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How to redesign cities to withstand heat waves

Trees, green roofs, and white paint can help in a changing climate.

Families try to cool down at a public park in Portland, Oregon, during a heat wave in June 2021.
Maranie Staab/Bloomberg via Getty Images

As a record-breaking heat wave settled over the Pacific Northwest in June, a climate researcher named Vivek Shandas took a drive with his 11-year-old son and began to collect data. Using a handy infrared attachment for his smartphone, he measured temperatures across Portland as they hit unprecedented triple digits. He was amazed to find that temperatures varied by up to 40 degrees Fahrenheit from the exterior of one building to another.

Shandas, a professor at Portland State University, studies the wild variations in heat that you can find within a single city block. He is the director of the Sustaining Urban Places Research (SUPR) Lab at Portland State, which has received funding from the National Science Foundation, US Forest Service, and other federal agencies to study urban heat. He’s acutely aware that the ways we build can worsen extreme heat, and he looks for interventions that help cities survive heat waves as climate change makes them more common and extreme.

The past seven years have been the hottest ever recorded, and temperatures will continue to skyrocket without far-reaching government actions to curb greenhouse gasses. While countries are still falling short on slashing pollution, they’re already forced to help communities adapt to the rapidly altering climate. Heat is a particularly deadly stressor, and far worse in metro areas that have more concrete than greenery — which, in the US, often occurs in historically marginalized brown, Black, and Indigenous communities.

Shandas spoke to Vox about small but meaningful changes in how we build cities, from planting trees to creating ivy walls to painting buildings white. A transcript of our conversation, lightly edited for length and clarity, follows.

Local conditions can vary by 20 degrees — but they’re missing from most weather reports

Rebecca Leber

Are you seeing any misconceptions about this heat wave?

Vivek Shandas

We don’t really have a good way of describing the distribution of heat, street by street and down to the individual households, so that we can really start understanding the disproportionate effects. Historically, we just have one measurement of air temperature, often taken at an airport, that can really obscure the complexity of how heat is distributed across a region. We get this one monolithic number for a city when there’s about a 15- to 20-degree variation. In this heat wave, the high was registered officially as 115°F, but we were seeing places as high as 124°F in some neighborhoods of Portland.

The media has focused on this monolithic “heat island” concept, where the city is a different temperature than its surrounding areas. But changing the mindset from one temperature to hundreds of temperatures in a metro region is profound. It will mean we have some agency over how our regions grow and change.

If we’re thinking about how each street is a different temperature because of features that it has — building materials, color, trees, configuration of the buildings, orientation — that’s a profound insight in terms of getting better data and better evidence about distribution of heat. We ask the question: Why do we see one neighborhood that’s so much hotter than another neighborhood? In this case, a heat dome in the Pacific Northwest is mediated by the built environment. I don’t frankly see a lot of municipalities asking that question.

Rebecca Leber

How are you working to get better data at the granular level?

Vivek Shandas

There’s three ways to get data for heat.

  • Satellites: The sun sends down lots of energy-packed little waves that are called shortwave radiation that basically hits surfaces that absorb it, reflect it, or turn it into sugars like with trees and plants. Over time, they move that heat back out into the environment through long-wave radiation, so that’s something the sensors and the satellites can pick up. You can see these discreet differences between a parking lot and a lawn. If you’re walking, what you’re feeling on your skin is that mix of what the parking lot is emitting and what the lawn is emitting.
  • Stationary sensors: That’s why we need stationary sensors. Often, what I hear is there’s not enough resources to set up stationary sensors all over a metro region because it is cost-prohibitive, and maintenance is hard. The city, or more likely the state, will have stations set up in various places around a metro region — although there are often less than a dozen in most places with a population of 200,000, so there’s not a lot of granularity in terms of data.
  • Mobile data: It’s hard to make maps of street-level temperature, so we’ve started going out and collecting mobile “transects” in the morning, afternoon, and evening, and that’s giving us about 100,000 to 200,000 measurements over one hot day. With that, we can really start seeing what the individual street variation is.

How to cool a city without AC

Rebecca Leber

Planting trees to cool down cities and clean the air is a popular idea. Can the solution be that simple?

Vivek Shandas

I wish it were. It is an important part of the solution. We found that places that have more greenery are 15 degrees, even 20 degrees, cooler than areas that don’t have trees. Trees shade, they transpire water which also cools the surrounding environment, and they’re places of convening and collective connection during really hot days.

