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After landslides killed three locals in Sitka, the Alaska city responded with science

AILSA CHANG, HOST:

Another heavy storm system is bearing down on the West Coast, threatening more flooding, landslides and other hazards. It's known as an atmospheric river, just like the damaging storms that soaked California earlier this year. It's the kind of extreme weather event that we're likely to see more of in a changing climate.

And for lessons in how to adapt to this new reality, we look to Sitka, Alaska, which had its own encounter with the weather phenomenon. In 2015, an intense atmospheric river triggered a series of landslides. Sitka chose to respond with science. Emily Kwong and Aaron Scott, the hosts of NPR's daily science podcast Short Wave, have this story.

EMILY KWONG, BYLINE: Sitka's on an island on the edge of the Pacific Ocean, in the Tongass National Forest. It's beautiful there, and it rains a lot - over 100 inches a year.

(SOUNDBITE OF RAINFALL)

LISA BUSCH: We have beautiful rivers with salmon, and the salmon need rain. Our ecosystems need a lot of rain.

KWONG: This is Lisa Busch, executive director of the Sitka Sound Science Center. And Lisa never feared the rain before, but the morning of August 18, 2015, was different.

BUSCH: I remember my pants getting wet, like, all the way up to my knees just walking from my car to the airport. So I remember thinking, this is a lot of rain - a lot of rain.

KWONG: Rivers in town began to rise, and the land started to slide. Forty landslides were documented on Baranof and Chichagof islands that day. A slope above a subdivision of new homes under construction gave way.

(SOUNDBITE OF MUSIC)

KWONG: This landslide - the Kramer Avenue landslide - demolished a building and took the lives of three Sitkans - brothers Elmer and Ulises Diaz and Sitka's building inspector, William Storz. For days, Sitkans were shoveling debris, cooking casseroles, keeping vigil with the families of those lost and coordinating shelters for those evacuated.

UNIDENTIFIED PERSON #1: (Reading) I can stay with a friend, so my whole house is open.

UNIDENTIFIED PERSON #2: (Reading) Charteris (ph) has room.

KWONG: These are locals reading Facebook posts written at the time.

UNIDENTIFIED PERSON #3: (Reading) My home is very small, but I can offer food, blankets.

UNIDENTIFIED PERSON #4: (Reading in Spanish).

KWONG: The thing for Lisa at the Sitka Sound Science Center to do was to get answers. Why did this happen? Why did this rain tip the scale the way it did? And how do you stop a tragedy like this from ever happening again?

AARON SCOTT, BYLINE: Yeah. I mean, those are huge questions. Who do you call for something like that?

KWONG: You call scientists.

SCOTT: (Laughter) Of course you do.

KWONG: I mean, Lisa dialed everyone - NASA, the National Forest Service, the National Park Service, the U.S. Geological Survey.

BUSCH: They responded so quickly - yes, how can we help you with our expertise?

(SOUNDBITE OF BLUE DOT SESSIONS' "COPLEY BEAT")

KWONG: And all of their expertise, after years of work, led to an early warning system for landslides in Sitka, a system that's constantly updating based on the weather. And anyone can access the dashboard by typing sitkalandslide.org.

SCOTT: OK. So I'm looking at a clean page. There's a green checkmark that says the current risk of landslide is low, and the 24-hour forecast is also low. So this is reassuring.

KWONG: Mmm hmm. It kind of works like a traffic light system.

SCOTT: Right, right, right.

KWONG: And you saw for yourself it's really simple to look at. But developing a system that's both science-backed and user-friendly took seven years, a $2.1 million grant from the National Science Foundation and the involvement of an entire town.

SCOTT: So if you're surrounded by these hillsides, how do you know which ones are at risk of sliding?

KWONG: This is the where piece of the puzzle. Where do landslides happen? I'm going to let Jacyn Schmidt, a local geologist, show us that.

JACYN SCHMIDT: Hey, Emily. I'm here in the field. And I'm at the head scarp, so it's the place where it all started.

KWONG: A debris flow - that's the type of landslide we're talking about here.

SCOTT: OK.

