18.–21.05.2022 #polismobility

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How trees in urban areas protect against heavy rain and promote biodiversity

Islands of greenness

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Urban green islands protect against heavy rain and promote biodiversity. In 2019, 35,000 m² of urban space in Copenhagen was converted into a green stormwater protection area.

Urban Green Islands_Sankt-Kjelds-Square and Bryggervangen © Mikkel Eye

Urban Green Islands_Sankt-Kjelds-Square and Bryggervangen © Mikkel Eye

If you look at the before and after pictures, you will hardly recognise the surroundings around Copenhagen's Saint Kjelds Square and Bryggervangen Street. After three years of realisation, an extraordinary transformation project was completed there in 2019. Commissioned by the City of Copenhagen, the architectural firm SLA redesigned around 35,000 m² of urban space, including around 25,000 m² of streets and asphalt surfaces, into a green stormwater protection area as part of the "Climate District" initiative. For this purpose, 586 new trees were planted, to which the water is directed during heavy rainfall and can slowly seep away.

Green spaces also contribute to reducing air pollution and the urban heat island effect. The main reason for the phenomenon that the ground temperature is higher in urban agglomerations than in rural areas is the high proportion of built-up and sealed surfaces, but also air pollutants. Increasing the amount of green space in cities can counteract this effect. Biodiversity and city dwellers also benefit from the transformation - offering a nature experience with quality of life in the middle of the city.

Planting trees as protection against flooding

Urban Green Islands_Sankt-Kjelds-Square and Bryggervangen © Mikkel Eye

Whether to linger... © Mikkel Eye

The project focuses on planting 586 new trees of 48 native species in the middle of the city. These were planted on specially designed green urban areas and serve efficient stormwater management. The city has faced increasing amounts of heavy rainfall in the past, resulting in overflowing sewers. As a network of green "rain gardens", the new plantings are supposed to be able to absorb even the heaviest rainfall. The water is transported to the trees and can thus seep away on site or, alternatively, reach the port directly via a pipeline. In this way, the water is used as a resource and helps the plants to thrive in the urban space.

Nature experience in the middle of the city

Urban Green Islands_Sankt-Kjelds-Square and Bryggervangen © Mikkel Eye

... or for sporting activity: urban green islands not only benefit the microclimate, but also the quality of life. © Mikkel Eye

In addition to their protective function, the newly created green spaces also allow for alternative and, above all, communal use. They serve as social meeting places and offer space for new activities. People can stroll between the trees and let nature take its effect on them, discover new native plant species: a completely new experience right on their doorstep. Numerous seating areas invite people to spend time outside, lying tree trunks offer children opportunities to play and climb. The new green spaces also attract other species - insects, for example, find a new home here.

SLA have created a new urban nature that is not only functional, but also aesthetic, diverse, adaptable and community-friendly. The residents find a new green space directly in their neighbourhood, which both pursues necessary climate adaptation measures and contributes significantly to the beautification and enhancement of the urban environment. The project shows: Protection from heavy rainfall can go hand in hand with a green and relaxing urban space, while at the same time strengthening biodiversity.