Achieved improved stormwater management

In 2012, PRZHT (Pôles Relais Zones Humides Tropicales) initiated Project REMA, an effort dedicated to the conservation and rehabilitation of ponds in the Antilles, with backing from the IUCN. Wetland ecosystems in Martinique and the Caribbean had long been overlooked. However, interest in these habitats grew after PRZHT introduced an interactive virtual tour of Antilles ponds in 2019. Project REMA emerged in response to local concerns about the lack of technical resources for pond restoration in the French West Indies. While similar initiatives had been undertaken in France, there was no specific guide tailored to this region. Though originally conceived in 2012, the project remained dormant for several years before fully launching in 2019. Between 2019 and 2021, restoration experiments were conducted on 12 ponds across Martinique, Guadeloupe, and Saint-Martin, laying the groundwork for a comprehensive technical manual.
Building on this success, REMA II was introduced in January 2024 with a three-year scope. This new phase will focus on restoring and maintaining 80 ponds, both public and private, in Martinique and Guadeloupe. Additionally, it will address the management of invasive species and incorporate eDNA analysis to enhance conservation efforts. These small wetlands play a fundamental role in flood regulation, water storage, pollutant filtration, erosion control, and carbon absorption. They also provide refuges for biodiversity and contribute to the resilience of territories in the face of climate change.
(1, 2, 3)

HortaFCUL is a project created and managed by the Faculty of Sciences at the University of Lisbon to raise awareness and promote the practice of permaculture as a solution to the ecological, social, and economic problems the world is facing (1). This initiative began in 2009 on the University campus through a garden, which allowed HortaFCUL to start conducting some activities that could answer some socio-environmental challenges, such as food security and sovereignty, ecosystem degradation and climate change (13), by raising awareness, teaching, and practising many aspects involved in permaculture and urban agriculture (2). Its focus has been on regenerating soil in an urban environment and creating productive landscapes for people and other beings (12). They grow different types of plants (vegetables, shrubs, trees) in different ways (swales, raised beds, greenhouses) to increase plant diversity and foster ecosystems (13).
The project is managed by students and researchers, who hold educational activities, such as courses, workshops, and dissemination activities (events, discussions, fairs, and conferences) (2). The project is organised according to a non-hierarchical sociocratic model, in which all decisions are made as a group, and where all ideas, critiques, and suggestions are seen as added value and an opportunity to improve techniques and knowledge (3). Additionally, it is open to the community, allowing anyone interested to participate and volunteer (1).
HortaFCUL is also one of the pioneering permaculture projects in operation in the Lisbon region and is now recognized as a national reference centre for permaculture (2). Since its inception, HortaFCUL has sought to be a hub that attracts people, organizations, and other initiatives, and it is currently a point of contact between different projects and associations, such as local businesses, educational institutions, and networks (5).

In 2018, the City of Detroit implemented a drainage charge to help cover the costs of capturing, conveying, pumping, treating, and safely returning combined sewage to the Detroit and Rouge Rivers (1). The charge is calculated based on each parcel’s impact on the sewer system, particularly by measuring impervious acreage (1). Since then, this fee has posed significant challenges for one group in particular: Detroit’s houses of worship (2). Churches, with their large roofs and parking lots, face higher monthly drainage charges, creating financial strain for many faith leaders (2).
To support these institutions, Sacred Grounds has been providing grants, labor, and design assistance to install projects that reduce water bills and drainage fees (2). Sacred Grounds collaborates with the National Wildlife Federation, Friends of the Rouge, and Sierra Club of Michigan to implement these projects through the city’s green credit program (2). A recent initiative involved installing four rain gardens located on the perimeter of St. Suzanne Our Lady Gate of Heaven Church (3). These bioretention gardens, funded by several private and public actors and led by Detroit Future City, diverts water from 20 large downspouts, redirecting an estimated 500,000 gallons of runoff annually away from the municipal sewer system (3, 4).
In addition to managing water, the gardens foster a thriving habitat for pollinators and adds beauty to the area (3). St. Suzanne’s commitment to environmental education includes engaging over 130 youth and adults in training programs that build pathways to STEAM careers and opportunities where local residents are often underrepresented (4). The church also features an innovative, eco-friendly outdoor classroom developed by students, further supporting their sustainability mission (4).

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.

