Climate Change and Green Space
A conversation with Professor Vivek Shandas on the role of the public realm in community resilience
Professor Vivek Shandas specializes in developing strategies for addressing the implications of climate change on cities at Portland State University. He is the founder and director of Sustaining Urban Places Research Lab, a cross-disciplinary lab with a policy-relevant approach to research, which includes the evaluation of environmental stressors on human health, the development of indicators and tools to improve decision making, and the construction of frameworks to guide the growth of urban regions.
As an interdisciplinary scholar, Dr. Shandas studies the emergent characteristics that generate vulnerability among communities and infrastructure. Following last summer’s intense heat waves, including a record-breaking heat event in the Pacific Northwest, we spoke with Dr. Shandas about the nexus of climate change, health equity and the built environment.
Why is it so important to understand how the built environment — including trees, concrete, asphalt, buildings and parks and public spaces — impact urban temperatures?
Dr. Vivek Shandas [VS]: I’ve spent the last 20 years thinking about how we design our cities and the implications of our design decisions on environmental health and wellbeing. As a species, we have designed our physical environment to reduce threats to us for millennia. So, while design that reduces threats from the environment isn’t a new idea, we had 35,000 years of a stable climate to understand how to reduce these threats. As we start to experience climate destabilization from what we’ve known for our entire evolutionary history as a species, we need to ask ourselves what our new climate will mean for habitable spaces and how we design them in the future.
In medieval times we were designing communities around the threat of attacking armies, which is why a lot of older European cities have big walls around them. As society modernized, we began to design spaces with asphalt and concrete, which caused runoff and necessitated gutters and underground pipe systems to channel stormwater into receiving bodies like rivers.
My research attempts to look at several aspects of the way we’re designing space at a micro-scale. I’m looking at sidewalks and the median next to the road, front yards, the geometry of buildings, to ascertain how people potentially get exposed to environmental insults. I’m also looking at how some spaces have higher temperatures, more air pollution, and a greater occurrence of flooding. The research is a biophysical assessment of the built landscape, grounded in issues of social justice and equity — understanding why some people in cities have access to less polluted spaces, who has access to the green spaces and what kind of decision-making has historically reduced people’s access to a healthy environment.
What have you learned about the impact of green spaces on urban temperatures and public health?
VS: Temperatures are the piece of my research that has been emphasized recently, given the deadly “heat dome” that descended on the Pacific Northwest last June. It’s getting attention because the temperature is immediate and meaningful to everybody. Most of us think about temperature in the context of illness — a high temperature means something is wrong. Humans also understand intuitively what it means to be in a hot place versus a cool place. As a result of looking at temperatures over time, I have learned a lot about how the built environment mediates exposure to hotter and cooler spaces.
One of the most interesting aspects of urban temperatures is that there are multiple factors that influence how hot different areas in one place are. For example, the amount of green space and big trees is a big factor in heat variance; areas with trees are much cooler than areas without trees by 10 or even 15 degrees. Trees cool spaces by giving us shade and transpiring water.
However, trees are living biological entities that need a lot of care and feeding. Even older, well-established trees are being impacted by the hotter temperatures, which really concerns me. Green space and tree canopy are among our first and most formidable defenses to rising temperatures. Planted and cared for well, they could help entire cities cool down over time. Unfortunately, we’re not yet doing much thinking as a society about how trees could help reduce temperatures. We’re not building spaces that are hospitable for trees and vegetation.
How can green spaces — and the in-between spaces like medians and the land in front of buildings — support us as climate change intensifies?
VS: Green spaces can support us in myriad ways. In addition to providing shade and transpiring water that cool us, they have clear impacts on air quality and atmospheric conditions. They pull in pollutants up through their stomata (Editor’s note: stomata are minute openings found in the epidermis of leaves, stems and other plant organs) and absorb the particulate matter in pollution that is deposited on the surface of leaves or branches, leaving the air cleaner. When it rains, the trees and plants absorb the water that falls from the sky, reducing the potential for flooding events. I think of them as the “lungs” of a city, helping us live in much more healthy environments.
Research shows that our emotional state is really affected by trees, especially foliated trees. They lower blood pressure, they calm our nerves. We’re coming to understand there is a symbiotic relationship between most animal species and the trees that surround them, and humans are one of those species.
Green spaces and trees also support overall community health. Neighborhoods that have trees have higher home prices. Green spaces have been for millennia and remain today places of social gathering and convening, bringing communities together. There’s research that shows places with trees have fewer traffic accidents, calming drivers as they move through neighborhoods.
We know that areas with a lot of greenspace and trees can have reduced electricity bills during the summer and the winter since trees hold in heat when it’s cold. You run your AC a lot less when you’re surrounded by trees, which reduces greenhouse gases.
Could green spaces be a place of refuge as climate impacts intensify?
VS: Some studies looking at baby birth weight and gestational age seem to show access to green spaces gives new mothers a better ability to manage a very stressful time in life. Green and treed spaces hold the potential to calm and comfort all of us during stress — and climate change is sure to bring stress at both an individual and a community level.
During the “heat dome” event in Portland, it was 14 degrees hotter than the city’s highest-ever temperature in recorded history. Because I have been studying urban temperatures through sensors placed in different neighborhoods around the city for many years, we were able to record the temperatures across a diversity of places during that catastrophic event.
