Wise viewers, welcome to Planet Earth: Our Loving Home for the first in our two-part series on green roofs or rooftops covered with vegetation to reduce the Urban Heat Island effect, promote energy savings, improve air quality, grow fresh produce, minimize storm water runoff and lessen climate change.

There are two main types of green roofs – intensive and extensive. The former requires a large flat surface area, features many kinds of plants including trees and shrubs, has greater than 10 centimeters of soil substrate and is high-maintenance. The latter has less than 10 centimeters of soil substrate, is generally made up of herbs, grasses, mosses and other types of groundcover and is low-maintenance.

Today we will focus on the greening of building rooftops in metropolitan areas. In large cities, skyscrapers, concrete buildings, infrastructure and pavement trap heat from the Sun, as well as waste heat from cars, air conditioning units, factories and other sources, creating “Urban Heat Islands” or UHIs. This effect can raise the temperature in a city two to 10 degrees Celsius higher than if it was a vegetation-filled rural area.

The United Nations Intergovernmental Panel on Climate Change states in its Third Assessment Report, “It is well-known that compared to non-urban areas urban heat islands raise [both] night-time temperatures [and] daytime temperatures.”

UHIs cause energy imbalances, degrade living conditions and can also affect local weather by altering wind patterns, producing clouds, fog and humidity and changing the frequency and intensity of precipitation. The extra heat generated by UHIs can induce thunderstorm activity. The resulting rapid, heavy rainfall heated by hot pavements and rooftops flows into streams, rivers, ponds, lakes, and seas producing stress in aquatic ecosystems.

In recent years, global warming has intensified and those living in large metros have been especially affected by rising temperatures exacerbated by the UHI phenomenon. In 2003 a devastating heat wave in Europe killed 35,000 people, many of whom were living in urban areas.

Many structures standing today are energy inefficient. For example, a 2007 analysis of China’s largest buildings, comprising 46 billion square meters of floor space found only four percent could be classified as energy efficient. Green roofs serve as extra layers of insulation, reducing the amount of heating needed in winter and air conditioning in summer, thus decreasing power consumption.

On a hot summer day, the rooftop of the City Hall building in Chicago, USA, a model intensive green roof, will be the same as that of the surrounding air temperature, say 32 degrees Celsius. By contrast, the rooftop of a neighboring building without any greenery may reach almost 71 degrees Celsius.

For many years Western European nations, particularly Germany, have been promoting the installation of green roofs to mitigate UHIs, improve local ecosystems and enhance the quality of city life. The green roof trend is now taking off in large Asian metros as well. For example in Japan, the government at the national and local levels has enacted laws to encourage urban roof greening.

We recently visited Tokyo and interviewed Mr. Taro Hitokoto, chief official of the Green Spaces Environment Office, a part of Japan’s Ministry of Land, Infrastructure, Transport and Tourism. Mr. Hitokoto will now discuss one of the Ministry’s demonstration rooftop garden projects.

This roof garden with an area of 500 square meters was installed on the building by the Ministry of Land, Infrastructure and Transport in 2002, seeking to verify rooftop gardening technology, measure the garden’s effects and provide information (on rooftop gardening) to the public.

Does it involve experimenting with weights of soil or which plants are suitable for rooftop greening?

Yes, when installing we seek weight-saving materials for greening and verify which of the various soils, pavements and containers are suitable. Also, we use environmentally-friendly materials such as scrap tires and paper for the pavement material.

Ten years ago when rooftop greening was not yet widespread in Japan, you started rooftop greening on the Ministry of Land, Infrastructure and Transport building. Could you tell us about the results of this project?

Yes. Actually, we have data showing that the inter-building temperature fell when the rooftop was greened.

How is it structured under this turf?

First of all, there’s a layer of light soil about 15 centimeters deep. Beneath this layer is a permeable filter, through which water can pass but plant roots cannot pass easily. Beneath it is a five centimeter-wide path for water to flow. At the bottom is a layer to protect the building from intrusion by both water and plant roots.

How many degrees did the surface temperature of the roof go down through the impact of rooftop gardening?

This graph shows the surface temperature during a day in summer, and here it is when the tiles become the hottest. Here is the surface temperature of the lawn. The temperature fell about 20 degrees Celsius.

I wonder how many beings have increased their presence due to this rooftop garden.

