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Why the Nepal flash flood was almost impossible to predict · INSIGHT TODAY

• 0:00
  Speaker 1: If you ever needed convincing that minutes matter, this was it.
• 0:04
  Speaker 2: Quick thinking and courage saved the lives of over 1,600
• 0:07
  Speaker 2: schoolchildren as devastating flash floods hit Nepal on Wednesday.
• 0:11
  Speaker 1: A wall of earth, ice, and water comes crashing down
• 0:15
  Speaker 1: a mountain thousands of meters high. All that debris and
• 0:19
  Speaker 1: flash flooding barreling through the valleys of Nepal and this
• 0:22
  Speaker 1: school is about to be wiped off the map.
• 0:25
  Speaker 3: An entire river valley along the Nepal border wiped out
• 0:28
  Speaker 3: in seconds.
• 0:29
  Speaker 1: Because absolutely everything is getting destroyed. A monster wave crashing
• 0:34
  Speaker 1: down from the mountains, sweeping away everything in its path.
• 0:38
  Speaker 1: Entire towns washed away. But this school, which was also destroyed,
• 0:48
  Speaker 1: best as I can tell, not one student died.
• 0:52
  Speaker 4: I was inside my classroom.
• 0:54
  Speaker 1: One of my colleagues, one accountant came there and he
• 0:57
  Speaker 1: said that the flood is coming, the flood is coming,
• 0:59
  Speaker 1: all areas washed away. The principal you just heard figures
• 1:03
  Speaker 1: he had about 13, 14 minutes to get nearly a
• 1:06
  Speaker 1: thousand students out of school and to higher ground. In
• 1:10
  Speaker 1: the chaos of the evacuation, he even had the foresight
• 1:12
  Speaker 1: to reroute buses full of younger children that were on
• 1:16
  Speaker 1: their way to school, telling them, don't come, get somewhere safe.
• 1:20
  Speaker 1: This is one incredible outcome in a disaster full of
• 1:24
  Speaker 1: terrible ones. But it also raises a question. If someone
• 1:29
  Speaker 1: knew this flood was coming Why didn't everyone get that call?
• 1:39
  Speaker 1: Even if you knew nothing about Nepal, I could situate
• 1:41
  Speaker 1: this for you by saying this disaster happened about 100
• 1:45
  Speaker 1: or so kilometers west of Mount Everest in the Himalayas.
• 1:48
  Speaker 1: And when we think about floods in this part of
• 1:51
  Speaker 1: the world, especially during monsoon season, which it is now,
• 1:55
  Speaker 1: we're often thinking torrential downpours of rain. That's not what
• 1:59
  Speaker 1: this was.
• 2:00
  Speaker 4: What we really saw was that the lower part of
• 2:03
  Speaker 4: a tongue of a glacier completely sheared off across a
• 2:06
  Speaker 4: width of 1,300 meters. And it's really like someone took
• 2:09
  Speaker 4: a knife and basically cut the lower part of a
• 2:11
  Speaker 4: glacier and dropped it off the mountain cliff.
• 2:14
  Speaker 1: Yes, this wasn't initially water, but rather the earth and
• 2:18
  Speaker 1: its ice that came crashing down. It's here on the
• 2:22
  Speaker 1: northern face of the Langtang Range where this massive glacier
• 2:27
  Speaker 1: is believed to have collapsed. detaching from the mountainside more
• 2:30
  Speaker 1: than 5,000 meters above sea level, sending an enormous amount
• 2:34
  Speaker 1: of ice, rock, force, and energy screaming thousands of kilometers
• 2:40
  Speaker 1: down a steep slope. The avalanche would ultimately tear through
• 2:44
  Speaker 1: the twists and turns of the valley, slamming into a river,
• 2:48
  Speaker 1: sending an immense amount of water, mud, and debris into
• 2:51
  Speaker 1: nearby Rasu-Wagadi, a gateway between Nepal and China, destroying it
• 2:57
  Speaker 1: in seconds. The flash flood continued south, gathering more water,
• 3:02
  Speaker 1: scarring the riverbanks, swallowing entire settlements along the way. Timur
• 3:08
  Speaker 1: and surrounding towns basically disappeared. Further south, Sebrubesi, it was
• 3:14
  Speaker 1: considered a hub of the region. Thousands lived on either
• 3:17
  Speaker 1: side of the river and tourists came here too. If
• 3:20
  Speaker 1: you wanted to trek through Nepal's mountainside, you might start here.
• 3:24
  Speaker 1: But the whole area absolutely ravaged. Dams, buildings, highways, bridges
• 3:31
  Speaker 1: washed away. And the destruction this flood carved through the
• 3:35
  Speaker 1: country would eventually reach more than 100 kilometers away from
• 3:39
  Speaker 1: where it started. It all happened very quickly, too quickly.
• 3:44
  Speaker 1: There are warning systems in place, but they're not really
• 3:48
  Speaker 1: designed to track this kind of disaster.
