The urban heat island (UHI) effect threatens the well-being of people living in cities of all sizes. During a heat wave, the UHI can even threaten the lives of vulnerable people, such as older adults. So, cities are starting to get serious about tackling this threat.
Portland is an example.
Depave. As the name suggests, Depave is an initiative that was launched in 2008 with a clear goal: replacing pavement with green space in historically disadvantaged areas. Recent projects include a nearly 18,000-square-foot parking lot next to a church last year and the renovation of a downtown intersection.
The neighborhood initiative has received support from NASA to evaluate the impact of its projects.
UHI. Cities tend to retain more heat than small towns due to several factors. First, there are some building materials that absorb and store heat. Furthermore, cities tend to have poor ventilation because of street grids that stop wind currents. There are also numerous heat sources in the cities, such as vehicles or air conditioners.
Usually, this isn’t a problem, but the UHI effect can play a critical role in increasing the mortality associated with these phenomena during heat waves. In general, the heat island effect can reduce our thermal comfort. In other words, it can make us feel hot.
Working with NASA. The parking lot and intersection projects aren’t the only ones Depave has undertaken in Oregon’s most populous city. Evaluating the impact of these initiatives is challenging, so Depave enlisted NASA’s help.
The study was conducted as part of NASA's applied sciences DEVELOP Program and led by researcher Keegan Kessler. Using tools such as the Thermal Infrared Sensor (TIRS) and Operational Land Imager (OLI) on the Landsat 8 satellite, Kessler and her team estimated temperature reductions at sites with Depave projects.
The team analyzed six projects, estimating an average temperature reduction of 33 degrees Fahrenheit. According to the city of Portland, the maximum reduction measured was 40 degrees Fahrenheit.
Depaving Portland. The local government is one of the entities that has partnered with the Depave initiative through the Portland Clean Energy Community Benefits Fund (PCEF). According to the fund, the initiative has succeeded in depaving more than 360,000 square feet in the city since 2008.
More than heat. In addition to thermal advantages, removing pavement from surfaces can provide other benefits, particularly when it comes to water management. Paved surfaces generate runoff, which means that precipitation that falls on them doesn’t filtrate into the ground but runs off. Cities have catchment systems that aim to capture this water.
Portland’s pavement removal efforts have reduced the need for urban system water capture. According to PCEF, their efforts have diverted approximately 24.5 million gallons of rainwater from storm drains yearly due to the increased filtration of environments without pavement.
This article was written by Pablo Martínez-Juarez and originally published in Spanish on Xataka.
Imagen | Elle Hygge/Depave | NASA
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