Short Wave - Australia's Next Danger: Mudslides

Episode Date: February 24, 2020

With many of Australia's hillsides stripped bare by fire, scientists are rushing to predict where mudslides could be triggered by rainfall. NPR science reporter Rebecca Hersher and photographer Meredith Rizzo traveled to Australia to learn how they're doing it. More of their reporting (with photos) is here. Email the show at [e-mail]. See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Maddie Safai here with NPR science reporter Rebecca Hersher. Hey, Becky. Hey. So Australia, you just got back. Yep, still jet lagged. And so are the fires there still burning or are they out? They're mostly out. We have mostly moved beyond that. It's been raining a ton for the last few weeks.

But that means we've moved into a new danger zone. After it's been raining, there are mudslides. That started off good and then got bad. Yeah, that happens, actually, when I talk. Yeah. So, yeah, unfortunately, the types of fires that we're seeing in Australia recently, they make mudslides way more likely when it rains, which it's been doing. And that's because large, intense fires burn through hilly areas,

and then most of the trees are charred, the underbrush, like all those smaller plants, they're gone. Right. And the soil in those areas changes too. It kind of dries out. The top layer can basically become ash. Exactly. And so when it rains, the soil can't soak up the water as well. The water starts to run off and then mudslide.

Okay. And that basically happens without warning. I mean, for a long time, the answer was yes, no warning. But scientists are trying to turn that yes into a no. And we hung out with some of those scientists in Australia while we were there. It's pretty amazing what they've accomplished so far. So today in the show, the damage after the fire. How scientists in Australia are using satellites and helicopters to try and predict dangerous mudslides. Okay, Becky, you brought a friend with you today.

Yes, I did. The one and only Meredith Rizzo and PR photographer extraordinaire. Hey, Rizzo. Hey. I'm very excited to see you in this here studio. But what are you doing here? So like Becky said, I'm a photographer. I work with images.

And recently the two of us were reporting in Australia together where we met these scientists. A lot of what they're doing has to do with imaging, like what the landscape and the soil look like up close and from helicopters and even from space. So you're here for your visuality expertise? Most definitely, yes. Okay. I am employed to look at things. Yes. Okay.

So when I think soil scientists, the first things I think are not helicopters or space. I think of people with little shovels walking around, scooping up dirt, maybe looking at them under a microscope. Yeah. I mean, that's what we thought too going into it. But that is not how the soil science actually works. It's way more sexy. Okay, Meredith, I don't know what kind of show that you think this is, but please be appropriate while you're here. Okay.

All right. So, Dirt Nerds, using satellite images to study pictures of mud. I love this. I thought you would. I thought you would. But actually, some of what makes it sexy comes from what makes it challenging. This science is hard because you're dealing with huge areas. Like, you have to go up in space or up into helicopters to see the scale of these fires.

Like since last fall, almost 8 million hectares of forest have burned. Okay. Probably a hectare is in a unit that you're that familiar with. That's an area almost the size of South Carolina. Oh, yeah. Wow. Okay. Yeah.

So really, really big. And a lot of that has been on the southeastern coast, which is near some really big population centers, places you've heard of. Sydney, Canberra, the capital. And there are lots and lots and lots of small towns in the hills outside those cities. The fires burn through a lot of the forest that's right around those towns. So basically they have like a lot of land to cover. Exactly.

And a lot of people in potential danger from these mudslides that could happen. Every major fire that burned near where people live needs to be investigated to figure out where the mudslides are most likely to happen. And there aren't that many scientists that do this work in Australia. So the ones that do have the expertise have basically been working continuously for months because there's just so much land to be studied. So normally a 100,000 hectare fire would be a very, very large fire. but in the context of this year, it's actually probably going to be the smallest of the fires that we're deployed to.

So that's Charlie Showers. He's in like an incident command center. I can hear everyone in the background, like bustling around. He's a groundwater geologist. So he works for the Department of Environment, land, water, and planning for the Australian state of Victoria. It's basically like a state level EPA type entity.

And the fire he was working on when we visited him had burned through, as he said, about 100,000 hectares. So that's about 350 square miles. Wild. In this national park that has really steep mountains. So the fire had just gone out, like a day or two before we visited, and then it had rained a ton.

