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The Setagaya Trust & Community Design was established in 2006 through the merger of the Setagaya City Urban Development Corporation (founded in 1980) and the Setagaya Trust Association (founded in 1989). The organization supports resident-led community development, working closely with local citizens who want to improve their neighborhoods and helping to build a Setagaya where people, city, and nature coexist.
Kakuya explains, "Setagaya has developed as a residential city, but its residents remain deeply committed to preserving greenery. Our role is to help give shape to that commitment."
The Setagaya Trust & Community Design currently operates with a staff of 60 and is supported by roughly 500 volunteers, about 2,000 members, and private-sector partners.
The organization works to address local challenges—managing privately owned woodlands and green spaces, repurposing vacant houses for community benefit, and supporting open garden programs—while helping to create communities that encourage interaction among residents.
The organization had long been involved in activities that support green infrastructure, such as conserving green spaces, but in fiscal 2020, it launched a new initiative: "Rain Gardens You Can Create."
A rain garden collects rainwater from roofs and paved surfaces, holds it temporarily, and allows it to gradually soak into the ground. This helps reduce urban flooding and ease the heat island effect, among other benefits. Rainwater stored in tanks can also be used for watering gardens or during emergencies.
Kakuya said Setagaya has many single-family homes, and that the rain garden initiative grew out of the idea that if each household created one, it could help reduce flood risk across the community.
Staying true to the idea that anyone can create a garden, the initiative focuses on making rain gardens easy to build and enjoyable as an extension of everyday gardening, using materials readily available at home improvement stores. Planting a variety of species also helps create habitats for local wildlife.
Kakuya says, "Instead of leading with flood control, we aim to engage people by highlighting the pleasure of growing plants and the beauty of creating a well-designed garden."
Launched in fiscal 2021 and organized by Setagaya City, the Setagaya Green Infrastructure School offers a three-session course led by specialists. Participants learn the fundamentals of green infrastructure, including the role of rainwater and plants, while gaining hands-on experience building rain gardens. Now in its fifth year as of fiscal 2025, the program remains highly popular, attracting large numbers of applicants each time. To date, around 100 participants have completed the course after being selected by lottery. In response to graduates who expressed a desire to stay involved in the ongoing care of rain gardens and plants, a monthly initiative known as the "Okusawa Community Rain Garden" has also continued. As part of this effort, participants gather once a month to maintain the rain garden and surrounding vegetation at Okusawa Nichome Park.
The organization has also published a booklet titled A Guide to Creating Your Own Rain Garden for those interested in giving it a try. Volume 1 is a practical guide that explains the materials needed and the steps involved in creating a rain garden of about 3.3 square meters. Volume 2 introduces 5 real-world examples of rain gardens built at private homes and other sites. The guide is available at Setagaya Trust & Community Design's offices and visitor center, and can also be downloaded from the organization's website.
The Trust Midori Section has set up a dedicated help desk for rain garden projects and, when needed, can also arrange support from partner architects and gardeners.
Kakuya says that architects handle the planning, taking into account environmental conditions, the structure of the home, and how rainwater flows, while gardeners are responsible for selecting plants and designing gardens suited to each site. She adds that because every consultation is different, responding properly often requires time and careful attention.
Supporting rain garden projects requires tailored, cross-disciplinary expertise, making intermediary support organizations such as Setagaya Trust & Community Design increasingly important.
In 2024, the Tokyo Metropolitan Government launched the Rainwater Infiltration Project as part of a broader effort to reduce urban flooding by encouraging city planning that limits rainwater runoff. Setagaya Trust & Community Design has been designated a "Rainwater Infiltration Ambassador" and, through its active initiatives, is helping promote wider adoption of rainwater infiltration-focused community development.
In December 2024, efforts to promote rain gardens as a form of Nature-based Solutions (NbS) were recognized with the Minister's Award at the fifth Green Infrastructure Awards, hosted by Japan's Ministry of Land, Infrastructure, Transport and Tourism. The award was received jointly with the nonprofit organization Rainwater Community Development Support.
Kakuya says that the award has sparked an increase in study visits, especially from those interested in green infrastructure and the "Rain Gardens You Can Create" initiative. She adds that inquiries have been coming from a wide range of sources, including national and local governments as well as private companies.
Among organizations working on green infrastructure, Setagaya Trust & Community Design has attracted particular attention for the way it expands its activities by respecting residents' initiative and emphasizing human resource development.
The rain garden initiative has also drawn growing interest from the private sector. To date, the organization has received donations from Mitsui Sumitomo Insurance and has carried out rain garden projects as part of employee training programs for Cainz, a home improvement store operator. As companies increasingly engage in efforts to protect, restore, and regenerate nature, Setagaya Trust & Community Design sees strong potential to further expand the reach of rain gardens through partnerships with the corporate sector.
What began in Setagaya as a small, resident-led effort to build rain gardens has evolved into a new model for community development—one that supports coexistence between cities and nature by bringing together residents' commitment and professional expertise.
By maintaining green spaces with healthy, permeable soil and encouraging interaction among residents through these activities, the initiative "helps strengthen a city's disaster resilience," Kakuya says.
Kakuya explains, "Green infrastructure and rain gardens are, at their core, just one tool for community development. What really matters is creating opportunities for people to connect and places where they feel at home, and keeping those relationships alive day to day—that's the role of a local community."
As climate change increases the risk of urban flooding around the world, expanding bottom-up environmental efforts that begin with small, individually built rain gardens—alongside government-led infrastructure—can help strengthen disaster resilience across communities in high-density cities like Tokyo. In doing so, they offer a sustainable model for urban green infrastructure.
Rather than pushing communities toward solutions from the top down, the aim is to cultivate approaches that encourage each individual to think, "I'll give it a try." This is how environmental coexistence and community cohesion can be realized together, helping to sustain community development over time.
Operating on the concept that envisions green urban development for the next 100 years, the Tokyo Metropolitan Government is pushing initiatives to protect, cultivate, and utilize Tokyo's greenery.Through the efforts of both individual citizens and various entities, the aim is to transform Tokyo into a sustainable city that exists in harmony with nature.TOKYO GREEN BIZ - Green Urban Development -TMG