Up to now, 180 kinds of insects have been identified. The Imperial Palace is nearby and various insects fly in and live here since we’ve made a green space a little way from the Palace.

In Japan, local governments offer subsidies to popularize wall greening, or covering exterior walls of buildings with plants, and rooftop greening. We’ll next speak with Mr. Munetaka Takahashi about the operation of this subsidy system in Tokyo’s Minato Ward, as well as the current status of the program. Mr. Takahashi is the chief of the Greenery Promotion Subsection of the Environmental Section, a part of Minato’s Environment and Recycling Support Department.

Would you explain the subsidy system for rooftop and wall greening?

Minato Ward has been subsidizing those who install green rooftops since 2008; ¥25,000 (US$300) per square meter is the upper limit. The total subsidy amount is up to ¥5 million (US$60,000) and rooftop greening up to 200 square meters per building is subsidized. The actual result last year was 15 projects, which means an area of about 980 square meters of new green rooftop space was created.

Does the subsidy encompass all buildings including private residences and office buildings?

Those that have lot areas of less than 250 square meters are eligible. When a building of over 250 square meters is newly constructed, rooftop greening is required. Thus, we limit subsidies to buildings over five years old with lot areas of over 250 square meters. Our concept is to enable as many people to install green rooftops as possible.

I understand that in Minato Ward, the upper limit of the subsidy for rooftop greening was raised from ¥300,000 (US$3,500) to ¥5 million (US$60,000) in May 2008. What was the reason for this move?

Yes. Roads and buildings exceed 70% of the ward’s total area. As a way to increase green areas in this ward in the future, the rooftop space of a building becomes very important. In Minato Ward there is a lot of rooftop space on both private houses and office buildings.

We want to increase rooftop greening as much as possible, and in the case of private housing, it doesn’t cost much. However, promoting the greening of big buildings requires a lot of money. So, we think that large areas should also be eligible for subsidies. In Minato Ward, we are seeking a green ratio of 25% or covering 25% of the ward’s total area with plants. We are also about to promote rooftop gardening as part of a focused policy.

How effective was it to raise the upper limit of the subsidy? Has it contributed to increasing the area and the number of rooftop gardens?

After the upper limit was raised, we could secure five times the greened area of before.

How are you going to promote rooftop gardening in the future in order to reduce global warming?

We would like people to install green rooftops as much as possible, because it also becomes a measure to counter global warming. Also, we would like to continue with creating pleasant surroundings for living things and humans.

I think it’s really wonderful for the government of Japan to implement such a subsidy system for this highly necessary and effective approach to counteracting global warming. I sincerely hope other urban areas will be covered by green areas in the future. Thank you very much.

Thank you very much.

Finally we visit Meguro Ward Office’s green roof, which is very elegant. Our guide is Mr. Yojiro Shigeno of the Parks and Greenery Section of Meguro’s Urban Planning and Development Department.

What was the concept behind this roof garden, which is beautifully designed like a Japanese garden?

Yes, it’s a garden designed with a modern Japanese-style theme. It was designed by Dr. Kondo of the Tokyo University of Agriculture.

I saw a little while ago that the trees are watered by an automatic sprinkling system.

Yes, this automatic sprinkling system depends partly on wind power and solar-electric power generation.

Will you talk about future plans for rooftop gardening at the Meguro Ward Office?

Yes, the Meguro Ward is planning to build a rooftop park at the Ohashi junction in 2012. We will build a rooftop park on artificial ground about a hectare in size, where people will be able to enter. One building has already been built, but we’ll construct another one in the future to be connected by a bridge so that people can come and go freely.

The rooftop garden will slope and lead to the new nine-story building, and the park will slowly descend from the building’s ninth story towards the other building’s fifth story. Moreover, further ahead the park will be connected with Route 246 by a bridge, so that people can go down to a part which is as high as a two- or three-story building. This will be completed in 2012.

Thank you very much for speaking with us today.

Thank you for coming here.

We would like to sincerely thank Taro Hitokoto, Munetaka Takahashi, and Yojiro Shigeno for providing us with the opportunity to explore some of the cool and inviting green rooftops in Japan. May many more buildings in this great nation and elsewhere in the world soon feature their own gardens in the sky.

Friendly viewers, thank you for your company today on our program and please join us next Wednesday on Planet Earth: Our Loving Home for the conclusion of our series on green roofs. Enlightening Entertainment is up next, after Noteworthy News. May your days be filled with joy and love.