over the world people came to help people here.

The danger of the flood happening again

is something we have to take seriously.

We've applied for the elevation program.

So, eventually, our house is gonna be basically on stilts.

♪

NARRATOR: The flood has brought this Swannanoa community together.

BURGIN: We know them all so much better now.

We just want to stay in the area

and be around each other.

That's why everyone wants to rebuild.

That's why everyone wants to stay.

[water rushing]

NARRATOR: Floods will always happen.

But we have the technologies to make them less deadly.

CLOKE: We're in the position now where

we have good weather forecasts,

and we have good flood forecasting systems.

So we should be able to provide warnings to people

to make sure that they have the information they need

before floods hit.

SHEPHERD: We know that we'll continue to have extreme rainfall events

that will lead to flooding.

So, as we move forward,

we have to think carefully

about what type of warning and dissemination systems

are needed-- that's a clear need

in terms of risk communication

in Texas and in places around the world.

♪

NARRATOR: The science is clear:

with intense rainfall increasing,

more frequent floods are already here.