Climate action (adaptation and/or mitigation)

The Republic Services Garden is a one-acre garden created and located in Hance Park, a large urban park located in downtown Phoenix, Arizona. As part of the larger revitalization of the park, the garden was created to showcase native desert plants, recycled materials, and shaded seating, serving as a model for eco-friendly urban landscaping. Its key goals are to enhance the park's appeal, create a welcoming community space, and demonstrate the potential of sustainable design in cities. By blending nature with urban infrastructure, the garden helps mitigate the urban heat island effect, addresses water scarcity, and supports habitat restoration. The project is a collaboration between the City of Phoenix and the Phoenix Parks and Recreation Department, with financial backing from Republic Services, the second-largest waste disposal company in the U.S. (Refs. 1, 5, 7, 12, 15).

The Africatown Heritage House Bioswale is a gently sloping green space with multiple functions which include catchment of runoff water and filtration of pollution in the runoff water (Ref 2), erosion control (Ref 2), and creation of habitat for biodiversity (Ref 1). It also has an educational purpose for students and the local community (Ref 2) and contributes to overall beautification (Ref 5).
The Bioswale was built by Birmingham-Southern College’s Environmental Center (Ref 6) and developed through the collaboration between the Mobile County Commission, the Mobile Area Lodging Association, Mobile County Training School, Mobile County Training School Alumni Association, and the National Academies of Science (NAS) Gulf Research Program (Ref 2). The project aims to address heavy rainwater management (Ref 5) and drainage issues (Ref 3).

Reforestation project for the "Cerro de la Popa", which is Cartagena's highest point and one of the main tourist attractions because of the view and its colonial convent (Ref 6). The hill currently faces illegal occupation and environmental deterioration caused by deforestation, poor solid waste management, burning, logging, and the loss of vegetation cover (Ref 4, 5). The intervention in La Popa consists of reforestation activities, environmental education activities with children, and awareness-raising activities with adults about caring for fauna, flora, and water bodies (ref 2, 3). SSince 2020, the Establecimiento Público Ambiental (EPA Cartagena) has led the recovery initiative, prompted by the urgent need to counter the increasing encroachment by migrants and vulnerable populations (Ref 4). The project comprises reforestation efforts, environmental education sessions with children, and community outreach to raise awareness among adults regarding the protection of local fauna, flora, and water bodies (Refs 2, 3). As part of a broader municipal agenda, the initiative remains active, with the most recent intervention conducted on July 11, 2024 (Ref 2).

Detroit’s neighborhoods grapple with a dual challenge: neglect and flooding. When the city stopped maintaining alleys in the late 1980s, responsibility shifted to residents. However, with limited resources and a declining population, many of these alleys fell into disrepair, becoming symbols of urban decay. This neglect is further compounded by the increasing frequency and intensity of severe storms, which have exposed the city's vulnerabilities in stormwater management, leading to regular flooding.

To address these challenges, the "Alley Activation" project, launched in 2020 by a team of researchers at the UM-Dearborn in partnership with local residents and organizations, seeks to transform neglected alleys into vibrant greenways, rain gardens, and pollinator habitats. The project focuses on cleaning and greening alleys located in 2 neighborhoods namely Littlefield and McNichols. The activated alleys are bounded by Littlefield, Hartwell, McNichols and Outer Drive roads. These roads enclose an area of 141,436 square meters, located in the Bethune community and the Hubbell Puritan neighborhoods. Alley Activation involves clearing blocked alleyways and turning them into inviting, productive spaces that support sustainability goals. These revitalized alleys serve as a "green capillary system," contributing to the city's environmental, cultural, and social well-being. As these spaces are cleared, they offer a fresh opportunity to re-imagine their role and potential within the community. (1,2,3,4,5)