Just keep in mind that getting a tree into the ground is not necessarily the easiest thing to do, because it’s competing against utility lines, it’s competing against overhead power lines, it’s competing against driveways, parking, and sidewalks. Getting a tree into a place is often a very challenging proposition, especially in a highly urbanized environment. Trees are an essential part of the cooling formula, if you will, though they’re not the only one.

Rebecca Leber

How helpful are other interventions, like painting rooftops white to reflect heat or planting green walls and roofs?

Vivek Shandas

There’s a whole field of engineering that’s looking at highly reflective surfaces and how we engineer these so that they can really bounce back all of that heat to keep the area cool. There’s a lot of social implications of that, like whether people want that aesthetically and where, exactly, to apply this white surface — those are social and political questions.

We’ve often thought about green walls, or ivy on walls. I actually just went around Portland and took a bunch of pictures with my little infrared camera. The surface temperature of an ivy-covered wall in an industrial area was about 119°F. Right next to it was a non-ivy-covered wall, which was about 157°F — about a 40-degree difference in temperature that I could record with my camera.

That, to me, tells a story about the very few built-in features that buildings have to temper the heat. Not all streets and buildings are made the same, so we really want to find what solutions work well in specific roads, specific buildings, and specific neighborhoods. We’re continuing to redesign, build, and change our cities, yet with very little attention to heat.

That’s been my lifelong pursuit: How do we get developers, building codes, planners, landscape architects, and architects thinking about the ways in which heat is going to make this a harder place to live, even before we break ground on a building? Often what we’re seeing builders do now is throw AC at it.

Rebecca Leber

How can we build to withstand heat, then? Should there be some kind of requirement for builders?

Vivek Shandas

There’s no place that has a formal regulatory code requiring it. A few municipalities, like Portland and Chicago, have created codes for green roofs for buildings, mainly to address energy and stormwater.

Green roofs have benefits for tempering heat, because you have a layer of vegetation on a roof, which absorbs the heat, and — particularly if the vegetation is watered — it can really be a cooling effect. But often these are very high off the ground, so we haven’t found empirical evidence that green roofs are cooling that neighborhood. It’s much too high and much too detached from the everyday experience of a person walking on the road.

Chicago, Portland, and Boston created a kind of a voluntary checklist for developers to use as they’re designing buildings. Until some bigger movement happens at the federal level, I don’t think cities are necessarily going to be moving on this voluntarily, because there’s too much pushback from developers.

How to handle climate anxiety during a heat wave

Rebecca Leber

You’re right in the middle of this heat wave. How have you been riding it out?

Vivek Shandas

I never imagined that we would ever experience anything like this in the Pacific Northwest, at least for the next 10, 20 years. For it to arrive right now is a real surprise and shock.

I have an 11-year-old, and we’ve gone out during this heat wave and took photos with my infrared camera. We saw a group of houseless people right along a part of a busy street. I just took a picture of the tents that they were residing in, and those tents were coming in at 135 degrees. I was just absolutely floored. Your body has a very narrow range of tolerance for heat, and if you’re getting above 98 or 99°F, you run into some pretty serious thermo-regulatory concerns.

Rebecca Leber

How does it feel, on a personal level, to experience the effects of climate change on heat, the exact area you study?

Vivek Shandas

I have to go back to my 11-year-old. He asked me, “This is climate change, this is pollution, right, Papa?” And I said, “Yeah, very much.”

We’re going to see the climate change attribution studies that come afterwards, but it’s a very high probability that this is a 1-in-1,000-year event, in terms of the probability of such high temperatures in the Pacific Northwest.

My concern is, what is the best way to deal with anxiety and concern over future impacts? It’s to really think, what solutions, actions, and agency do we have to mitigate some of this, and to be sure we’re staying safe?

Part of the reason my son and I are going out and collecting these photos is to really start planting the seed that these are decisions we’re making, for buildings that are going to be here for 50, 70, or 100 years from now. Are we taking changes in our climate system into account when we are going about constructing and designing? That’s part of this exercise — just to see the idea that there are actions we can take.

Let’s get to some serious conversations about what those actions are, and what they might cost in terms of infrastructure, lives saved, productivity, and for learning in hot weather. Those are the kinds of seeds that we’re trying to plant with this work, and I need to do that for my own peace of mind and my ability to sleep at night.

Correction, July 1: A previous version of this story misstated Shandas’s affiliation with the Urban Resilience to Extremes Sustainability Research Network (UREx SRN) project.

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