Achieved increased protection against flooding

The Thalangama wetlands are part of a network of wetland ecosystems around Colombo city that spread over 20 km2 and provide critical life support to the city. These ecosystems keep people safe from floods, cool the air, filter polluted water, provide food and medicines, and fight climate change (10). These wetlands have become an environmental protection area and a biodiversity hotspot in a rapidly urbanising environment, as they host an array of plants and animals, including the endangered fishing cat and otter (5, 10). In 2007, Thalangama Lake and its surroundings were declared an Environmental Protection Area (EPA) under the National Environmental Act (4, 5). This protected area covers approximately 118 hectares (4) and includes two man-made reservoirs: Thalangama Tank (11 ha) and Averihena Tank (3.2 ha), located just 300 meters apart (5). The area hosts floating and rooted plants, scrublands, and trees that provide habitat to up to 100 species of migratory, resident, and endemic birds throughout the year. In addition, the area supports 30 species of dragonflies, 12 species of reptiles, 10 species of mammals, and 15 species of freshwater fish (1, 4). Since the lakes and their surroundings were declared an EPA, only limited uses are permitted, such as traditional fishing and rice cultivation (4, 5). The lakes are also important for floodwater retention and have high scenic and aesthetic value, attracting many visitors, and scientific and educational activities (5, 13).
However, due to the area's rapid urbanisation, land values have increased significantly, leading to excessive landfilling and the reclamation of paddy lands for housing. This is compounded by the indiscriminate disposal of garbage and construction waste and the spread of invasive species (5). These challenges have also led to the engagement of surrounding communities in managing and maintaining it (11).

Sri Lanka faces multiple natural hazards, including tropical storms, flash floods, and landslides. As the country's urban population has grown, development projects have encroached on wetlands, compromising their natural flood protection, air and water purification, and carbon storage capabilities. Additionally, hilly regions are at risk of landslides, particularly during the monsoon season, posing significant threats to vulnerable communities (4).
To address these challenges, the World Bank and the Sri Lankan government collaborated on the Metro Colombo Urban Development Project. This initiative focused on nature-based solutions (NBS) as cost-effective and sustainable approaches to risk management (4). By strengthening natural processes and ecosystem services, the project aimed to mitigate hazards such as floods, erosion, and landslides (4). Technical assessments by the World Bank highlighted the importance of wetlands in flood protection, leading to efforts to protect and restore 20 square kilometres of freshwater lakes, wetlands, and swamps (1, 4).
The project supported the Sri Lankan government in reducing flooding in the Colombo Water Basin and enhanced local authorities' capacity to manage infrastructure and services. It prioritised metropolitan investments to mitigate the physical and socioeconomic impacts of flooding and aimed to build long-term capacity for urban management and local service delivery (6).

To reduce the risk of urban flooding, the city of Seville, through its metropolitan water company Emasesa, established several "sustainable urban drainage systems". One of the pilot locations is on the Avenida de las Ascociaciones de Vecinos, where a rain garden complemented by an infiltration zone was established. The main aim of the project is to reduce the risk of flooding, but the system can also improve the urban landscape by offering green space, preventing desertification and reducing pollutants carried by runoff [Ref. 1-4]. After implementation, the project was shown to be effective during heavy rain [Ref. 5]. The system can store up to 34 m2 of water and reduce flow rates to the sewage network by 69 % and the total runoff to sewage by 93 % [Ref. 3-5]. The project was initiated and led by Emamesa, while two different companies were employed to design and construct the system [Ref. 1, 2, 6, 7]. The total budget of the project, which also included some renovations of grey infrastructure along the street, was 165000 EUR [Ref. 1].