Arizona is experiencing an unprecedented drought, now nearing 15 years and surpassing the most severe drought in over 110 years of recorded history (1). For Phoenix residents, accustomed to extreme heat and minimal rainfall, rising temperatures are bringing new health risks (3). Diminished rainfall not only leads to water scarcity but also raises temperatures, as the sun’s energy, instead of being absorbed to evaporate moisture, intensifies the heat on the ground (2). In 2023 alone, extreme heat claimed at least 147 lives, with Arizona seeing the majority of these fatalities. By early August, over 100 heat-related deaths had been reported in the state (2).
In response to these challenges, the Watershed Management Group (WMG) has collaborated with Arizona State University’s Sustainability Teachers’ Academies to develop a program that maximizes the desert’s limited rainfall to build community resilience (3). Their Schoolyard Water Education Program brings educational services to Phoenix schools, focusing on designing and installing rain gardens as part of outdoor learning initiatives (3). This hands-on approach transforms schoolyards into interactive laboratories where students learn the principles of sustainability through direct engagement with their surroundings (3).
A project at Clarendon Elementary School in Phoenix involved constructing a rain garden with native plants and wood chip mulch to help retain moisture (3). These gardens offer students a living classroom, where they can observe seasonal changes in native plant life, distinguish beneficial species from invasive weeds, and track rainfall to measure the garden’s water intake from rooftops and direct rain (3). Beyond the academic learning, rain gardens provide cooler, safer spaces for students to gather, fostering a lasting connection with nature and a deeper understanding of sustainable water practices (3).

The schoolyard at Reginhard Primary School in Reinickendorf faced persistent challenges, often becoming unusable due to poor drainage. After rainfall, water would pool, leaving the yard submerged and inaccessible to the 400 primary school pupils. Even in dry weather, the schoolyard was far from ideal: a lack of play equipment made it uninviting, and in summer, the area became excessively hot, offering little comfort or shade. Both children and the school community, including teaching staff and parents, voiced a strong desire for improvement.
Adding to the urgency for redesign, Berliner Wasserbetriebe imposed a discharge restriction, requiring rainwater to be managed on-site. This led to a comprehensive transformation of the school grounds. Large areas were unsealed, allowing water to seep naturally into the ground. Underground seepage systems were installed to enhance drainage, and the redesign introduced green spaces, a school garden, and near-natural play and exercise areas. These changes not only resolved the flooding issue but also created a more inviting and sustainable environment for students.
The focus on ecological and sustainable design improved the microclimate, providing cooler surroundings and enabling outdoor breaks filled with activity and fresh air. The redesign transformed the schoolyard into a vibrant space that meets the needs of both children and the environment.
This project was funded by the Berlin Programme for Sustainable Development (BENE Umwelt) and financed by the European Regional Development Fund (ERDF). (Ref. 3; Ref. 4)

On a small roadside green space in Berlin, a tiny forest was created. The idea of Tiny Forests comes from Japan, there are already some in France and the Netherlands, and since 2020 also in Germany. Tiny forests are constituted of trees planted densely next to each other in small spaces, such as tiny green roadsides.
At Oderstraße, the NGO TinyForestBerlin planted an even smaller forest, a nano forest on a roadside where trees cool down the area, filter the air and create a habitat for insects. Trees in urban areas loosen up the dense and degraded soil, allowing it to store carbon and let rainwater properly seep into the ground to prevent urban flooding. Roadsides are hardly utilised or recognized in their environmental potential, such as hosting a nano forest. Projects like the one implemented by TinyForestBerlin present an approach for collaboration between the district and civil society, as the district's park department lack the capacity to maintain small roadsides. The project at Oderstraße is the first official tiny forest in Berlin, as a previous planting campaign in Friedrichshain was not entirely legal due to missing approval of local authorities. (Ref. 2; Ref. 5)
The TinyForestBerlin association has set itself the goal of creating such small nano-forests all over Berlin. An ambitious project that aims to enrich the city's green spaces and contribute to improving the urban climate. The trees planted on Oderstraße are one of many smaller planting projects that are spread throughout the city on public as well as private land. (Ref. 3)

On the site of a former malthouse in Berlin, a company has developed a sustainable rainwater storage system to prevent flooding in the sealed environment, which had been vacant for several years. Once used for malt production, the site is now home to offices, studios, manufacturing businesses, and hosts sustainable events. The site's transformation includes natural gardens, tenant gardening beds, green roofs, and two outdoor water basins that retain rainwater, creating a blue space for recreation. (Ref. 1)
The two ponds are filled with filtered rainwater, and an underground tank stores additional water, allowing it to seep away gradually. Native plants surround the ponds, creating a habitat for local wildlife. Given that much of the surrounding area is sealed, the ponds help mitigate urban flooding by managing and storing rainwater, reducing the site's reliance on the urban sewage system. Additionally, as Berlin faces extreme heat in summer, the project offers a cooling effect and provides access to filtered water during droughts. (Ref. 1; Ref. 2)
The project is managed and financed by IGG Malzfabrik mbH, which oversees the entire site in Berlin's industrial area and rents out office spaces to various companies. This initiative is part of a broader sustainability strategy that addresses social, economic, and ecological factors, and it is featured in the company’s common good economy report (Gemeinwohl-Ökonomie Bericht). (Ref. 5)

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].