[water rushing] [metal scraping] [somber music] - [Narrator] The river is receding.

What Hurricane Helene left in its wake has left residents stunned as to where to start with the cleanup.

Areas like the River Arts District in Asheville were nearly wiped away by the French Broad River.

- That's like 25, 27 feet or something like that.

- Something like that.

Yeah, our heads would definitely be underwater right now.

- [Narrator] Carl Schrek knew it would be bad, just not as bad as it turned out to be.

- Friday morning of the storm, as it was approaching, I was getting text messages from a friend at the National Hurricane Center saying, "You're about to see some really crazy stuff.

The eye wall is headed right for you."

And this was just as power was out, cell phone was already starting to die, so I couldn't watch the radar to see where this storm was approaching in the hours and minutes before it came.

So, it was really scary.

[wind gusting] - [Narrator] "While we've always had hurricanes," Schrek says things are different "because of climate change."

[motor rattling] He says "As the Gulf of Mexico gets warmer, it tends to serve up better conditions for systems to form."

[wind gusting] - Hurricanes are especially efficient at ringing that extra moisture out, so they're causing the heavy rainfall like we saw with Helene, was even heavier because of climate change.

Also, down at the coast, we know that sea level is rising.

So, anytime you have a storm pushing storm surge onto the land, it's starting from a higher [onlookers shouting] level, you're gonna get even more storm surge just from that additional sea-level rise that we've already observed.

So those two things we're really, really confident about.

[somber music continues] We think, probably, we're getting about the same number of storms as we used to, and we're not really gonna get more of them, but the ones we get are probably going to be stronger than they used to because the ocean is getting warmer, and the ocean, that's provides the fuel to make these hurricanes.

[wind gusts] [bright music] - [Narrator] Helene made landfall along the Florida coast September 26th as a Category Four hurricane who sustained winds of 140 miles-an-hour.

[winds gusting] It weakened to a tropical storm as it moved northward and inland, but brought more water [water rages] than anyone had ever seen in a weather event in the state history.

By the end, Helene had dropped an estimated 40 trillion gallons of water on the region.

- So anytime it rains, it's raining harder now than it would have 100 years ago.

- [Narrator] But climate change alone isn't what made Helene so devastating.

Call it bad luck, meteorologists call it a "predecessor event," a rain system that happened to hit the area just before Helene arrived.

It truly was the perfect storm and not the good kind.

- All that moisture from the hurricane coming up, running into a cold front that makes it rain, running into a mountain that makes it rain even more.

And then you have it raining on either side of the mountain and all that rain's going down into a valley, that valley is going to flood very quickly with all of that rain coming together.

- All these questions about weather and climate make understanding trends and global-event monitoring crucial.

[pensive music] - I don't even know where you begin to clean this up.

In these reports, we talk about extreme weather, we talk about where it's occurred, what's happening, how it compares to the historical record.

That's part of what we do.

We also track billion-dollar weather and climate disasters, of which this will likely be one of those disasters.

It has so much fire hazard- - [Narrator] Karen Gleason says, "Monitoring rainfall itself is a fundamental part of what they do.

And what they know best about hurricanes and climate is that they know hurricanes are getting wetter and they know that as the climate warms, there's more water vapor and more moisture in the air."

- I mean, we have such, you know, varying topography in Western North Carolina that 16 inches of rain in one place can be 6, 9, 12 feet of rain in another because of the way the water runs from a high location to a low location.

And that creates intense, very rapid flash-flood events.

So really having the one-two punch of this predecessor rain event followed by Helene really made this particular event as catastrophic as it was.

[pensive music] - [Interviewer] What was this?

- This is my roof from the building-block building over there, so.

- [Narrator] Greg Weiss has worked in high-end renovation and green buildings since 1982.

He says they're looking at other locations for his woodworking business in the area, but won't be returning here.

- That floated off with my solar panels and the pitched roof, as well as the U-Haul trailer that had all our high-end equipment in it and washed away, and when it went up to 29 feet.

- [Interviewer] What are you feeling right now after walking through this?

- Well, you know, it's like, what are we gonna do?

[somber music] - [Narrator] Gleason says "it's an art to take the complexities of science and data they collect and explain it in a way that people quickly understand."

- You know, we try to make it as relatable as possible because that's the point.

You know, we're trying to communicate science to people and tell them why this all matters.

[somber music continues] - [Narrator] Helene left a swath of destruction not seen in over 100 years, and officials say the cleanup costs may top "$50 billion by the time it's done."

But these costs in no way factor in the human element.

For Carl Schrek, the experience of seeing face-to-face what he has studied for decades suddenly come to his doorstep is something he won't forget.

- My children go to school with some kids that actually lost their lives in the hurricane.

So, actually knowing people that were so incredibly affected by it is really heartbreaking.

[somber music continues]