Researchers In Portland Study Urban Heat Island Effect
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.
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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