A massive tri-county heat mapping project has confirmed that summer temperatures vary widely across the metro region – with the hottest temperatures experienced by people living in suburban areas near highways.
The new data, unveiled Wednesday by Multnomah County health officials, shows how the built environment – the amount of pavement, proximity to highways and number of trees – can increase or decrease the temperature in a neighborhood during the summer, potentially leading to different health outcomes.
The mapping – the most precise and wide-ranging to date – will help Multnomah, Washington and Clackamas counties and community organizations better prepare for extreme heat events and reduce risks among the most vulnerable residents, public health officials said. Heat waves are especially dangerous to older people, low-income people, people with disabilities and people of color, health officials say.
One stark finding: Across the three-county area, there was a 17-degree difference between the hottest and coolest places on the afternoon of July 22, 2023, the day that volunteers collected readings.
The highest temperature was recorded in Tualatin, at 92.1 degrees, while the lowest was in Portland’s Forest Park, at 77.6 degrees.
The high that day, according to the National Weather Service, was 89 at Portland International Airport.
The hottest areas had fewer trees, more hard surfaces like roads, rooftops and parking lots and sprawling development patterns, said Brendon Haggerty, a manager with the Multnomah County Health Department. The coolest areas were parks and rural forested areas.
“For some people that can be the difference between life and death or going to the emergency room, or feeling safe and cool enough in your home,” Haggerty said.
According to the collected data, Multnomah County’s hottest cities are Wood Village, Maywood Park and Fairview. Portland’s hottest areas are near Lents, Mall 205 and industrial areas near Portland International Airport.
Washington County’s hottest areas include parts of Sherwood, Tualatin and Cornelius. And Clackamas County’s hottest cities are Molalla, Canby and Wilsonville.
The heat mapping campaign aimed to identify heat-related risks on the heels of the 2021 heat dome, which killed dozens of people in Multnomah County and sent hundreds to the emergency room with heat-related illnesses.
The project builds on previous efforts to understand how extreme heat varies by neighborhood in the metro area. It’s part of a nationwide effort to map urban heat islands – areas that experience the most harmful health effects of rising temperatures.
More than 100 volunteers drove predetermined routes three times a day across the three counties on July 22, collecting temperature and other readings via a special sensor affixed to their cars.
They collected more than 269,000 temperature readings, covering over 400 square miles. The data was then crunched and a map created by CAPA Strategies LLC, a Portland-based climate consulting firm that partners with the National Oceanic and Atmospheric Administration to map heat islands around the U.S. and the world.
Portland had the highest range between coolest and hottest places of all of the cities, a 14.1-degree difference. Its lowest temperature recorded was 77.6 degrees on the northern edge of Forest Park and the highest 91.7 degrees in the Hazelwood neighborhood, off Northeast 102nd Avenue and Northeast Glisan Street.
Previous heat mapping efforts in Multnomah County relied on satellite remote sensing to map land surface temperatures and estimate community risk. The heat mapping campaign, on the other hand, recorded ground-level temperature, which is a lot more precise, Haggerty said.
The mapping campaign’s results will inform actions by the three counties on emergency management, land use planning, tree planting, housing and transportation, among others, he said.
The new data will be used to update Multnomah County’s Heat Vulnerability Index, an interactive tool that displays how heat vulnerability, sensitivity and exposure affect people’s ability to adapt to extreme heat by census tract or specific address. Clackamas County and Washington County will use the new data to inform their Climate Adaptation plans and emergency response plans.
County officials said healthcare and outreach workers can use the new heat map to prioritize people who are most at risk during extreme heat and alert residents to make plans for hot summer days.
Translated versions of the hottest areas identified in the project will be available in the coming weeks.
In the future, the counties also can add other data layers, including the type and age of buildings, the number of trees in a neighborhood and estimates that a home has an air conditioner – all in the effort to identify which populations and neighborhoods are at greatest risk from extreme heat and in need of more help.
— Gosia Wozniacka covers environmental justice, climate change, the clean energy transition and other environmental issues. Reach her at gwozniacka@oregonian.com or 971-421-3154.
If you purchase a product or register for an account through a link on our site, we may receive compensation. By using this site, you consent to our User Agreement and agree that your clicks, interactions, and personal information may be collected, recorded, and/or stored by us and social media and other third-party partners in accordance with our Privacy Policy.