KWONG: It happens when you get a lot of water in the system. Water that travels down through gravity and transforms layers of earth into a slurry of mud, water and other debris, taking on the consistency of wet cement. It can move up to 25 mph, giving you very little time to get out of the way.

SCOTT: And so this is what happened on Kramer Avenue in 2015?

KWONG: It is.

SCOTT: OK.

(SOUNDBITE OF CHAD CROUCH SONG, "SAVER")

KWONG: And geology tells us that new landslides are likely to form in the footprint of these old landslides, which is telling. So when Sitka's GeoTask Force started discussing that, the Forest Service, Lisa says, was like, hold on.

BUSCH: We have a landslide inventory that we've been keeping track of for the last 50 years in the area. Would that be helpful? And we were all like, what (laughter)?

KWONG: Historical data? Yes.

BUSCH: Hello? We didn't even know that they were doing that.

SCOTT: I love it when discovering a database is like discovering hidden treasure.

KWONG: Yes. And that trove of data wound up in the hands of Annette Patton, a postdoc at the University of Oregon and now lead geologist on this project. So with a sense of how slopes have failed before, Annette, along with Josh Roering at the University of Oregon, wanted to know what amount of rain tips the balance.

SCOTT: So, like, do certain amounts of rainfall predictably lead to landslide risk?

KWONG: Something like that, yeah.

ANNETTE PATTON: Like, if it rains really hard for an hour, is that what triggers a landslide? We didn't know for sure exactly what timescale of heavy rainfall would trigger a landslide, so that's where we wanted to start.

KWONG: So Annette combined this landslide inventory that the Forest Service happened to have with Sitka's rain record - 20 years of data gathered at the airport. She started to see a pattern. Five of the most catastrophic landslides in the last decade - ones that blocked roads, destroyed human life and property - they all saw a certain amount of rain in a three-hour interval.

SCOTT: Ooh, so how much? How much rain?

KWONG: It's not an absolute because the model is more designed to calculate probability. So a high-risk probability warning is triggered around 1.3 inches of rain in a three-hour interval. And along the way to creating this early warning system, the Science Center consulted the community as much as possible.

(SOUNDBITE OF MUSIC)

KWONG: Sitka Tribe of Alaska contributed traditional knowledge about landslides and human movement. That's on the dashboard. And to make sure the warning system actually reaches everyone in town, the Science Center decided to map the social networks. Robert Lempert led this part. He's a senior scientist at the Rand Corporation and hosted all of these co-design workshops.

ROBERT LEMPERT: We ran a game - an exercise - where we asked everybody in the room - and there's about 20 people or so - to fill out a little form and say whom in the room would they take shopping for clothes to get good advice on, you know, what to buy?

KWONG: And certain names kept coming up again and again - fifty people who should know about the landslide early warning system.

LEMPERT: And this idea that you've got individuals who have worked through the process who now, you know, trust this body of information and trust each other.

KWONG: This kind of collaboration, it's only becoming more important, right? I mean, these landslides, they're connected to climate change. Southeast Alaska is going to see more extreme rainfall.

SCOTT: Yeah. I mean, a lot of places are going to see more rainfall. Which raises the question, are other communities taking note of this project?

KWONG: Yes. Yes, communities who also worry about landslides and other things, which is why the science center hopes to bring this predictive modeling to six other rural and tribal communities in southeast Alaska.

SCOTT: Oh, great.

KWONG: The NSF-funded project, which is called Khutí- which is the Tlingit word for weather - hopes to create a regional system for warning people about flooding, avalanches and landslides. These natural hazards can't be stopped, at least not yet. But Lisa Busch says people can learn to live with them.

BUSCH: It's heartening to see a community adapt and move on. Yes, we have to live among landslides. We have to live in a changed world. And that's not easy, but it's heartening when people do it.

KWONG: Especially, Aaron, I think at the local level to keep people safe - I can't think of a better use for science.

CHANG: That was Emily Kwong and Aaron Scott from NPR's daily science podcast, Short Wave. Transcript provided by NPR, Copyright NPR.