In the middle of a heat wave this month, Portland State University researchers Vivek Shandas and Jackson Voelkel drove across the city of Portland with a thermometer sticking out the window.
The thermometer was connected to a GPS unit. Together the two devices logged the temperature and location every second as the car moved along city streets. As they drove past the Portland International Airport, Shandas noted lots of asphalt and a near total lack of trees.
“This is one of the hottest places in the city,” he said.
He knows that because the thermometer on his car is telling him something the Weather Channel can’t. It’s tracking the temperature differences from one block to the next at the street level – where people actually feel the heat.
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He and other PSU researchers have spent years developing heat maps of Portland’s neighborhood temperatures based on numerous traverses across the city. In a heat wave, they’ve found a 15-degree difference between places like the airport and a forested park.
“And that can be the difference between a person’s well-being in one part of the city and really quite fatal in other parts of the city depending on where you are,” Shandas said.
They’re looking for ways to cool these places down and reduce the health risks residents will face in the hotter summers to come with climate change. The strategies range from opening more cooling centers with air conditioning during heat waves to strategically removing pavement and adding trees.
The Health Risks Of Urban Heat Islands
More than half of the average city landscape is covered in dark, sun-absorbing surfaces such as asphalt or dark roofing, according to the Heat Island Group at Lawrence Berkeley Labs. Those surfaces can get 60 to 70 degrees hotter than more reflective surfaces and radiate heat day and night, creating what’s known as an urban heat island.
Tim Lynch, a policy analyst for Multnomah County, says with climate models predicting hotter summers and more extreme heat events, he sees more health risks for people living in these urban hot spots.
The heat alone poses health risks from dehydration – to the elderly, homeless and low-income people and those with heart disease and diabetes. But it also creates another problem: It cooks air pollution into ground-level ozone, or smog.
“That’s why we say urban heat islands are a double-whammy for people’s health,” said Kari Lyons Eubanks, a program specialist with Multnomah County Health Department. “The hottest places in the city are also more polluted. You add climate change to the mix, and the risk of heart attacks and strokes and asthma attacks are even higher.”climate change response plan to the test.
“Here we are. We’re in the changes,” Lyons Eubank said. “I think the hotter, drier summers have come more consistently and have come quicker than maybe we had originally thought. We really are in the phase of: What does it mean to adapt to this?”
Finding The City’s Hottest, Dirtiest Places
One way to reduce the health risks of extreme heat exacerbated by urban landscapes is to make city neighborhoods a little cooler. But which neighborhoods need the most attention? And what’s the best way to cool them down? This is where Portland State’s new interactive map – combining heat, pollution and population data – comes into play.
The first layer of the map outlines the city’s urban heat islands, developed using detailed temperature measurements from the researchers’ traverses across the city. By comparing block-by-block temperature data with the amount of trees and greenery versus dark rooftops and pavement along their traverse routes, researchers developed a formula they could apply to the whole city to determine whether some neighborhoods run hotter than others.
The maps show a big, blue cool zone in Forest Park – the city’s 5,100-acre urban forest – and a big, red hot zone all along the Columbia River near the airport.
Shandas said he hopes this will be the key to helping cities adapt to hotter summers. He clicks several boxes on the interactive map to find out which of the city’s hottest neighborhoods have a high percentage of older adults with pre-existing health conditions and no air conditioning.
“So we can identify specific areas that might be most vulnerable to these heat waves,” he said. “We’re trying to characterize the hottest, dirtiest places where people live in the city and then what actions can be taken in those specific locations.”
Cooling Down The Hot Spots
Local officials say they are looking at using the data for more than informing where they site cooling centers and drinking water distribution hubs when the weather heats up. They may use heat-island mapping data to redesign the hottest neighborhoods by cooling them down.
According to Michelle Kunec-North with the Portland Bureau of Planning and Sustainability, the mapping program could help the city consider removing pavement and adding trees to mitigate the urban heat island effect.
“Where can we invest in bioswales or tree-planting and preservation? Are there buildings that might offer shade in the future?” she said. “What this information can do is help us think more strategically and at a much finer scale about where we can apply those strategies to make the most difference.”
The mapping program is still in development, Shandas said, but it will eventually be publicly available so neighborhood groups can use it to plan their own cooling efforts.
“What would the community need to do?” he said. “Can they paint the pavement white to absorb less heat? Do they create social programs? Part of this is about being proactive. Knowing that there’s a heat wave coming, what could we actually do short term and long term?
“All over the world we’ve seen massive heat waves that have killed tens of thousands of people. We don’t want to be one of those cities that actually sees high numbers of deaths occur from urban heat or poor air.”