• 3:51
  Speaker 3: So one of the only monitoring systems that we have
• 3:54
  Speaker 3: in place are river gauges that can track when there's
• 3:58
  Speaker 3: a sudden increase in the water level. That can trigger
• 4:02
  Speaker 3: a siren downstream that can hopefully get to the communities
• 4:07
  Speaker 3: that need it in time for them to evacuate.
• 4:10
  Speaker 1: Water is a major threat in these mountain ranges, but
• 4:14
  Speaker 1: flooding is usually driven by rain or by melt, things
• 4:19
  Speaker 1: you can track in real time. So river and lake levels,
• 4:22
  Speaker 1: for example, can rise during monsoon season, or you can
• 4:25
  Speaker 1: have glacial meltwater pool and then burst its banks. Point is,
• 4:31
  Speaker 1: it tends to happen gradually in a way that these
• 4:34
  Speaker 1: river gauges can actually measure over time and then relay
• 4:37
  Speaker 1: that data downstream to where it's useful. Except in this case,
• 4:42
  Speaker 1: it would have been like measuring the direction of a
• 4:45
  Speaker 1: hurricane by holding out a finger. The speed of the
• 4:49
  Speaker 1: flood was so overwhelming. The sudden flow so catastrophic. In
• 4:54
  Speaker 1: some cases, it destroyed the monitoring systems before they could
• 4:58
  Speaker 1: even send their alerts.
• 5:00
  Speaker 3: So we went from, you know, real time data to
• 5:04
  Speaker 3: all of a sudden there.
• 5:05
  Speaker 5: Was no information.
• 5:07
  Speaker 1: So how do you warn people about a disaster that
• 5:10
  Speaker 1: moves faster than the warning system itself? The thing is,
• 5:19
  Speaker 1: there's a lot we understand about how these disasters happen.
• 5:23
  Speaker 5: This is absolutely an event of a type that occurs
• 5:27
  Speaker 5: in the Himalayas. It has occurred many times in recent
• 5:30
  Speaker 5: recorded history.
• 5:31
  Speaker 1: And even in those cases where people are in danger,
• 5:35
  Speaker 1: There are success stories, like in Switzerland. Now, don't get
• 5:39
  Speaker 1: me wrong, what happened in the small Swiss mountain town
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  Speaker 1: of Blatten last year was tragic. An entire community was
• 5:46
  Speaker 1: buried under an avalanche of ice and rock. Authorities say
• 5:51
  Speaker 1: 90% of the village of Blatten has been covered by
• 5:53
  Speaker 1: thousands of tons of ice, mud, and rock. But nearly
• 5:57
  Speaker 1: every single person survived because the town had been evacuated
• 6:02
  Speaker 1: more than a week earlier. Hundreds of people fleeing the
• 6:06
  Speaker 1: area well in advance because of what locals and scientists
• 6:11
  Speaker 1: had been noticing for years.
• 6:13
  Speaker 5: In the European Alps, the mountainside collapse in Blaten, Switzerland,
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  Speaker 5: a year or so ago, that was known to be
• 6:22
  Speaker 5: an issue well before it happened.
• 6:24
  Speaker 1: These are photos from a Swiss natural hazard monitoring company
• 6:28
  Speaker 1: showing Radar and camera setups pointed directly at the mountain,
• 6:33
  Speaker 1: which they had believed at the time might give way
• 6:36
  Speaker 1: at any moment. This type of precise measuring equipment can
• 6:39
  Speaker 1: reveal even the tiniest details about a mountain. Its cracks,
• 6:44
  Speaker 1: its movement, the slightest changes in position. And what that
• 6:49
  Speaker 1: equipment detected was this. What you're seeing here is a
• 6:53
  Speaker 1: 26-hour time lapse from the same Swiss company, Geoprevent, just
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  Speaker 1: before the glacier collapse. Maybe seemingly slow, but alarmingly fast
• 7:04
  Speaker 1: for a mountain. The Earth was moving 10 meters a day.
• 7:09
  Speaker 1: With this kind of information, you can't predict the exact
• 7:13
  Speaker 1: timing of the collapse itself. But this kind of observation
• 7:17
  Speaker 1: is what allowed scientists to recognize The increasing chance that
• 7:21
  Speaker 1: something bad might happen at some point, the danger was
• 7:25
  Speaker 1: progressive and predictable.
• 7:27
  Speaker 2: It's easier to access some of those cliff sides in Switzerland,
• 7:30
  Speaker 2: get sensors and monitoring equipment in those locations so that
• 7:34
  Speaker 2: we can get real-time data. Here in Nepal, the extreme
• 7:38
  Speaker 2: elevations we're looking at, there's no trail to the top,
• 7:42
  Speaker 2: there's not a cable car there.
• 7:43
  Speaker 3: The capacity and the resources necessary are gonna be very
• 7:47
  Speaker 3: difficult to replicate in places like the Himalayas.
