What can Rotterdam teach about the power of green roofs

From May 26 to June 26, the Dutch city of Rotterdam is showcasing the potential of rooftops. The Rotterdam Rooftop Walk connects rooftops through air bridges, offering a vision of the future of cities.

“Often, cities offer little space to develop more green spaces, and rooftops provide that space for plants and for biodiversity,” says Léon van Geest, director of the Rotterdam Dakendagen Festival.

Green rooftops can be an effective solution to urban heat islands, cities or specific neighbourhoods within an urban area that have become much warmer than their surroundings due to absorbing and re-emitting the sun’s heat. Disenfranchised urban areas are particularly struggling with heat: A 2021 study in the Nature Communications journal found that heat exposure tends to be higher in lower-income neighborhoods, both in the U.S. and globally. Residents of these neighborhoods are also less likely to have air conditioning, or may be unable to afford to use it even if they do have it. This heat exposure aggravates inequality through risks such as higher heat-related mortality, heat strokes, dehydration, loss of labor productivity and decreased learning capacities, while also increasing costs for air-conditioning.

Enter green rooftops. They can take many shapes — lush gardens, potted plants, solar panels, urban farms, wildflower meadows and community spaces painted in light colors that absorb less sunlight — and can help combat heat islands in several ways. Plants and even trees on the roofs of buildings can drastically lower the urban heat island effect by reducing temperatures. According to the EPA, citywide ambient temperatures can be lowered by 5 degrees Fahrenheit with green roofs, reducing building energy use by up to 0.7 percent and thus lowering energy demand. Green roofs can also retain water and thereby prevent or reduce urban flooding. They filter greenhouse gas emissions and other pollutants from the air and attract more biodiversity.

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