The Tbilisi Urban Forest is an ecological restoration project of 5,5 ha spanning two pilot areas initiated in 2020. Located on Mtatsminda ridge around Tbilisi, it is part of a larger reforestation effort within the 700-ha forest territory (Ref. 1,2). The project is funded by the Cartu Foundation and led by the Development and Environment Foundation along with Tbilisi City Hall. Restoration is undertaken to addresses significant challenges such as forest dieback caused by pest infestations, climate change adaptation as well as the creation of recreational infrastructure (Ref. 3,5). Through collaboration among interdisciplinary scientists and urban planners, a novel reforestation strategy has been developed that integrates patches of locally sourced plant communities tailored to diverse soil and slope conditions. This approach incorporates existing trees with new saplings, carefully grafted into existing soil pockets, and focuses on a biodiverse palette of endemic and climate-adapted species (Ref. 1,5). While the project implementation could not be carried out as planned, lacking public participartory due to Covid 19, still 100 jobs were created locally (Ref. 2). Ultimately, the Urban Forest project will enhance ecological connectivity, biodiversity and tourism and also serve the public as an improtant recreational site (Ref. 1,2).

The model farm is a small-scale organic vegetable farm according to the principle of a "market garden", meaning little machine use is required [1]. More than 40 different vegetables were grown in an effective growing area of 720 m2, using principles of regenerative agriculture promoting soil health [Ref. 4, 6]. An important outcome is sustainably producing vegetables for schools and care homes in the municipality [Ref. 1-3]. The initial vision was to "showcase both the farming and business model behind a sustainable and successful small-scale farming enterprise" and drive the "integration of regenerative farming practices in the continuous evolution of urban and rural multifunctional landscapes" [Ref. 4, 6]. The model farm offers education and cooperates with a local college [Ref. 1, 6]. The model farm is part of the Climate-KIC SATURN project which aims to reconnect urban and rural areas and address the climate crisis through sustainable food production [Ref. 1, 5, 7].

In the city of Cagliari, in the location of Mount Urpinu, 6400 new trees have been planted. The project, initiated in 2022, sought to restore the area's biodiversity and to revitalize the park for the benefits of the citizens (Refs. 1, 3 & 8). In fact, in previous years, the park has been subject to various environmental and social hazards because of its conditions: the area has been subject to wildfires and abandoned wastes, and with time, it became a gathering point for drug addicts and homeless people, thus becoming unsafe for citizens and especially for children (Refs. 1 & 6).
Therefore, the Metropolitan City of Cagliari decided to reclaim the area and plant thousands of trees of various species (holm oaks, oaks, pine, carob and olive trees) over more than 6 hectares of land (Refs. 3 & 8). The project's goal is to restore biodiversity, mitigate temperatures, decrease air pollution, and increase citizens' sense of community (Ref. 1).

Air pollution is one of the most pressing sustainability challenges in the UK, with particulate levels exceeding both WHO guidelines and EU safe limits in many cities (Ref 6). In 2014, Birmingham was identified by the WHO as one of nine UK cities breaching air pollution safety guidelines (Ref 2, 3).

In 2012, a soil-based green wall was installed at Birmingham New Street Train Station as part of a project aimed at improving air quality, as diesel train services contribute significantly to nitrogen oxide (NOx) pollution. However, most of the plants did not survive. In 2017, Network Rail commissioned a private company to reconstruct the wall using a hydroponic system (Ref 3). The new green wall was installed in 2018 and completed in May 2019 (Ref 1, 3).

This hydroponic green wall not only enhances the urban environment with calming green infrastructure, but also helps mitigate air pollution and promotes biodiversity with the addition of 16,600 plants (Ref 1, 2, 3).

The Rio Salado Habitat Restoration Area is a urban green space that transformed a former 5-mile-long city dump into a thriving riparian corridor (2, 3, 7, 9). The project, spearheaded by the City of Phoenix in collaboration with the U.S. Army Corps of Engineers, Maricopa County Flood Control District, and the Arizona Water Protection Fund, has revitalized a degraded ecosystem (9). Through decades of concerted effort, involving government agencies, non-profits such as the Arizona Sustainability Alliance, and community engagement, the area has been restored to a lush habitat supporting diverse wildlife, including over 200 bird species (1, 2, 7). The project aimed to mitigate the pressing issues of urban heat, air pollution, and habitat loss that Phoenix grappled with (1). By creating green spaces, improving air quality, and offering recreational opportunities, the Rio Salado Habitat Restoration Area stands as a testament to the power of collaborative conservation and community resilience (1, 6, 7, 9). The restoration area now boasts hiking and biking trails, a nature center, and various educational programs, making it a community space (3, 7, 9).