Hurricanes are intensifying more quickly. Is it time to change how we categorize them?

Transcript

ADRIAN FLORIDO, HOST:

Extreme weather is becoming more frequent, in part because of human-driven climate change - record-breaking heat, as we've seen in much of the U.S. this week, more frequent floods, like parts of the Midwest are dealing with, and stronger, more rapidly intensifying hurricanes. This new hurricane reality has some researchers wondering whether the classification we use to warn about the danger of the most powerful storms, Category 5s, is falling short. Is it time to add a Category 6? Alana Casanova-Burgess just reported on this for the podcast "99% Invisible." She joins us now. Welcome.

ALANA CASANOVA-BURGESS, BYLINE: Hi.

FLORIDO: You visited a facility in Miami called the Wall of Wind. What is the Wall of Wind?

CASANOVA-BURGESS: Yeah, it's actually a lab at Florida International University. It's a huge airplane hangar. They've got 12 large, yellow fans. They're each taller than I am. They're about 6 feet in diameter. And what scientists there have figured out how to do is to use those 12 fans to simulate hurricane-strength winds.

FLORIDO: And what is the Wall of Wind for?

CASANOVA-BURGESS: The Wall of Wind tests different building structures, different construction methods and materials against really, really strong winds. So they blast these test structures with the winds to see how can they get these buildings to not blow apart, right? Is there something they can modify with the shape of the roof? Are there different screws to use, different ways to attach a door so it won't blow open, all those things to figure out, how can buildings be made more hurricane proof? And right now they can get to 157 miles per hour. They can go up to a Category 5, which is technically 157 miles per hour and above, but they're hoping to actually go a little higher than that.

FLORIDO: Alana, your episode is about the Saffir-Simpson scale that meteorologists use to classify hurricanes. We've all heard it - Category 1, Category 2, Category 5. This is a former government official you spoke with.

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HUGH WILLOUGHBY: What the categories serve is, it says, the wind is going to blow really hard, and you want to do something about it.

FLORIDO: And what you dive into is the debate that's started to emerge about whether this scale is still effectively serving that purpose. Like, what is the actual purpose of this scale?

CASANOVA-BURGESS: Its purpose is to tell us what we can expect from a hurricane in terms of damage. In particular, it tells us about wind speed. So the different categories have different intervals of wind speed. But when you read the descriptions of each category, it's really an engineering scale. It tells us what we can expect from roof damage, whether there might be wall collapses, what could happen to mobile homes, our infrastructure, tree damage, things like that. So it's really about the physical impact of hurricane wind speeds on our built environment.

FLORIDO: So then why do some scientists think it might be time to change the scale, to update it?

CASANOVA-BURGESS: Well, the scale dates back to the '70s, and our built environment has changed a lot in the last 50 years, so that's one thing. We also know that different communities are vulnerable in different ways. So a Category 2 storm that hits a really vulnerable community that has very sensitive infrastructure is going to suffer a lot more damage. Another is that Category 5 is open-ended, so it goes on forever. And there's some debate among scientists that because hurricanes are getting more intense and intensify more quickly, there's an argument that maybe we need a Category 6 to capture storms like, for example, Hurricane Dorian, which hit the Bahamas in a really intense way that no one really expected. So...

FLORIDO: With wind speeds of over 180 miles an hour.

CASANOVA-BURGESS: Exactly. And so that is different from a storm that is 157 miles per hour, say. And there might be a difference in how those wind speeds hit buildings, hit our infrastructure, right? So it might - there might be a difference between a Category 5 and a Category 6.

FLORIDO: I guess on the surface that would make sense, right? I mean, if storms are getting stronger, shouldn't we have a way to communicate sort of the increased danger to the public? But why do some scientists disagree with, you know, the proposal to possibly add another category to the scale, a Category 6?

CASANOVA-BURGESS: Well, for example, what would someone do differently? One thing I heard from the National Hurricane Center, from Robbie Berg, who handles the coordination for warnings for the NHC, is that what would people really do differently in a Category 6? A Category 5 is already catastrophic. So is a Category 6 extra, extra catastrophic?

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ROBBIE BERG: It's still hard to understand, you know, what are we trying to achieve with calling something Category 6? Is it meant to get people to do something different than they should be doing with a 4 and 5? And then I think the next question is, where does it stop? Some of the social science has actually shown that when you have too many categories in a scale or too many, say, colors on a map, it actually becomes harder and harder for people to interpret that.

CASANOVA-BURGESS: There are some people who say, well, it could just be a way to communicate to the public about the increased dangers of climate change. For example, in Australia, the heat scale has two additional categories for the extreme heat that we're seeing as a result of global warming. So a Category 6 could be something like that. But would it then communicate really what the public should do differently, that they should evacuate extra hard for a 6 as compared to a 4? Those are the sort of questions that they're asking.

FLORIDO: The Saffir-Simpson scale measures wind, as you said, but any of us who live or have lived in a hurricane-prone region know that often, the wind isn't even the most destructive part of a hurricane, that in terms of danger to human life, the water usually kills more people. How is that fact complicating this debate and scientists' view of the path forward?

CASANOVA-BURGESS: This is really the biggest thing. I think Category 6 gets a lot of discussion. It gets people really heated up. But the fact is that the Saffir-Simpson scale doesn't have anything to say about water. It doesn't say anything about flooding or rain risk or the risk from storm surge. And that's because all those things are kind of complicated. It's hard to calculate storm surge. It's very dependent on the geological features around an area, so it's not exactly the same as wind speed. That's something that everyone I spoke to could agree on - that there's got to be a way to communicate to the public what the danger is from water because as you said, it does account for the majority of deaths in these natural disasters.

FLORIDO: Alana, any sort of big or surprising lessons you learned reporting this episode?

CASANOVA-BURGESS: Just thinking about how we are going to communicate the bigger risks in a warming world, right? What are the scales that we use to warn each other about threats? I mean, the Saffir-Simpson scale took a long time to come into being. It's been hard to get a grip on hurricanes for, like, pretty much all of human history, and now they're changing. And our built environment is changing, and just thinking about that enormous challenge of preparing ourselves and talking to each other about risk in a warming world is just - it's going to be really hard.

FLORIDO: I've been speaking with reporter Alana Casanova-Burgess. Her episode for the podcast "99% Invisible" called "Category 6" is out now. Alana, thanks so much.

CASANOVA-BURGESS: Thank you. Transcript provided by NPR, Copyright NPR.