Adding greenery to the rooftops in a city can help fight climate change.
Credit: iStockphoto
SYDNEY: Replacing traditional roofs with gardens could help fight climate change, by acting as a carbon sink and cooling cities, say U.S. scientists.
If all rooftops in an urban area with a population of about one million (roughly the size of Adelaide or Detroit), grew these rooftop gardens, it would be equivalent to eliminating a year’s worth of carbon dioxide emitted by 10,000 large cars and trucks, say the scientists, based in Michigan.
“Widespread use of [rooftop gardens] would definitely be improving our management of carbon, especially in large cities where rooftops cover a great deal of land area,” said researcher Kristin Getter, a horticulturist at Michigan State University, in East Lansing, whose study was published in the journal Environmental Science & Technology.
Roofs could become carbon sinks
The soil depth and plant types used in rooftop gardens varies, and some can even support trees, however due to building weight restrictions and costs the gardens usually have a shallow layer of soil and small succulent plants.
This strategy to combat global warming draws on the natural process of photosynthesis in plants, which removes carbon dioxide from the atmosphere and stores the carbon in plant biomass and soil. Utilising the space on empty roofs to grow plants has the potential to be an effective carbon sink.
Two experiments were conducted during study. The first experiment involved eight green roofs in Michigan and four in Maryland, ranging from one to six years in age. All 12 roofs were composed primarily of Sedum species (hardy and low growing, shrubby plants) and had soil depths from 2.5 to 12.7 cm.
The second experiment installed an extensive green roof on the Plant and Soil Sciences Building on the campus of Michigan State University. The green roof consisted of six centimetres of soil and four of the most commonly used plants in green roofs in the region.
375 g of carbon per square metre
Plant and soil samples were randomly harvested every month during the growing season for two years. These harvested samples were then analysed for the amount of carbon they contained.
On average, each green roof system had the capacity to sequester 375 g of carbon per square metre of roof.
In addition to absorbing carbon from the environment, Getter said green roofs offer other benefits such as improving stormwater management, conserving energy, air and noise pollution mitigation, and increasing urban biodiversity.
“These results may [also] allow building owners with green roofs to trade in carbon-based commodities,” said Getter, who is currently studying the effectiveness of growing fruits and vegetables on green roofs as a means of growing local produce in dense urban populations
I love this idea! As well as
I love this idea! As well as all the environmental benefits, I think it will do a great job of making less cities more alive, less concrete jungles.
Roofgardens' carbon footprint
What is the carbon footprint of electrically pumping 90 litres of water up to the 80th floor of an office block to water the garden? One bucket of water contains 9 litres, so 90 litres is 10 buckets of water a day which seems about right to water a rooftop garden exposed to high winds and high temperatures. How would this affect the "carbon savings" equation? Aren't we being encouraged to save water and electricity?
Tollgates
Little or no water
Little or no water would be necessary for the green roofs mentioned in the article because the plants studied are plants that are adapted to living in places that are hot & dry, arid conditions like deserts. They have thick, fleshy leaves that can retain water over very long periods of time.
All 12 roofs were composed primarily of Sedum species (hardy and low growing, shrubby plants
reply
surley offices have so many employes that they can find someone in the day to go up and water the garden by hand. there is no reason that they have to electrically pump the water.whats wrong with good old fashioned labour?
Where do the solar cells go?
I thought these buildings were supposed to use all that idle roof space to generate power through solar cells and or windmills. Now someone is suggesting we revert to the idea of roof top gardens. I know which I would rather look at and be amongst and it is not the power infrastructure...
I Hate Nay Sayer's
How come when someone comes up with an idea that works on a small scale test, some people say "it will never work"? Apparently it does or they wouldn't be on this page. I have a small garden and not just to keep food costs down. Not only is it cathartic but I feel it does help and I'm not a big tree hugger either.
Thank you!
roof top gardens
Some thoughts from a backyard greenie:
Garage roofs are great in melbourne to grow pumpkins.
Trouble is that you need a harness pole to safely tend the plants.
Retro fitting a roof may impact on heightlimits and shading of neighbouring homes and outdoor spaces epecially if the plants are not deciduous. It probably needs to be designed into a new estate. Current community vegegardens could move up onto council rooves but public liability issues will stifle that.
Rooves can get very hot so a lot of water would be lost to evaporation.
HYdroponics is probably the go.
Veges may be more contaminated with pollution.
Green walls ar also an option.
Hey we will be going back, er.. forward to a form of 21st century cave dwelling.
If it happens I would like to see native plants to attract the native birds.
If it adds half a kilo in two years per square meter we would need to harvest it to reduce the weight load on the rafters then what do we do with the carbon material if it is not edible?
regards
Lisa an apprentice greenie.