What we noticed was that neighborhoods that had more trees were far cooler than the hottest neighborhoods and these differences were exaggerated in the extreme temperatures. For example, in the past we had found that on a 90-degree day, the difference between a neighborhood with trees and one without was upwards of about 15 degrees Fahrenheit. During the heat dome, that difference increased dramatically — as the temperatures went up to 116, there was a 25-degree difference between neighborhoods. That got our attention!
As climate change accelerates and intensifies, we’re going to have to face the idea that people who live with shade are going to experience fewer impacts than people in communities without shade. We’re also going to see the same with flooding events, as trees absorb and capture water in some places while areas without trees fare much worse.
What do you know about the nexus of race, income and urban heat islands? How have redlining and other racist practices contributed to a public realm that doesn’t protect residents from urban heat?
VS: Redlined areas have historically been the places where less desirable land uses were the norm: big freeway projects, industrial sites, manufacturing sites, and places with large parking lots, like big box stores. These are things that wealthier neighborhoods do not want, and as a result, the places that have the lowest land rent value — places where disinvestment has happened for decades — often attract them.
These lower rent places are not a coincidence. They occur as a result of land-use planning decisions that go back to the beginning of the country, decisions governing where certain kinds of development could happen. There’s a number of different power structures at play, but ultimately what happens is that redlined and disinvested areas end up with the less desirable land uses, the freeways, the big box stores.
These big freeways, these big box stores, these industrial facilities were located in lower rent areas which by design have lots more solar absorbing materials: buildings made of concrete, asphalt from parking lots and the freeways. These really dense materials retain the heat from the sun for long periods and radiate it back out into the environment. This heat can amplify over time and then a specific area gets much hotter in terms of surface temperatures and air temperatures. And what we end up seeing is that these big developments went into places that were less invested. We’re left with a legacy of racist infrastructure projects that now amplify temperatures in many redlined neighborhoods.
We wrote a paper in 2020 that looked at 108 cities across the country to see if areas that were historically redlined were hotter today than their “greenlined” (where the financing system invested capital) counterparts. We found that in redlined neighborhoods across 94 percent of the cities we looked at were about five degrees Fahrenheit hotter on average. Some were as high as 13 degrees hotter than their greenlined counterparts. That got me thinking seriously about the insidious segregation of neighborhoods because of specific socio-demographics. As climate change intensifies, the communities that weren’t resourced back in the early 20th century are now bearing the brunt of this climate dysfunction.
This has turned out to be a life-and-death situation. In 2009 my research identified urban heat islands across the city of Portland, mostly in low-income neighborhoods. We knew that those places identified more than 10 years ago were where people would experience the most dangerous physical heat. When the heat dome brought temperature above 110 degrees (a temperature most people in Portland didn’t think was possible), these were the places that the most number of people died (Editor’s note: hundreds, if not thousands, died in the June heat dome event.)
It’s not that hard to identify where heat will hit community members the hardest, so we need to prepare for it as it comes on really quickly over a very large geography. It definitely impacts those who are the most vulnerable in our communities in part because we designed their neighborhoods to be really hot.
What can cities do right now to the landscape to be more resilient to extreme heat? And what should they be doing in the coming years through changes in policy and practice to mitigate this risk?
VS: There are both the physical built environment solutions and community responses. We’re going to need lots of different solutions because there is no silver bullet solution to climate change. We need to do multiple things at once.
The physical environment solutions are about green, gray and blue infrastructure. It’s not just about planting trees, even though I believe they will be an essential frontline in cooling neighborhoods. That’s because in addition to the questions about the trees getting the right care and governance of public space, green infrastructure in this country goes largely into wealthier neighborhoods. It costs a lot to tear up concrete to plant a tree in a neighborhood that’s mostly paved, and there are greenhouse gas impacts in tearing out concrete. Green infrastructure has some bottlenecks, so we need more options.
Blue infrastructure is about capturing the water that falls on cities in ways that don’t push the water out right away. It’s how we capture and collect water in cities because as climate change intensifies, water is going to become an even more precious resource. Given the United States’ love of big infrastructure, I think large water capture and collection systems could be very popular across political divides. Another promising practice around the country is the creation of decentralized ‘bioswales,’ small areas of green space established to capture stormwater. Because they often have trees and shrubs, they reduce the amplification of heat. Placed with enough density and if well-maintained, these can cool neighborhoods, improve the aesthetics, and provide a host of benefits to birds and other creatures with whom we share our cities.
The gray piece is about ensuring our existing infrastructure systems are able to withstand accelerating climate impacts. An example of this is Portland’s light rail and streetcar transit systems, which had to shut down during the heat dome because the physical infrastructure that supports the system failed. We need to assess our infrastructure and systems to understand what can withstand the extreme cold and extreme heat that is coming.
Finally, we need to be thinking strategically about development that is amplifying temperatures in our cities. I do not know of a U.S. city that is revising codes, regulations, and/or standards to mitigate rising temperatures, even though we have robust research about building materials, development configurations, coloring, and types of landscapes that can help to turn down the heat. For example, ‘heat overlay zones’ allow scrutiny of new development or redevelopment of the heat mitigating actions that are put into place. Requiring developers to provide evidence about how their proposed development will mitigate temperatures will be essential. We already have such policies for stormwater and air pollution, yet public policies for mitigating climate-induced heat stress are still woefully inadequate. We have a lot of work to do, but I believe through collective action to reduce exposure to extreme heat, we can be more resilient in the coming years.
Reimagining the Civic Commons is a collaboration of The JPB Foundation, the John S. and James L. Knight Foundation, The Kresge Foundation, William Penn Foundation, and local partners.
