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A Green Roof Strategy for Beijing

April 16, 2013
green roofs in wangjing

Existing green roofs in Wangjing

Beijing air pollution continues to be a mainstay in conversations here in Beijing. International and Chinese friends often ask me how long it will take to reduce Beijing’s air pollution down to a reasonable level.

“A very long time,” I reply.

As I’ve stated before, Beijing is geographically situated in a basin that traps air pollution above the city. Air pollution, though, is not the city’s only environmental challenge. Beijing will continue to be confronted with a laundry list of environmental challenges, successfully confronting these challenges will require a diverse toolkit. One of these tools, as Gavin Lohry argues in a recent study on the value of green roofs in Beijing, may be green roofs.

Gavin’s report is an extended argument for the increased adoption of green roofs to mitigate environmental challenges in Beijing. This study is composed of two primary sections–benefits of green roofs and a calculation of their applicability in Beijing. Gavin first lauds the environmental benefits of green roofs: they reduce energy demand in both the summer and winter; they reduce storm water runoff; they reduce of air pollution; and they mitigate the urban heat island effect. Green roofs were initially developed for their insulation benefits, and this is generally considered their most valuable attribute. One study records heat gain reduction levels of green roofs at 70-90% in the summer and heat loss reductions of 10-30% in the winter. These numbers vary with the quality of insulation. Green roofs directly reduce air pollution by absorbing particulate matter, Nitrogen Oxides (NOx), Sulfur Dioxide (SO2), and Ground Level Ozone (O3).

extrapolation

Extrapolation of the amount of potential green roofs in Beijing

Gavin’s environmental benefit assessment process

Gavin’s environmental benefit assessment process

The second part of Gavin’s study is the calculation of the feasibility of widespread of adoption of green roofs in Beijing. Gavin selected the Northeast Beijing neighborhood of Wangjing (望京) to extrapolate the value of the environmental benefits of a widespread green roof program to the city of Beijing. He maps out Wangjing roofs, examines each roof’s suitability as a green roof, and extrapolates this data across the entire city of Beijing to determine the potential benefit of widespread adoption of green roofs. His air pollution figures are below. Gavin summarized the environmental benefits of a widespread, 29 billion yuan (US$4.7 billion), green roof program in Beijing in a recent opinion piece.

Under this scenario, air particle pollution could be reduced by as much as 880,000 kilograms every year, equivalent to taking 730,000 cars off the road. The roofs could reduce storm water by 3.5 million cubic metres during large rain events, equivalent to filling the Forbidden City and Tiananmen Square with two metres of water or 1,400 Olympic swimming pools.

In addition the average summer temperature in Beijing would be reduced by 0.32°C, with greater reductions during peak hours. Finally over half of the green roof area would see a significant increase in insulation leading to lower energy use for heating and cooling.

Block ACG DescriptionA chart detailing Gavin’s findings and how they are applied across Beijing is below. NRDC’s Sustainable Cities team works with the Chinese Ministry of Housing and Urban-Rural Development (MOHURD) to encourage urban development policies that lower energy demand, reduce urban air pollution, and mitigate climate change.

Area Name
Roof Area 

Meters2
Neighbor Area Size
Green Roof Cover %
Air Pollution Removal kg
A-Block
27,884
269,825
10.3%
238kg
C-Block
31,211
282,126
11.1%
264kg
G-Block
25,874
220,012
11.8%
222kg
A-Green Roof Area
3,393
269,825
1.2%
30kg
A-Block Combine
31,277
269,825
11.6%
268kg
Wangjing Area
683,941
10,795,000
6.3%
6,413kg
Beijing Area
93,258,522
1,480,294,000
6.3%
879,400kg
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One Comment leave one →
  1. June 2, 2013 05:25

    Reblogged this on Jugraphia Slate.

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