A recent study from Portland State University assessed the likelihood of environmental hazard risks, identifying many “multi-hazard hotspots” — areas that are at risk of overlapping climate hazards — along Interstate 205.
The study looked at four climate risks, including fire, urban heat, flooding and landslides. The researchers note that these hotspots are the same areas that have dealt with chronic underinvestment and that these areas are home to a higher proportion of lower median incomes.
Justin Huber, a doctoral student and research assistant at PSU, joins us to tell us more about this research and how identifying these high-risk areas can help cities approach more equitable emergency services and hazard mitigation.
Note: The following transcript was transcribed using AI and validated for accuracy, readability and formatting by an OPB volunteer.
Dave Miller: This is Think Out Loud on OPB. I’m Dave Miller. A recent study from Portland State University assessed the likelihood of four hazards in neighborhoods all around Portland: fire, urban heat, flooding, and landslides. The researchers found what they called “multi-hazard hotspots,” meaning areas that are at high risk of overlapping hazards, and they found that these hotspots clustered near I-205 in East Portland are in more diverse, more lower income areas. Justin Huber is a doctoral student and research assistant at PSU. He joins us now. It’s great to have you on Think Out Loud.
Justin Huber: Thank you.
Miller: What motivated you to do this study?
Huber: Yeah, my advisor, his name’s Heejun Chang. He’s done a lot of work around Portland in the past looking at the spatial distributions of individual hazards. He’s looked at things like flooding and extreme heat exposures throughout Portland, but really we wanted to try to recognize that people don’t just face one hazard, people face compounding hazards, things like flooding and heat may come at similar times or things like that. So we really wanted to try to move beyond just categorizing the disparity of one or two hazards and trying to recognize the totality of the hazards that people might experience.
Miller: And how did you settle on these four? I mentioned them before: fire, urban heat, flooding, and landslides.
Huber: We arrived at these four… a big part of it is related to the climate in Portland. We have a pretty seasonal pattern of precipitation. Most of our rainfall comes in the wintertime. So we wanted to try to recognize hazards across all four seasons, but really across the two main dividing lines between the wet and the dry season, that would be landslides and flooding in the wet season and then heat and wildfire in the dry season.
Miller: I take your point, those are all connected in some way to climate, but there are plenty of other concerns that could be really serious. I’m thinking about seismic vulnerability, you know, the big one, radon exposure, air quality from vehicle emissions or other things, smoke as well. How did you decide what not to include?
Huber: Yeah, that’s a tricky one, and a lot of it is related to the way that the hazards relate to each other. A lot of hazards are co-linear, is the statistical way to think about it, but they relate to each other. They show up in the same places, so they’re directly related to each other. So we really wanted to try to prevent using any that are directly related to each other.
One example of that is we only included pluvial flooding. It’s a type of flooding that refers to urban flooding on streets and things like that, when the storm drain network can’t handle it. Whereas other types of studies have looked at fluvial flooding, which is riverine flooding, when the Willamette overflows its banks or something like that, so really trying to identify one emblematic hazard that doesn’t necessarily directly relate to a lot of others that we included in the study,
Miller: And that maybe is the reason why smoke is not here, but fire is.
Huber: Absolutely. Yep. And smoke is definitely harder to track across the landscape. It’s more dependent on small scale variations in weather.
Miller: What did you find when you looked at all four of these hazards, mapping them together?
Huber: Yeah, the first big division is related to topography, sort of when you look at the west side of Portland, there’s a higher potential for landslides and wildfires in those sloping areas near Forest Park, areas like that, whereas in the east part of Portland, where it’s lower and flatter, there’s more potential for flooding and for extreme heat as well. But really the interesting part that we found was that there’s also areas where three or four of those hazards overlap, and those are the multi-hazard hotspots that we referred to earlier.
Miller: And what areas do have the most overlapping hazards? The majority of the ones we’re talking about, there were three, there’s a very small place that has all four of them, the most – I was gonna say unlucky, but maybe that’s actually not quite the right way to talk about, we can talk about causality in a bit – but when you look at the map, what stands out to you?
Huber: Yeah, you mentioned it. It really is that area of three, and then that small area of four, along I-205 in East Portland. That really is a confluence of, I hate to say a perfect storm, but a perfect storm of factors. There’s enough topographic variability to increase the susceptibility to landslides, but there’s also enough low ground areas for water to accumulate during flood events, all within a pretty small geographic space. And that really is what defines it, is that variation in that small space.
Miller: You’re able to look at the likelihood of all these four hazards, but also demographic data from census information. What were you finding when you looked at those two together?