• 7:51
  Speaker 1: It's one thing when you've been noticing changes over a
• 7:53
  Speaker 1: long period and you decide to point a whole bunch
• 7:56
  Speaker 1: of measuring devices at a very specific spot. But the
• 7:58
  Speaker 1: problem with the Himalayas is scale.
• 8:01
  Speaker 5: The physical scale of the range, the difficulty in working
• 8:04
  Speaker 5: with it, the fact that it's often covered in clouds
• 8:06
  Speaker 5: as it is due to the monsoon season now, it
• 8:09
  Speaker 5: prevents tremendous challenge for prediction and monitoring.
• 8:14
  Speaker 1: This part of the world isn't just a mountain range.
• 8:18
  Speaker 1: It is an entire wall of mountains stretching thousands of kilometers,
• 8:24
  Speaker 1: containing some of the highest peaks and deepest valleys on Earth.
• 8:28
  Speaker 1: Glaciers and the lakes they melt into are a key
• 8:31
  Speaker 1: concern because they can overflow. But there are thousands of
• 8:35
  Speaker 1: them across Asia, and scientists do their best to track
• 8:38
  Speaker 1: every single one, with reports like this one from 2020
• 8:41
  Speaker 1: creating a meticulous inventory of the most dangerous sites, like
• 8:46
  Speaker 1: One giant catalogue of risk. There's promise there, maybe, you'd think.
• 8:52
  Speaker 1: And looking in hindsight at what happened in Nepal, they
• 8:55
  Speaker 1: are indeed finding clues that suggest maybe these types of
• 9:00
  Speaker 1: events are predictable. A new report published after the collapse
• 9:04
  Speaker 1: refers to how movement of the ice surface sped up
• 9:07
  Speaker 1: just prior. How meltwater had turned visibly brown, suggesting mountain
• 9:13
  Speaker 1: sediment was shifting. Also, noticing a crack propagating in the
• 9:17
  Speaker 1: days leading up to the disaster. Even learning to better
• 9:20
  Speaker 1: track events as they occur. Noticing that the mass movement
• 9:24
  Speaker 1: caused a seismic signal at a magnitude larger than four.
• 9:29
  Speaker 1: So maybe there's promise in deploying more seismic sensors. And
• 9:33
  Speaker 1: imagine tying all that knowledge together, pushing it to the
• 9:37
  Speaker 1: limit using A.I., Combining susceptibility maps with real-time data to
• 9:43
  Speaker 1: inch closer and closer to predicting the unpredictable. But then
• 9:47
  Speaker 1: you remember, once again, the problem of scale. I think
• 9:51
  Speaker 1: one Washington-based think tank put it best. The Himalayan region
• 9:56
  Speaker 1: offers more slopes capable of failing at this magnitude. across
• 10:00
  Speaker 1: greater vertical relief than anywhere else on Earth. Then it
• 10:05
  Speaker 1: goes on to this point of how hard it can
• 10:08
  Speaker 1: be to gauge risk even when you think you've found it.
• 10:11
  Speaker 1: Of roughly a dozen extreme flow events in the region
• 10:14
  Speaker 1: in the past 10 years, only one originated in a
• 10:18
  Speaker 1: place already known to be a risk. Every other one
• 10:22
  Speaker 1: of these events also came from somewhere no one was watching.
• 10:27
  Speaker 6: It's very challenging to predict exactly where and when these
• 10:31
  Speaker 6: rock collapses are going to occur.
• 10:33
  Speaker 5: It would be terrific if you could put.
• 10:36
  Speaker 6: Sensors in in all the locations where events like this
• 10:39
  Speaker 6: potentially were going to happen. But it's just not practical
• 10:42
  Speaker 6: to monitor so many different locations all at once.
• 10:47
  Speaker 5: Remote sensing technologies improve, as computing improves, we'll be more
• 10:53
  Speaker 5: and more able to watch the landscape and detect small
• 10:57
  Speaker 5: amounts of change, but that's still a work in progress.
• 11:01
  Speaker 1: And that's really the key to all of this. Right now,
• 11:04
  Speaker 1: there is no crystal ball, just small incremental ways scientists
• 11:10
  Speaker 1: are learning how to buy precious seconds, maybe even minutes.
• 11:14
  Speaker 1: But trying to prevent or even predict changes the inevitable,
• 11:18
  Speaker 1: National Geographic referred to these glaciers as cryogenic time bombs,
• 11:23
  Speaker 1: a reference to our changing climate and how frozen water
• 11:26
  Speaker 1: that makes up this kind of glue that binds the
• 11:29
  Speaker 1: earth together, the cryosphere, it's melting. Is that to blame
• 11:35
  Speaker 1: in Nepal? We may never know directly, but it is
• 11:39
  Speaker 1: why scientists are so certain something like this will happen again.
• 11:43
  Speaker 1: It's just a question of when and where.
• 11:49
  Speaker 2: Thank you.