Closed-toe shoes, knee-length pants, sun protection and a reusable water bottle to prevent waste. This is how more than 1,000 residents of the American city of Portland got to work last summer to remove cement tiles from the parking lot of the Morning Star Church. This is one of the latest interventions by the Depave movement, a grassroots organization dedicated to combating the deadly effects of urban heat islands by lifting concrete out of the ground.
Portland has a population of 635,000. Until recently, heavy and frequent rainfall was the only climate concern for residents and authorities. In recent years, however, intense heat waves caused by climate change have been added to this recurring social unrest.
Today, for example, amid extreme temperatures across much of the country, the city has surpassed 102 degrees, breaking the record of 100 degrees set in 1952, as confirmed by the National Weather Service. The scorching heat has killed 16 people across the state, most of them in the Portland metropolitan area. In total, more than 150 million people, coast to coast (45 percent of the U.S. population), are on alert, according to the scattered data by the National Integrated Health and Heat Information System.
The heat island and high mortality
High mortality rates, scientists and experts explain, are a direct consequence of the “urban heat island effect,” that is, the sharp increase in temperature in urban environments compared to surrounding rural or green areas. The Barcelona Institute for Global Health (ISGlobal) recently published a research in The Lancet about the close relationship between premature deaths and the phenomenon of the 'heat island', an abstract scientific concept but easy to observe: on high-temperature days, concrete retains heat during the day and releases it at night, making urban environments much warmer than greener spaces.
At the structural level, Portland has four factors that exacerbate this effect: dense, dark sidewalks and building materials; density and proximity of buildings; reduced vegetation cover; and high levels of waste heat from anthropogenic sources.
Sociologist Jan Voelkel studied the relationship between minority groups and urban heat in Portland. Their conclusion was that low-income communities are “disproportionately” exposed to the effects of climate change, in this case extreme heat. The reason? They live in areas with less tree canopy, more pavement, and less access to air conditioning.
Another researcher, Vivek Shandas, a professor of urban studies at Portland State University, led a nationwide heat mapping project in 2019. Of the 108 U.S. cities studied, Portland had the most dramatic difference between deprived and top-rated neighborhoods.
Faced with this reality, a group of neighbors decided to take action in 2008. With shovels, pickaxes and wheelbarrows in hand, they took to the streets to transform areas with excess paving into shared green spaces. Over time, the initiative has transformed into a successful citizen movement that is beginning to be replicated in other parts of the world.
Depave estimates that in 2008 it lifted some 33,000 square meters of pavement, the equivalent of four and a half football fields. Another figure that the makers are proud of: the 83 million liters of rainwater absorbed by the new vegetation that does not end up in the city's drainage system.
Currently, the organization has agreements with schools, religious communities, social organizations and small businesses to carry out urban ecology projects throughout the metropolitan area, ranging from the creation of a large natural park to the integration of several tree pits in a schoolyard to create more space. shade.
“Everything is teamwork. You don’t do anything alone, you always need someone else by your side. The efforts of the community are our greatest pride,” summarizes Katya Reyna, director of Depave, before any journalistic question.
Help from NASA
In the summer of 2023, Depave partnered with NASA through its Applied Sciences (Develop) program to measure the impact of the work performed. Satellite imagery confirmed that in the areas where the pavement was removed, temperatures dropped by an average of one degree Fahrenheit in the six cases analyzed.
Scientists have developed an urban heat map using a state-of-the-art thermal infrared sensor to capture Earth's surface temperature, and another heat vulnerability map.
The largest temperature variation occurred in a Primary schoolwhere the temperature had dropped more than 7.7°F.
According to the work’s lead investigator, Keegan Kessler, the data collected through remote sensing and geospatial tools “validate Depave’s efforts to reduce local urban heat.” The study also confirms that “heat in Portland is experienced unevenly” depending on the physical environment and sociodemographic factors.
As these new green spaces “mature,” their cooling effect will increase, Keesler hypothesizes. “The most interesting thing about this research is that it has given Depave quantitative support to communicate the impact of his work on heat mitigation at a local scale. The data are scientific support to inspire people around the world to get involved in local efforts for urban greening and climate justice,” the researcher emphasizes.
Contamination effect
Mariona Ferrandiz has a PhD in ecology from Claude Bernard Lyon University (France) and is a researcher at CREAF (Barcelona). A specialist in renaturalizing cities, she confirms what residents of Portland and many cities experience every summer: when temperatures are extreme, this heat island effect can be “very dangerous”: heat stroke, dehydration and excess mortality, as in Portland. The expert also adds that too much asphalt increases air pollution, because at high temperatures “volatile organic compounds are released.”
In this sense, citizen movements to remove cement are “a breath of fresh air.” Portland's success is even beginning to be replicated in other countries. In Ontario, Canada, it is working Green enterprisea nonprofit environmental education organization that promotes the creation of accessible green spaces. In 2012, inspired by Depave, they began removing concrete and replacing it with green, permeable surfaces.
“By removing paving and replacing it with green space, we increase the infiltration rate of rainwater, cool our neighborhoods, keep water clean by filtering polluted runoff, increase natural habitat for birds, bees and butterflies, and “give ourselves and our children a greater connection to the natural world,” its directors justify.
In total, this organization, with the help of more than 1,000 volunteers, intervened in fifteen urban spaces, removing 1,585 square meters of concrete in exchange for planting 2,850 native plants.
In the Netherlands, several municipalities have been competing in a so-called competition for three years Tile wipingwhich consists of removing as many tiles as possible from gardens and facades to replace the concrete with vegetation. In 2023, 28,067 tiles will have been removed (10,550 in 2022).