Huber: Yeah, that’s a really important question. We don’t exist separately from nature. We exist within nature, and our social demographic traits are a result of nature and they influence our vulnerability to hazards as well. We found that most of these areas of high multi-hazard potential were on average a little bit more diverse. They had lower incomes and then higher proportion with the disability. And so a lot of those things are direct relationships to your ability to either evacuate or to recover from a hazard. For instance, if you have a disability, you may not be able to evacuate from a flood event as quickly or something like that.
Miller: It is worth pointing out, as you mentioned in passing, but just as we’re talking about income, for example, or race, that, as you’re saying, the areas with high levels of three hazards did cluster around I-205. But almost the entire west side, which has a higher median income and I think it’s more likely to be to be white, they were at higher risk for two hazards, so they’re not off the hook, but they were less likely to have the three hazards or the four.
I wanna talk about causality here. So, for example, are people with lower incomes living in these places because higher risk levels have kept property values lower and that’s where they can afford to find homes? Or is it the opposite, is less civic investment flowing to places where more marginalized people are living, leading to higher hazard levels? How do you think about “the chicken or the egg” here?
Huber: That’s a really tough question, especially in a large scale observational study like this. Since we’re not conducting a random controlled experiment, we can’t exactly assign directionality to these relationships that we find. One way that we tried to really unpack that question is, we looked at how the social and demographic variables changed over 10 years in those areas with high multi-hazard potential, those multi-hazard hotspots.
So what we found, the most pronounced there was that income growth was slowest in the areas with higher multi-hazard potential. That sort of suggests that there’s perhaps a depressing effect on income that relates from the natural hazards, but since we didn’t do a controlled experiment, we can’t assign directionality to that relationship specifically. But you just build pieces of the puzzle like that to try to build a compelling case for why there might be a causal relationship, even if you can’t prove it directly without conducting an experiment.
Miller: I want to turn to the implications of this. What do you see as the policy choices that could or maybe should follow from this study in the short term. What’s maybe low hanging policy fruit?
Huber: Yeah, absolutely. There’s definitely some low hanging fruit, and we talked about that a little bit in the manuscript. So there’s plenty more details if people would like to go read that there. But in the short term, the city of Portland, the Bureau of Emergency Management, puts out an evacuation plan that plots the evacuation routes and the destinations in relation to the FEMA – Federal Emergency Management – flood plains, basically areas that are likely to flood under certain storm scenarios. So the city could additionally overlay these multi-hazard potential spatial data layers, basically, to understand whether their evacuation routes are also resilient to the other hazards, urban flooding as well as things like wildfire and landslides.
Miller: What about longer term changes that you think this new map suggests?
Huber: Absolutely. So obviously, addressing social, large scale systematic inequalities is hard to do through something that’s got a small budget like an emergency management program. But what you can do is recognize some of those inequalities. You recognize that people in these hotspots might have lower income and might have a harder time recovering from these disasters. So you can put in things like wetlands that are found to be associated with lower multi-hazard potential to try to bring that down a little bit. You can also do some targeted programs. Like, if you find there’s a higher proportion of people who don’t speak English, you could do targeted outreach about evacuations and things like that.
Miller: Why are wetlands important?
Huber: It’s interesting. Despite their topographic position in the landscape, they’re very low, you’d think that they’d be associated with areas with high flooding. But they seem to have some ability to buffer and store excess floodwaters. They basically provide a relief valve in a way, where, if there’s flooding on the street, if there’s a wetland that’s been strategically placed, then they can just allow that wetland to fill with water, and take water that would have been on the landscape.
Miller: What are you most excited to be studying next?
Huber: Yeah, that’s a great question. I think that a big next step here is really to try to bring in… we didn’t explicitly consider redlining in this analysis. Redlining is the history of loan corporations not providing loans to areas that were deemed to have higher proportions of minority residents. And we didn’t explicitly consider that, but we found that a lot of the new development is occurring out east, over by I-205 in areas with higher multi-hazard potential, and in areas that were formerly redlined in central Portland, right along the east side of the river, things like that, are actually lower multi-hazard potential.
Miller: The lowest in the city, at least on the maps.
Huber: Yep, absolutely. And so it raises the concern that by incentivizing redevelopment in some of these low multi-hazard areas, you force out the residents that have been there for a long time onto higher multi-hazard potential where they might not be as able to respond to those hazards.
Miller: Justin, thanks very much. Justin Huber is a doctoral student at Portland State University and a research assistant for the Earth, Environment and Society major.
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