Assemini, a municipality in Cagliari, has long grappled with hydrogeological instability, marked by major floods in 1999 and 2002. To mitigate future risks, the municipality launched a series of interventions focused on improving the hydraulic management of its waterways. These projects are part of a broader strategy to address recurring flood hazards exacerbated by the effects of rapid urbanization in the 1970s, which disrupted the natural water drainage systems (1,3). The central goal of the project is to reduce the risk of flooding by enhancing the functionality of existing waterways. This includes both preventative measures and structural improvements to the canal system to manage stormwater more effectively. These efforts aim to safeguard urban and rural areas from severe meteorological events. The project development involved a multi-phased approach starting in 2013, focusing on cleaning and maintaining minor waterways such as the Gutturu Lorenzu, Sa Nuxedda, and Giaccu Meloni streams. These efforts expanded over time, culminating in an agreement with the Land Reclamation Consortium of Southern Sardinia in 2015, securing both local and regional financial support. The interventions have covered over 24 kilometers of canals and streams, targeting key flood-prone areas (1,2).
Key interventions include the cleaning and maintenance of over 35 km of canals and streams, in partnership with the Land Reclamation Consortium of Southern Sardinia, supported by regional funding. A separate, large-scale intervention in Truncu Is Follas involves constructing an open-air diversion canal, a retention basin (44,500 m³), and new pipelines to redirect floodwaters, thus reducing risk for residents downstream in both Assemini and Elmas.

According to data from the National Institute for Space Research (Inpe), Rondônia ranks fourth nationally among the states with the highest number of detected fire outbreaks (2). In response to this issue and to restore devastated areas in the Amazon, Terra Cura was established in 2016 by resident Luana Lopes, promoting the planting of more than a thousand trees in the Porto Velho region (1). The areas benefiting from this initiative were those degraded by deforestation, causing erosion along the riverbanks (1).
This reforestation effort took place in the scenographic city of Jerusalem of the Amazon, from 2016 to 2022, a cultural and touristic complex in Porto Velho, where erosion caused by deforestation was observed along the riverbanks next to it (2). It was developed as a collaboration with the club and the founders of the Associação Clube Teatral Êxodo, who gave the space so that we could recover the land (3).
The project focused on developing an agricultural strategy known as syntropic farming, by implementing an agroforestry system. This approach seeks to reorganize and restore the natural environment, creating better conditions for planting and allowing trees to thrive. In the reforestation process, volunteers and experienced technicians worked together Additionally, the project included a nursery used for donating seedlings and for offering forestry and agro-construction courses to the community, held in the reforestation area (2).
The Terra Cura project, in addition to working on reforestation and recovery of degraded areas, promoted environmental and cultural integration at the site, promoting sustainable fairs and bazaars, training courses in ancestral practices such as soil cultivation and bioconstruction, and thematic events, bringing together artists and local communities (3). Although they were evicted from the area surrounding the scenic city of Jerusalem (5, 6), they are still active in the area.

Torslanda School is a newly built elementary school (years 0-6) where the schoolyard includes innovative ways to manage rainwater. The school was initially part of the Rain Gothenburg project, which aims to make the city, and this school, the best in the world when it rains. It was also a pilot project within the city's "equal building" initiative, aiming to make indoor and outdoor environments accessible and attractive to everyone regardless of gender identity, functional diversity or age [Ref. 1]. The main element of the schoolyard is a "river" to which water will be led when it rains, combining stormwater management with opportunities for play and education. The system will retain about 310 m3 of water and treat it before releasing it to a recipient. The river will be used to teach the children about climate, ecology, biodiversity and the water cycle. The river and schoolyard are connected to a natural wetland [Ref. 3, 4]. The school is run by the City of Gothenburg, who initiated the project, employing an architecture firm and a construction company to design and build the school and schoolyard [Ref. 3-5].

