[Regular Series] Urban Greening and Disaster Prevention Part 2 ~The Era in which Greenery Protects Cities~

Rooftop and wall greening

Redevelopment and greening

"Square Turf KOZUIMUYO," a rooftop greening system that prevents rainwater runoff, installed on the roof

In 2025, heavy rain disasters continued across Japan. In Kumamoto Prefecture, record-breaking rainfall in August killed four people and damaged over 8,600 homes. In 2020, Kumamoto also experienced a major disaster caused by heavy rain, leaving 67 people dead or missing and 51 people with minor or serious injuries.^※[1]
In addition, typhoons have become noticeably larger in recent years, with some cases reported to have maximum wind speeds of 70 m/s, making this year a year that has once again made us realize the increasing severity of natural disasters.
Meanwhile, urban redevelopment is accelerating, and under the Urban Renaissance Special Measures Act, cities across the country are competing to build new towns. Large buildings are being constructed one after another, as if overcoming the threat of nature, and skyscrapers have become a common sight in major cities across the country.
However, when you look up at these skyscrapers from the ground, you will notice that many buildings have recently incorporated a lot of greenery. Toranomon Hills and Azabudai Hills have actively planted greenery on their walls and rooftops, and the adoption of greenery in buildings is increasing along with the spread of ESG investment and various environmental certifications.
Fukuoka City has a comprehensive subsidy system for greening, and many buildings in the city center are now equipped with green walls. Around Umekita Plaza in Osaka, large trees grow abundantly, and the lawns and architectural greenery between the buildings create a beautiful harmony. Furthermore, the introduction of greenery has progressed in the redevelopment areas from Shinagawa to Shimbashi, and it can be said that the effects and value of greenery in urban spaces are finally beginning to be widely recognized.

The dam effect of rooftop greenery

In this way, the effects of rooftop greening go beyond mitigating the heat island effect and improving the insulation performance of buildings; in redevelopment projects, they become the "face" of the city and an important factor in attracting people.
In addition, rooftop greening has a "dam effect" that temporarily stores rainwater and prevents inland flooding, making it an effective measure against urban flooding.
Kyodo KY-TEC's rainwater runoff control rooftop greening system, "Square Turf KOZUIMUYO," is capable of storing approximately 120 liters of rainwater per square meter. Products like this that also have the ability to control rainwater runoff are expected to play an increasingly important role in future redevelopment and urban development.
Furthermore, from the perspective of net-zero water buildings, if methods and systems for reusing rainwater that falls on a site or building not only for irrigating plants but also for toilet flushing and other utility water become more widespread, it will also lead to the revitalization of the greening industry as a whole.

The future of rooftop greening

In the future, rooftop greening systems that make effective use of rainwater will become mainstream, and traditional rooftop greening systems that constantly use tap water are expected to gradually be phased out.
The greenery around the ring at the Osaka-Kansai Expo created a wonderful landscape, but even though it was a limited-time event, it is undeniable that a considerable amount of water was used. From the perspective of us greenery experts, there were still issues in terms of sustainability.

Going forward, rooftop greening will require the early implementation of systems that minimize the burden on water resources, including groundwater, and that can irrigate plants using only rainwater.

Source:^※[1]Kumamoto PrefectureDamage information related to heavy rain from August 10th (as of January 9th, 2026)'

Writing/Responsibility
KYODO KY-TEC Co., Ltd. Environmental Business Department
Masayoshi Kawaguchi