When temperatures soar, city dwellers feel the impact more than anyone else. The heat island effect can cause a city core to become as much as 20 degrees hotter than rural areas.

“More and more, it’s definitely an issue,” said James Hencke, a landscape architect and urban designer at David Evans and Associates. “The news is concerning about environmental issues. Those of us in planning and urban design, it is something (we) hear about.”

A variety of factors influence the extent of the heat island effect. Vivek Shandas, a professor in urban studies and planning at Portland State University who has studied the phenomenon since 2005, has found that temperatures around the city can vary by as much as 20 degrees, depending on tree canopy, surface types and colors of buildings.

“We have done empirical assessments when the airport is reporting 100 degrees and been able to capture temperatures (in other parts of Portland) ranging from 90 to 112,” he said.

The intersection of Southeast 82nd Avenue and Powell Boulevard, for example, tends to be one of the hottest areas in town, Shandas said. The worst heat islands tend to form in places with a lot of concrete, a high number of big buildings and few large trees, he added.

The people designing city infrastructure and buildings are responding by making adjustments to the kinds of materials they use.

“It’s something we think about,” Ric Battaglia, a project architect at Bora Architects, said. “For the most part, we try to meet or exceed LEED heat island standards.”

Leadership in Energy and Environmental Design standards are guidelines intended to minimize buildings’ impacts on microclimates as well as human and wildlife habitats. The goal is to prevent buildings (especially their roofs) from absorbing heat. When a building absorbs heat during the day, it radiates that heat out at night, increasing temperatures during cooler evening hours.

There are a couple of ways the roof of a building can meet LEED standards. At least 75 percent of the roof can be covered with reflective material, or at least 50 percent of the roof can be covered with vegetative material. If a combination of reflective material and vegetation are used, a total of 50 percent of the roof must be covered.

Architects also are changing building materials used on structures to keep cities cooler. For example, insulating materials can be used on exteriors and exterior shades can be installed over windows – all with the goal of reducing how much heat a building absorbs.

Buildings aren’t the only structures sending city temperatures climbing, though. Sidewalks and streets have long been identified as heat-absorbing culprits in cities.

“We can use different materials to make more reflective sidewalks,” Battaglia said.

Some cities have experimented with painting their streets with reflective materials. Los Angeles, for example, recently covering black asphalt with a material called CoolSeal. Hencke is among those tracking how the material functions a real-world situation.

“It’s fascinating,” he said. “That material is so white, I am curious about glare. It will be interesting to see how that works.”

Many methods of reducing heat have proven benefits, Hencke said.

“Heat island effect is one of the many issues we try to include in doing good planning,” he said. “Greening the city is one of the best ways.”

Greenery is one area where Portland excels. The city has 220,000 trees along streets and 1.2 million trees in parks, according to Jenn Cairo, an urban forester with Portland Parks and Recreation‘s urban forestry division. That number doesn’t include trees on private property.

Managing Portland’s urban forest gives Cairo an opportunity to help regulate temperatures throughout the city.

“It can determine where the priority for planting for trees is,” Cairo said. “How much shade is in that part of town? How much higher are the heat issues there? Trees are one of the most straightforward ways to mitigate heat.”

In the realm of building projects, mitigation of heat can be an important factor when seeking a building permit, Cairo said. In areas with a lot of asphalt and concrete, trees make a measurable difference in temperatures, she said.

Concerns about climate change and increasing occurrences of heat waves are expected to place a growing emphasis on how urban planning and design can be tapped to help keep cities cool.

“Ten-plus years ago … it was on people’s minds,” Hencke said. “Now, it feels like we have reached a point where city councils are demanding action. The planners were advocates, but the call to action wasn’t well received just 10 years ago.”

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