Abby Schultz's Blog

Abby Schultz is a writer and consultant who looks at how companies grapple with climate change and dwindling natural resources in a global culture that expects, even demands, constant growth. Abby has written about the intersection of business and the environment from the U.S., and is fascinated to learn how companies in Asia’s fast-growing economies are confronting – or not confronting – environmental issues fundamental to their operations. She’s also interested in how innovative businesses come up with creative solutions for operating in a resource-constrained world. Abby has written about corporate social responsibility, clean tech investing and socially responsible investing, among other environmental topics. She’s also written about markets and personal finance, for major news organizations including CNBC.com, Dow Jones and The New York Times.

Greening Hong Kong

Getting Plants to Grow on Rooftops Without Much Water
March 25, 2013

Planting vegetation on city rooftops can have a huge effect on the environment as plants cool the atmosphere and absorb heat as well as filter carbon dioxide and other pollutants. Green roofs also absorb excess rainwater and reduce the need for heating and cooling.
 
But during Hong Kong’s dry season, from October through March, green roofs require watering, and while most of us don’t like to think about it, water is a scarce resource, particularly in China where water usage is on a path to outstrip supply.
 
One purpose of this blog is to highlight businesses with intriguing innovations that are making the transition to a sustainable economy possible. One of these is a Japanese-based firm that has developed a method for greening roofs and other urban surfaces that uses hardly any water.
 
What the system does is slows down the process of water absorption and evaporation by capturing water in ice-cube-style trays below a surface of plants, soil and charcoal, according to Sean Johnstone, general manager of global business operators for Kawada Industries.
 
The system, which Kawada calls Midori-chan, also includes a layer of resin netting that ensures soil and charcoal doesn’t fall into the water trays, and most importantly, keeps plant roots out so they won’t soak up all the water at once. Instead, the charcoal absorbs water vapor from an air space between the water and the resin layer, and then “feeds” it slowly to the roots, according to Kawada.
 
A major building organization in Hong Kong is expected to use Kawada’s technology throughout the SAR, although the group has declined to comment on its plans at the moment. Kawada has performed tests for this organization for nearly two years, and has found more than 40 species of plants can grow relying on Hong Kong rainfall, and almost no additional water, Johnstone says.
 
Over a 21-month period, and in three phases, Kawada did 58 different tests, using different soil design mixes, soil depths, water storage unit sizes, plant species and mulch types, he says. The mulch makes it more difficult for weeds to take hold.
 
The system used 0.17 liters of water per square meter per month during the 21 months period. That compares with 189 liters of water per square meter per month consumed on a traditional green roofing system with the same plant species from July 2011 to April 2012, according to Kawada. The Midori-chan system used 0.35 liters per square meter per month in that shorter period.
 
Kawada is now doing 30 additional tests on another more types of vegetation, including herbs, plants used in Chinese medicine, vegetables, and fruits, he says. They are trying to learn how much water the various kinds of plants need, how much weeding and pruning is required, and what soil depths are best, among other things, so companies or government offices that use the system have a wide range of plant choices, he says.
 
Ideally, this system will expand beyond roofs to highway medians, planter boxes, and other places around the city that can use some greening up. As Johnstone notes, it would have the added environmental benefit of reducing the number of diesel-smoke-spewing watering trucks around town.
 
The Hong Kong government knows the benefits of greening urban spaces as it has boosted the abundance of variety of plantings across the SAR through various stages of the “Greening Master Plan.” Hong Kong’s Civil Engineering and Development Department, which oversees the greening plan, also emphasizes the use of vegetation whenever it upgrades man-made slopes.
 
The government can go a step further and look for a system of growing plants that uses as little water as possible.

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