“ One of the biggest takeaways from this work is that in the places we live, work and play, the construction materials, colors, amount of roadways and greenery — decisions that are largely left to city planners — have an effect on the varying temperatures we experience in Portland. We have control over the design of our cityscapes. If summers are getting hotter, shouldn’t we be considering how different built designs impact local temperatures? Nature based solutions such as the ones described in the study — when applied effectively and used in combination — can reduce temperatures of even the hottest places.”
Researchers In Portland Study Urban Heat Island Effect
July 10th, 2019 by Steve Hanley in Clean Technica
We have all heard people say it is hot enough out to fry and egg on the sidewalk. In some cases, that is literally true as the sun beats down on asphalt in the summer. You may also have heard of the “heat island” effect that affects many cities. In essence, it means the streets, sidewalks, and rooftops of the city get so hot during the day, they can’t give back all the heat they retain after the sun goes down overnight.
Credit: Atmosphere under CC BY 4.0 license
That means they start the next day already hotter than they should be before the process starts all over again. People in sunny places like Phoenix, Arizona are well familiar with this phenomenon. The problem is that architects and city planners pay little attention to heat shedding strategies. This not only drives up the cost of air conditioning, it also has adverse effects on the health of the elderly, young children, and people with respiratory ailments.
Researchers at Portland State University in Oregon examined a number of strategies to reduce the heat island effect and published their findings in the journal Atmosphere recently. Led by Urban Studies and Planning Professor Vivek Shandas, the study used computer modeling to show the temperature differences that can be made in a variety of property types — from tree-filled neighborhoods to heavily-paved industrial areas — through planting trees and vegetation, installing green roofs, and using materials on roofs and pavement that reflect heat.
According to an article by Science Daily, the biggest differences occurred using reflective materials and planting trees. Although real world testing will be needed to verify the computer modeling results, Shandas says green roofs provided localized cooling of the roofs themselves, especially when watered. They also provide other environmental benefits such as retaining storm water, controlling pollution, and providing a habitat for wildlife.
Conversely, cutting down trees and paving over the land where they once stood can increase the temperature in that area by 25º F on a sunny day. That increase in heat spills over into surrounding neighborhoods. Cue Joni Mitchell’s Big Yellow Taxi.
The study was done at the request of the City of Portland and may be used by city officials as a guide for future planning and development. The work includes an interactive map showing every parcel of land parcel in the city, its pollution index level, and percent of vegetation canopy.
“One of the biggest takeaways from this work is that in the places we live, work and play, the construction materials, colors, amount of roadways and greenery — decisions that are largely left to city planners — have an effect on the varying temperatures we experience in Portland,” Shandas said.
“We have control over the design of our cityscapes. If summers are getting hotter, shouldn’t we be considering how different built designs impact local temperatures? Nature based solutions such as the ones described in the study — when applied effectively and used in combination — can reduce temperatures of even the hottest places.”
A corollary is that heat trapping systems like the aerogel invented recently by scientists at MIT could be used to put that heat to good use in the winter to heat the interior of buildings without burning fossil fuels. Heat management will be a vital part of designing the sustainable cities of the future.
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Planting more vegetation, using reflective materials on hard surfaces and installing green roofs on buildings can help cool potentially deadly urban heat islands — a phenomenon that exists in nearly all large cities — a new study from Portland State University shows. Those solutions, however, present a growing challenge to developers and planners as neighborhoods become increasingly dense and single-family homes give way to apartment buildings.
Led by Urban Studies and Planning Professor Vivek Shandas and published in the May 21 edition of the journal Atmosphere, the study used computer modeling to show the temperature differences that can be made in a variety of property types — from tree-filled neighborhoods to heavily-paved industrial areas — through planting trees and vegetation, installing green roofs and using materials on roofs and pavement that reflect heat.
The modeling showed that the biggest differences came from using reflective materials and planting trees. Shandas said green roofs provided localized cooling of the roofs themselves, especially when watered, but that they needed to be studied further before they could be considered as a broader solution for urban heat. He noted, however, that green roofs provide other environmental benefits such as retaining storm water, controlling pollution and providing a habitat for wildlife.
The study was done at the request of the City of Portland, and may be used by city officials as a guide in Portland’s planning and development. The work also includes interactive maps showing every land parcel in the city, their pollution index levels, percent of vegetation canopy and more.
“One of the biggest takeaways from this work is that in the places we live, work and play, the construction materials, colors, amount of roadways and greenery — decisions that are largely left to city planners — have an effect on the varying temperatures we experience in Portland,” Shandas said. “We have control over the design of our cityscapes. If summers are getting hotter, shouldn’t we be considering how different built designs impact local temperatures?”
The phenomenon of higher temperatures in areas with a lot of buildings and pavement is known as the urban heat island effect. Previous studies by Shandas and others show that urban heat islands are associated with higher pollution and negative health conditions, especially for the elderly, young children and people with lower incomes.
While testing solutions that reduce urban heat, the study also showed the effects of doing the opposite. For example, it showed that paving over places that previously had a lot of tree canopy could raise the temperature as much as 25 degrees Fahrenheit on a summer day. Nearby neighborhoods would experience a spillover effect.
“Nature-based solutions such as the ones described in the study — when applied effectively and used in combination — can reduce temperatures of even the hottest places,” Shandas said.
Story Source:
Journal Reference: Yasuyo Makido, Dana Hellman, Vivek Shandas. Nature-Based Designs to Mitigate Urban Heat: The Efficacy of Green Infrastructure Treatments in Portland, Oregon. Atmosphere, 2019; 10 (5): 282 DOI: 10.3390/atmos10050282
Results were inconsistent across landscapes, and showed that one mitigation solution alone would not significantly reduce extreme heat. These results can be used to develop targeted, climate- and landscape-specific cooling interventions for different land uses, which can help to inform and refine current guidance to achieve urban climate adaptation goals.
Portland State University. “How to reduce extreme heat in city neighborhoods.” ScienceDaily. ScienceDaily, 8 July 2019. <www.sciencedaily.com/releases/2019/07/190708154042.htm>.
