Lowered local temperature

The "Plan Arbre" is a tool for ecological planning and renaturation aiming to plant 308,000 trees between 2023 and 2029, sourced from the municipal nursery with seeds purchased from local suppliers (Ref 1, Ref 2). In 2023, 14,922 trees were planted, with plans to double this number in 2024 (Ref 1). The project addresses the loss of 50% of Marseille's natural spaces over the past 75 years, aiming to reverse this trend and reintroduce nature into the urban environment (Ref 2). It also tackles issues like drought and heatwaves, particularly in summer, by using trees and shrubs to cool the air, restore biodiversity, reduce air pollution, and enhance public spaces while absorbing CO2 (Ref 2).

The plan is divided into two phases. Phase I focuses on planting in Marseille's 58 parks and 273 squares and gardens, as well as around childcare centres, schools, socio-cultural centres, and sports facilities (Ref 2, Ref 3). From 2020 to 2023, various improvements were made, including playground renovations, installation of misting systems, automatic watering, and the creation of a CrossFit area (Ref 3). Phase II will involve identifying major boulevards, avenues, and streets lacking trees to enhance the urban canopy (Ref 2).
A diverse range of tree species were selected for their drought resistance, water efficiency, and ability to attract biodiversity (Ref 2, Ref 3). The project also focuses on increasing biodiversity and managing invasive species through natural methods to protect trees from pests without chemicals (Ref 3). Furthermore, the initiative includes de-impermeabilizing soils and implementing a smart irrigation system with tensiometric sensors, developed with the start-up GreenCityZen, which has saved 66% of water in two years (Ref 3). The Plan Arbre also promotes citizen participation, with 23 parks selected for community gardening projects, where ten winning associations will receive plants from the municipal nursery (Ref 1).

The city of Thessaloniki is tackling the energy crisis and climate change risks by prioritizing the installation of green roofs and green walls on school and municipal buildings as part of its resilience strategy, Thessaloniki 2030 (Ref 1, 2). One key project under this strategy has been implemented at EPAL Stavroupoli, one of the largest school complexes in the metropolitan area. The school, with a total built area of 11,918 sq.m and roof surfaces covering 6,042 sq.m, now includes a green roof covering 3,087 sq.m with 25,000 ground-cover plants, along with a vertical garden on three walls at the entrance, covering 100 sq.m and featuring 3,098 plants (ibid.).
The project is expected to yield multiple environmental benefits, such as reduced energy losses, improved thermal performance, enhanced sound insulation, better rainwater management, decreased runoff, and retention of harmful particles, all of which contribute to upgrading the area's green infrastructure (Ref 1). This initiative also strengthens the green fabric of western Thessaloniki and improves the local microclimate while addressing rainwater management issues (Ref 3, 4).

Minimizing heat stress is a critical priority for Phoenix, the hottest major city in the U.S., where heat-related deaths reached at least 359 across Maricopa County last year. The city's expansive urban layout and infrastructure exacerbate the urban heat island effect, making an already scorching climate even more hazardous. In addition, heat impacts communities unequally, with some neighborhoods up to 10 degrees hotter than others. Lower-income and predominantly Hispanic neighborhoods often have less canopy cover and fewer resources to combat rising temperatures, making them more vulnerable to extreme heat.
To address this, the City of Phoenix launched the Cool Corridors Program in 2020, a key initiative in its broader climate resilience strategy. This program, a partnership with American Forests and the Phoenix Street Transportation Department, aims to establish a network of shaded pathways that connect communities across the city. These corridors enable residents to travel safely to schools, public transit, and other city hubs, promoting environmental sustainability and public health.
The program prioritizes investment in low-income, heat-sensitive neighborhoods to improve tree equity and create green spaces where they’re most needed. The first Cool Corridor was developed in 2022 at Cesar Chavez Park, where over 250 trees were planted with the support of more than 100 volunteers, setting a strong example for future initiatives. By 2030, Phoenix plans to complete 100 Cool Corridors citywide, building a more resilient and livable urban environment for all residents. (1-5, 7-8, 10)

