Turning Gray to Green

Rooftop gardens create urban oases

By Yasushi Wada

Daily Yomiuri Photographer

Wandering around Tokyo's monotone concrete jungle in quest of a green oasis, I literally had to take to the skies to find what I was looking for. Lush greenery is more likely to be found on the rooftops of cutting-edge buildings, such as those in Roppongi Hills, rather than on street corners.

In recent years, rooftop gardening has received a great deal of attention as one way to tackle the so-called heat island phenomenon in which urban areas become significantly hotter than the suburbs.

In experiments conducted by the Construction and Transport Ministry, it was found that the surface temperature of the roofs of commercial buildings and condominiums exceeded 50 C in the daytime in summer. However, after trees and flowers are planted on the rooftops, the temperature drops to about 30 C, the ministry said.

The plants apparently help lower the temperature on the outer walls of the buildings, thus reducing the heat island phenomenon caused by heat absorption and dissipation. The increase in the number of rooftop gardens also is expected to help reduce carbon dioxide emissions.

In 2001, the Tokyo metropolitan government enacted an ordinance that required the owners of projected buildings over a certain height to include greening plans, such as rooftop gardens.

From the enactment of this ordinance until 2006, trees and flowers were planted on about 100 hectares of rooftops in Tokyo--a space roughly the same size as 150 soccer pitches. But the annual average pace of expansion of green rooftops is only about 20 hectares a year, making it difficult for the metropolitan government to achieve even 30 percent of its initial target of 1,200 hectares of rooftop gardens by 2015.

As a result, the metropolitan government last year announced a 10-year project aimed at greening 1,000 hectares in Tokyo by 2017 by planting trees and flowers not only on rooftops, but in parking lots and next to buildings. It also plans to cover schoolyards with turf and lay out new parks.

A bird's-eye view of Tokyo shows a mass of gray asphalt and concrete, with the exception of the few areas where a large park exists. If the metropolitan government succeeds in its greening efforts, how "cool" will the capital become in 2016, the year Tokyo hopes to host the Olympic Games?

Hopefully, it will be much cooler than this year. Weather forecasters are predicting that this summer will be hotter than normal. It is highly likely that a lot of people will be looking for a green spot in the shade this year.