In an architecturally important area of Berlin, situated between the Landwehr Canal, the Kulturforum (the Berliner Philharmonie and the Berlin State Library) and the new construction on Potsdamer Platz, a combination of green and grey infrastructure has been realised to minimise the burden on Berlin’s existing water infrastructure.
Green and non-green roofs harvest annual rain, which flows through the site’s buildings and is used for toilet flushing, irrigation, and fire systems. The roofs retain and then release water to the large on-site buffer pond, which has five underground storage tanks. Next to the roofs, a series of urban ponds and connecting canals have been implemented, with a combined area of approximately 1.2 hectares. They are filled with rainwater, creating an oasis for urban life. Vegetated biotopes are integrated into the overland landscape and serve to filter and circulate the water that runs along streets and walkways. The lake’s water quality is excellent, forming a natural habitat for animals and cooling the surroundings, while fresh water usage in the buildings has been reduced. (Ref. 1; Ref. 2; Ref. 3; Ref. 6)
The project was implemented in the 1990s as part of the development of Potsdamer Platz in the wake of the reunification of Germany. Several architects collaborated on the implementation that was completely privately funded. Beyond its ecological and technical features, the site is a blue natural site in the heavily built city centre of Berlin and allows people to linger and enjoy natural features. The drainage system won several sustainability prices and is considered a successful integration of nature and technology-based mechanisms to foster climate change adaptation. As the rainwater system stores rainwater in underground tanks and ponds, the urban sewage system is relieved during heavy rain, and water can evaporate. Therefore, the small water circle is closed, and the microclimate is cooled. (Ref. 2; Ref. 6)

The ReDuna project, initiated in 2014, focuses on restoring the sand dune ecosystem in Costa da Caparica (Almada) in response to severe coastal erosion exacerbated by sea-level rise and winter storms. It aims to strengthen the resilience of dunes to environmental pressures while restoring ecological balance. Actions include sand nourishment, the installation of willow sand fences, and the planting of 100,000 native species. Community engagement was a key factor, involving local residents, NGOs, and schools in maintenance and replanting efforts. The project has been successful, with significant biodiversity recovery, establishing deep-rooted vegetation, and stabilising the dunes. Ongoing monitoring and adaptive management are central to its strategy, ensuring long-term sustainability. The ReDuna project serves as a replicable model for similar coastal protection initiatives globally (Ref 1).

D-Town Farm, located within Detroit’s River Rouge Park, is a landmark urban agriculture initiative led by the Detroit Black Community Food Security Network (DBCFSN). Since its establishment in 2008, this seven-acre farm—the largest in Detroit—has embodied the organization’s commitment to food sovereignty, justice, and security for the city’s African American community. Each year, the farm cultivates over 30 varieties of fruits, vegetables, and herbs using sustainable and regenerative practices. Key operations include large-scale composting, rainwater retention, solar energy generation, and beekeeping, all of which support its ecological and educational missions.
Beyond production, D-Town Farm serves as a community hub. From May through September, it hosts public events that offer educational and recreational opportunities for children and families. The farm also provides hands-on training for aspiring growers through internships and volunteer programs, fostering community engagement and agricultural skill development. Volunteers play a crucial role in daily operations, with ongoing opportunities available throughout the growing season.
D-Town Farm’s mission extends beyond agriculture, serving as a platform for broader advocacy. By challenging barriers to food access, it addresses food deserts with a focus on empowerment and education. The farm supports the local economy by supplying fresh produce to restaurants, farmers markets, and residents, while its health-focused initiatives, such as the youth-centered Food Warriors Development Program, aim to reduce health disparities within the community.
The DBCFSN’s work at D-Town Farm exemplifies a model of community cooperation and self-determination, promoting equity and justice in the food system. By engaging with both local and broader urban communities, D-Town Farm not only strengthens Detroit’s leadership in urban agriculture but also contributes to food justice movements nationwide.
(Ref.1,2,3,4)

Maskinparken is a new park covering 3700 m2 in the Lindholmen district, a new neighbourhood in a previous industrial/harbour area [Ref. 5]. The park is described as a well-needed green oasis or green lung in the developing area. The park finished construction in 2022 and is intended to provide access to green space for people living and working nearby. It is also designed as a blue-green stormwater management solution, where about 500 m3 of rainwater can be stored in the lower areas during heavy rainfall. Stormwater will be leaked from surrounding grey areas to the park to protect them from flooding. The Swedish National Board of Housing, Building and Planning (Boverket) has highlighted the park as a good example of climate adaptation in urban planning. The park has a variety of plants such as different tree species and flowering meadows, and plants that can withstand being soaked in the lower areas. Plants can grow in different landscape structures, such as hills and a pergola. The park also has amenities such as benches and lights, which are designed to mirror the style of the surrounding, older industrial brick buildings [Ref. 1-4].