Over the past 10 years, Lima's population has grown from 8.2 to 9.6 million people. As the city's urban sprawl and population density have increased, green spaces have been replaced by grey infrastructure. Consequently, it has become challenging to ensure that residents enjoy a good quality of life (1, 2, 3). In December 2019, Lima City Hall launched "Limeños al Bicentenario," an initiative to revitalise the city's public spaces (1, 3). This program seeks to transform public areas through low-cost interventions, based on criteria such as vulnerability, citizen participation, and catalytic potential, among others (3). It also aims to foster social cohesion by involving residents in the maintenance of these newly renovated areas, while improving the city's resilience to climate change (1, 2, 3). Since its inception, the project has reclaimed 17 public spaces, covering an area of 41,000 m² (3). 430 trees have been planted, and the project has benefited from the collaboration of civil society and private sector partners (3). The programme also focuses on addressing climate change. Heat waves, droughts, floods and mass migration are the main climate-related risks affecting the city. In particular, the expansion of grey infrastructure at the expense of green spaces has exacerbated the risk of heat waves, causing temperatures to rise by up to 3.5 °C in certain areas of Lima (3).
One of the projects involved the recovery of public spaces in Teniente Pavia. For many years, the space was used as a public parking lot, and at night it accumulated garbage, there was alcohol consumption, drug use, and other problematic issues. There was no vegetation, benches or infrastructure for recreation. The neighbours, especially children, did not have access to green areas or recreational spaces (5). For this reason, in 2020 the project was initiated to repair sidewalks, plant vegetation, create gardens, and install infrastructure for play, rest, and exercise (3, 4).

Phoenix is one of the hottest cities in the United States, with temperatures regularly exceeding 40°C (104°F) for more than 90 days each year. The urban heat island effect is severe here, posing a significant health risk. Many communities in Phoenix lack equal access to shade cover—often, the impact of extreme heat disproportionately affects low-income neighborhoods that lack resources for tree planting and maintenance. In contrast, wealthier areas tend to have more trees and are visibly greener, which helps reduce the heat residents experience.
To address these disparities, the City of Phoenix partnered with SRP, a not-for-profit public power utility, to launch the "Right Tree, Right Place" program in 2018. This initiative aims to bring shade relief to areas most in need, such as parks, public transit stops, and schools, while replacing older trees that interfere with SRP power lines. SRP and the city work together to identify trees that pose risks to overhead power lines, and for each tree removed, three new trees are planted—either in a different location or with a species better suited to coexist with power lines.
One of the program’s notable projects took place in West Phoenix’s Cortez Park, where 24 drought-tolerant trees from four different species were planted. This diversity helps protect the trees against pests and other natural threats, ensuring their longevity and resilience. Through initiatives like these, the "Right Tree, Right Place" program contributes to Phoenix’s larger goal of developing a robust, biodiverse urban forest. By expanding green infrastructure, the city aims to reduce local temperatures, improve air quality, and create cooler, healthier neighborhoods for all residents. (1-8)

The Köprüköy Mosque in Adana, commonly named "green mosque", is one of a kind in Türkiye (Ref. 2,5). Its building and minaret are almost entirely covered by poison ivy and appear in vivid green colour from afar. Founded in 1929, it had to be remodelled in the early 60s as it couldn't sufficiently accommodate worshippers in the growing district. The mosque was then entirely built and rebuilt by the community, with its maintenance overseen by the mosque's protection association (Ref. 4). In the 70s, the ivy was planted and has since helped to protect the building from environmental stressors and keep visitors inside the garden and mosque cool during the summer heat (Ref. 4,5,6) Furthermore, the mosque’s well-maintained garden, home to around 280 species, is adored by local, national, and international visitors and tourists, as well as the media (Ref. 1,3,7). Frequent maintenance and rotation of the garden's flowers keep its appearance and function intact, one of which is the profound impact on visitors’ well-being, with many praising the unique atmosphere of the mosque that evokes peace, comfort, and spirituality (Ref. 1,3,4).
During COVID-19, the mosque could only host worshippers during praying hours, after which it quickly continued to bring people back together to garden, rest and socialize throughout the day (Ref. 1).

The Olive Garden ("Jardim das Oliveiras") is a green roof created in the Centro Cultural de Belém (CCB) in Lisbon, as a green space that blends natural elements with the surrounding cultural area and building. Situated by the Tagus River, the garden features a lawn, olive trees, and small lakes, offering a quiet place for people to relax and enjoy nature (Ref 1, Ref 2). It is a popular spot for families, young people, and children who use the space (Ref 1). The garden also hosts cultural events, such as concerts and DJ performances, adding to its appeal as a community gathering place (Ref 3, Ref 4).