Actually, as we were driving in, it was like pouring rain. So mudslides might already be happening there, and he was trying to find them. There's probably not many hotspots at the moment, but... Yeah, so this is where the images really come in handy. Charlie has a lot of information available to him. about what's happening on all those acres of land. He has satellite images of the fires. He showed us these maps.

They update every day. So this is satellite hotspots here, so these little orange dots. He's showing areas of active fire. In addition to active fires, the satellites can look at burned areas too, so Charlie can see where the fire damage is most severe. Basically, where the tree cover is missing the most,

which is helpful because, the more intense the fire, the more unstable the soil. And the unstable soil is more likely to become a mudslide. Yeah, exactly. But the satellites aren't perfect. So there's a woman on his team named Estreya Malera Blanca, whose job it is to circle all the areas where there's not good satellite imagery. Like maybe there was a cloud in the way or even smoke.

Okay, so how do they get around that? Well, she can send someone in a helicopter to go look at the, those places and see how badly they're burned. This is more helicopters than I was expecting for this soil science episode. I wasn't expecting no helicopters, but this is more. These scientists are going up almost every day after

a fire is over and looking at trees, looking at the soil, taking lots of photos, and they're looking for evidence of mudslides. Because if there are small mudslides happening up in the woods, then that tells you that, yes, the soil is unstable here. And other areas that are

closer to people's houses or next to roads might also be unstable. Yeah, and this is where Charlie and Australia and their whole team are relying on the work of academic scientists, both in the U.S. and in Australia. Together, they've all made a lot of progress on two big questions. Ready? Yep. One, which hillsides are most at risk for these mudslides, which scientists refer to as debris flows? Okay. That's the technical term. And second, how much rain is necessary to trigger these debris flows? Right, because presumably, like, a light drizzle isn't going to unleash one. Exactly. A lot of rain in a short period of time is what's dangerous.

So they're looking at a lot of fire data, a lot of rain data, and looking for patterns about where these debris flows happen. The more data they have, the more the patterns emerge. Okay, so they've found these patterns. What do you do next? You build a computer model. What else? It's 2020. One that shows the risk of a debris flow happening in each individual place. So we visited one of the labs that's building one of these models. Gary Sheridan's lab at the University of Melbourne. This guy, Gary Sheridan, is really jazzed because they've been working on this model since 2003, and they've just rolled out a new version of it, which shows which areas are at the highest risk for debris flow.

And you can actually see the risk when you look at the maps they've made. So, for example, you know, say it rains like six inches in two hours in an area that burned very severely two months ago. and the slope of the hill is this, how likely is that debris flow will happen? If the risk is high, there will be a little red dot in that area. If it's medium, there might be an orange dot. Okay, so in general, how common are these debris flows? Like, are they happening all the time after fires, or does it take a really rare, powerful rainstorm to trigger them?

Yeah, Gary Sheridan actually put it really succinctly. Yeah, people who talk about freak mud flows and freak landsides after the fire. and there was always this idea that these things were extraordinary events. But as we found and you guys in the US have found too, the kind of rainfall that triggers them off, although it's intense and very short, it's actually quite a common rainfall event. And if the rain is that common,

then the debris flows themselves are also pretty common. Although not necessarily huge debris flows, it can be lots of little mudslides that are triggered. So how does all this come together to help protect people? Like, are the scientists who are out, looking at the areas that burn this year, able to use this information to warn people in, like, a specific area? Yes and no.

The model still isn't quite good enough for, like, local officials, like your local fire chief to just log on and make decisions based on what they see. Like, there are a bunch of red dots on the map. I'm going to close this road that runs up to this hill. It's not good enough to make that kind of decision. But the model that Sheridan's team built is helping with kind of broader decision-making. Like, if a debris flow is really likely to happen in a. given watershed, for example, the towns that rely on the streams in that watershed

might switch to pumping groundwater for drinking water because the rivers are likely to get pretty muddy, right, if you're seeing a lot of debris flows. Or if firefighters in an area that has burned are trying to get to places that are still on fire, they can use this model to decide which areas are safer than others. And that's important because at least one firefighter in Australia has died in a debris flow. So it's a big deal. Okay, Becky Herscher and Meredith Rizzo. I appreciate you both. Thanks. We've got a link in our episode notes where you can see some of the photos by Meredith from her trip with Becky to Australia.

This episode was produced by Brett Bachman, edited by Viet Le, and fact-checked by Emily Vaughn. I'm Maddie Safaya. We're back tomorrow with more shortwave from NPR.