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When green is good but land is scarce, plant rooftop gardens in the air

MANY apartment dwellers in Shanghai don't enjoy much of a view. They look out of their windows onto other apartment buildings and vistas of urban monotony. The only green they're likely to see is a small patch far below on the ground.

In Minhang District, however, a "three-dimensional gardening" project provides an eye-level sight for sore eyes and a place to rest weary bones.

The project covers rooftops with gardens that are mini-parks open to the public.

Those atop many buildings can be enjoyed by workers who take breaks sitting at tables under shade trees.

At different heights district-wide, gardeners are planting lawns, shrubbery, trees and flowers in the air.

There are birds, bees, butterflies and other insects and creatures flying, nesting, buzzing and crawling about. There may be beetles, worms and snails.

There are many kinds of sturdy shade trees and shrubs, including magnolia, box trees, "Buddhist pine" with red berries eaten by birds and sweet osmanthus.

The gardens are beautiful, fragrant and good for the environment, helping remove pollution from the air, cool the environment, insulate buildings and generally make urban living more pleasant.

They are good for people who live nearby and can visit them or simply appreciate them from their apartment windows.

Residents like 58-year-old Gong Yuemei now can look out a window and look upon the greenery.

Washing dishes and vegetables isn't such a chore when she can enjoy a view of the rooftop garden on a nearby primary school.

It's not the lush and fabled Hanging Gardens of Babylon, one of the seven wonders of the ancient world built by Nebuchadnezzar II around 600 BC - still, it's a further step in the city's greening process.

Last year, Minhang launched the project to put parks in the air, in a big way.

Around 100,000 square meters were covered with vegetation in 2008, and another 100,000 square meters will be completed this year.

Greenery on rooftops now represents more than 80 percent of the total greening project in the district - there isn't much land available for parks.

"Instead of dull and flat gray roofs, high-rise residents can now enjoy beautiful green sights when looking through the window," says Mao Qinying of the Minhang Greening Management Bureau. He's in charge of the three-dimensional greening project.

The importance of green space in urban planning has been widely accepted, especially green space near residential areas. But finding places for greenery in densely populated urban centers is difficult as little land is available.

The idea of three-dimensional greening, especially green roofs, started first in Europe and then spread to other areas, says Li Jingshen, professor of urban planning at Tongji University.

Rooftop greenery, and sometimes usable gardens, came to Shanghai around seven years ago.

In Minhang, rooftop gardens were first placed on government buildings, schools, hospitals and private enterprises, like shopping malls.

The district government paid for all district-level airy parks; it paid for half of the town-level public gardens and 30 percent of the gardens atop private buildings in 2008.

This year the district will pay half the cost of rooftop gardens on private buildings.

Greening official Mao says the success of the rooftop gardens so far has demonstrated their feasibility and many schools, hospitals and shopping malls have applied for funding. This year new residential communities will be covered.

"Rooftop green space gives great benefit for little investment," says Mao.

It only costs 125 yuan (US$18.30) per square meter for a rooftop lawn and 370 yuan per square meter for a rooftop garden.

Planting rooftop gardens combats the urban "heat island" effect.

Traditional building materials soak up the sun's radiation and re-emit it as heat, making cities at least 4 degrees Celsius hotter than surrounding green and rural areas.

A green garden "cloth" covering a bare roof reduces heat absorption and re-emission.

It also improves building insulation.

A study by Environment Canada found that a green roof results in a 26-percent reduction in summer cooling needs for air conditioning and a 26-percent reduction in winter heat losses.

Minhang research showed that indoor temperatures of a building with a green roof are 3-5 degrees Celsius lower than those of a building with an exposed roof.

This means less greenhouse gas is discharged and there's reduced need for air conditioning. A small way to fight global warming.

Extensive use of green roofs also help with storm-water runoff management.

Heavy storms can overload the wastewater system and cause flooding, dumping raw sewage into the local waterways.

Green roofs can reduce the amount of runoff from the roof.

Studies show that roofs can retain up to 75 percent of the rain water, gradually releasing it back into the atmosphere through condensation and transpiration, while retaining pollutants in their soil.

Green roofs also can provide habitats for insects and birds. Even gardens 19 stories high can attract birds, bees and butterflies.

Clearly, gardens are heavy and not every roof is suitable for retrofitting and special water proofing.

As the soil is not very deep, roof gardens require vegetation with spreading transverse roots, not deep roots.

Trees and vegetation need to be sturdy and capable of withstanding wind.

Yulan magnolia, sweet osmanthus, small conifers and box trees are widely used in Minhang.

Early roof gardens

The earliest elevated gardens can be traced back to 2000 BC in Ur in the lower reaches of the Euphrates River (today's Iraq).

Traces of vegetation were found on the third level of a ziggurat (terraced pyramid), not on the top.

The first real roof garden appeared in Babylon in about 600 BC, the famed Hanging Gardens of Babylon, or the Hanging Gardens of Semiramis, one of the original seven wonders of the ancient world. The site is near present-day Al Hillah, Babil, in Iraq.

The gardens, on multiple levels, were as high as 23 meters. They were built by Nebuchadnezzar II to please his ailing wife who longed for the fragrant trees and plants of her native Persia.

The gardens were destroyed by several earthquakes after the 2nd century BC.

Roof gardens in China

The first basic roof gardens appeared in China in the 1960s. Vegetable and fruit gardens were planted on the roofs of factories, offices and office buildings in Chengdu, capital city of Sichuan Province, and Chongqing.

The first proper rooftop garden was built on the roof of the Guangzhou Dongfang Hotel in Guangdong Province in the 1970s. The first big outdoor roof garden was built in 1983 on the roof of the Great Wall Hotel in Beijing.


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