San Borja has 1,347,000 square metres of green areas, equivalent to 12 square metres of green space per inhabitant, one of the highest ratios in the capital (1, 2). In total, there are 75 parks within its jurisdiction (1, 3). However, in recent years it has consolidated its role as a metropolitan urban centre and has become denser with new multi-family construction projects replacing traditional single-family homes with gardens (2). As a result, tree cover has decreased, affecting the creation of shaded areas and air quality, putting the health of residents at risk (2). Nevertheless, this municipality has reaffirmed its participation in the Global Covenant of Mayors for Climate and Energy, committing to implement policies and take measures to reduce (or limit where appropriate) greenhouse gas emissions and prepare for the impacts of climate change, as it is vulnerable to heat waves and droughts, as well as high wind and thunderstorm hazards and fires (1). Thus, since 2014, 56,000 trees have been planted, which is one tree for every two residents in the district (2). The mitigation programme includes 40 measures, including the creation and conservation of green areas, which involve planting trees to create urban forests to help regulate temperature, prevent heat waves, improve CO2 absorption, and preserve endemic species (1). In addition, the programme promotes the use of organic farming practices and the propagation of plants using natural methods (1).
One of the sectors where there has been the most progress is Sector 12, with 31% of the green areas created (3). Within this sector, the district is planting and creating an urban forest within the premises of the Army Headquarters, better known as ‘Pentagonito’. Its objective is to educate neighbours and promote greater environmental awareness (3, 4, 5).

The Green Wall of Tomesti was an initiative launched by the commune of Tomesti to combat air pollution from the nearby city of Iasi, which often drifted into the area (1, 2). The municipality decided to implement this solution after consulting specialists on how to address pollution from the main urban area. It was also integrated into the objectives of their 2014 General Urbanistic Plan, which aimed to transform Tomesti into a "modern, clean, and ecological area" (1, 2, 5). In addition to mitigating air pollution, the forest wall was expected to help lower local air temperatures (1).
The municipality purchased seedlings and planted the trees at the end of 2019, near the D.D. Patranascu school (1-3). While the overall goal was to protect the entire commune and improve the health of Tomesti's residents, particular attention was given to safeguarding the school closest to Iasi (1, 2). Before planting, the organizers called for volunteers to help with the plantation (3). In total, approximately 1,500 trees were planted (linden, acacia, oak and willow), with a space of 1,5 m between each other (2).
The action also follows on a 20-year national plan to increase forest walls to improve the quality of the air in the country (6).

Phoenix is grappling with severe urban heat problems. As the city continues to grow, it is expected to experience a rise in temperatures of three to five degrees on average in the coming years. This makes urban heat a significant concern, especially for vulnerable populations. Phoenix’s extensive urban sprawl, combined with a lack of green space, has exacerbated the urban heat island effect, where cities become significantly hotter than surrounding rural areas due to the high concentration of concrete, asphalt, and infrastructure. In 2022, Nick Lodato, the principal of Emerson Elementary School, wanted to mark the school's 100th anniversary in a meaningful way. He decided that planting trees would be the perfect way to celebrate this milestone while also benefiting the community. The tree planting event not only symbolized the school's strong sense of community but also represented an investment in its sustainable future. Prior to the project, Emerson had only 9% tree canopy cover, which was far below what is necessary to address some of the pressing environmental challenges Phoenix faces.
Tree cover has become critical infrastructure for heat mitigation. Trees provide natural shade and help cool the environment by reducing surface temperatures, which in turn lowers energy consumption and promotes better public health. In addition to offering shade, the native, drought-tolerant trees and plants planted at Emerson will also contribute to carbon sequestration, purify the air, and improve mental health by creating more green spaces for relaxation and outdoor activities.
To complete this project, Emerson Elementary partnered with the Arizona Sustainability Alliance (ASA), a local nonprofit. Together, they planted over 100 trees and plants across the school’s campus, with approximately 125 people attending the event. Volunteers included students and their parents, Tau Psi Omega fraternity members, APS employees, neighbors, former Emerson students and teachers. (1-3)