Singapore is an island on which only about 1,500 hectares of farm land remains, most of Singapore Island being taken up with urban apartment blocks, commercial buildings, industrial areas, plus parks and nature reserves. This picture shows the commercial buildings, but extensive dormitory suburbs of high rise housing can be seen in the background. It is the latter buildings, with flat roofs and extensive balconies, that "sky farm" bridges for growing food have been recommended.

When that happens it will influence myriad cities elsewhere.  Add to this rooftop opportunity the considerable food production potential in Singapore of:

• “Vertical farming” on the sun-facing walls of buildings;
• “Sky farms” on bridges between buildings;
• Intensive aquaculture in basements and at ground level.

This begins to outline a bold new opportunity for the global green roof industry currently developing strongly (and very reasonably) along non-food lines.  For what Singapore has in prospect today in food from the roof, the rest of the world will be offered tomorrow.

Major keys to this opportunity lie in food production technologies still developing, such as hydroponics, aeroponics and aquaponics – all of which better utilise fresh water.

Technology spin-offs from hydroponics and aquaculture are now expected to make Singapore, and my home town of Brisbane, in Australia, the two most likely world leaders in:

• Ground-level production of urban fin fish, crustaceans and mollusks in specially-designed containers, raceways or floating tanks using roof water runoff;
• Rooftop production of fresh vegetables, flowers and fruit from the wastes of such aquaculture – in a system named aquaponics;
• Tourism and education focused on the two technologies.

I predict that contributions in these fields in the two southern hemisphere cities will become as important as the admirable leadership in green roof development that Toronto, Canada, is now well showing in such things as building insulation, better handling of roof water runoff and aesthetics.

Both green roof streams are new business opportunities well worth grasping as climate change factors require the urgent attention of all of us – even if it’s on the principle of doing something “just in case.”

Let’s look at what is in prospect in Singapore to see how the future of our own cities on most parts of the planet can be glimpsed as if in a crystal ball.

A survey by Ngee Ann Polytechnic students supervised by their hydroponics lecturer Gregory Chow, found that four suburban areas of northern Singapore -- about one tenth of the total built environment -- had about 212 hectares of apartment and commercial rooftops to grow fresh vegetables, using inorganic hydroponics.

Extrapolation of this across the whole of Singapore reveals that that around 1,000 hectares of rooftop space could be available (relatively easily) for urban food production in Singapore.

Gregory Chow calculated that about 39,000 tonnes of vegetables a year could be produced from the 212 hectares he and his students studied. If these vegetables were sold for around $2/kg – the value of produce would be around S$40 million a year - approximately U.S. $ 23.5 million a year.

Given that the Singapore Government’s objective is to displace around 20% of the annual consumption of 380,000 tonnes of fresh vegetables consumed each year with local production (currently at only 5% pa of the total), this Ngee Ann Polytechnic study is significant justification for more serious analysis of rooftop production of fresh vegetables across the whole of Singapore.

It is reduction of so-called “food miles” writ large!

Gregory Chow has demonstrated already, what can be done in rooftop farming with his award-winning project on the atrium of the 800-bed Changi General Hospital, below.

The Ngee Ann findings and the Changi Hospital example highlight the great need for a similar economic study of the potential of another Singaporean innovation – the “sky farm” concept, which would blend in well with both the food-producing potential of Singapore’s rooftop spaces, plus the potential of “vertical farming” down the sunlit faces of apartment buildings.

Professor Lee Sing Kong, Dean, Graduate Programmes and Research, National Institute of Education, of Singapore’s Nanyang Technological University, has been advocating “sky farms” that use the aeroponic technology so well pioneered by Singapore’s AeroGreen Technology Pte Ltd., initiated by the Sime Derby company.

Aeroponics is where a hydroponic nutrient solution is sprayed onto plant roots dangling in light-proof boxes. It allows temperate-climate fresh vegetables to be produced economically in tropical and sub-tropical climates.

Professor Lee’s good idea is sunlit bridges between high-rise apartment buildings or even office towers. They could be retro-fitted as single or double units at first or second-floor levels, or part of a tier of vertical structures servicing the food (and organic waste management needs) of multiple stories.

Aeroponic vegetable production on the bridges would use nutrient solutions stored and cooled at ground level, then piped to light-proof boxes above. The “sky farm” bridges can thus be relatively light structures.

The significant saving with this system is the cost of farm and transport energy (mostly diesel fuel) and consequent air pollution with diesel particulates that are known to cause asthma, emphysema and even cancer – particularly in the very young and the elderly.

Tenants of the buildings would be able to harvest the temperate-climate or tropical-climate vegetables themselves, perhaps in co-operatives similar to the one already operating a rooftop hydroponic unit at Singapore’s Tanjong Pagar apartment complex, see below.

It is my contention that Singapore could produce, most economically, at least a third of its future fresh vegetables from rooftops and “sky farms.” It may choose never to replace all imports, on either practical (e.g. potatoes) or cost grounds.

But in well utilising its rooftop resources it would provide the world with an important demonstration of how urban agriculture, designed into buildings, could greatly enhance the food security of many cities in the tropics and sub-tropics – and provide stimulus for further food-from-the-roof technology to be developed in other climates.

Besides taking up the good ideas of their own citizens, Singaporeans also need to look closely at the new equipment from Australia that is being developed for sub-tropical and tropical hydroponics, aquaculture, aquaponics and vermiculture. This equipment is capable of being meshed into urban agriculture that:

1. Has urban organic wastes changed into organic plant nutrients or organic fish feed in basements and at ground levels.
2. Has the waste by-products (e.g. excess worms or insect larvae) being fed to fish, crustaceans or molluscs growing in tanks or containers.
3. Has organic hydroponic growing of food plants on nearby rooftops (via piped nutrient solutions of fish wastes and worm liquors, refined via microbial action).
4. Has water being recycled to fish and crustacean tanks minus the plant food, and with superior aeration.

The photo at left shows a sub-tropical hydroponic farm growing bok choy in Brisbane, Australia using clip-together oval channel equipment under hail netting. It is the kind of food-from-the-roof technology likely to be adopted for Singapore rooftops - with the hail netting serving as a worker safety net, plus a barrier to rooftop debris flying away with wind gusts. An acre of this kind of hydroponics is more productive than six acres of good soil -- using less than a 10th of the water.

So Singapore's 1,000 hectares (2,500 acres) could be equivalent to more around 6.000 hectares (15,000 acres) of soil horticulture. What's more, the roof-grown fresh food is close to where it is needed above apartment blocks or restaurants -- thus saving substantial transport energy costs.

Singaporeans also need to look at the innovations in aquaponics now well confirmed in their great good sense in Canada and the United States – where rooftop growing of food is observable, but has yet to be given the technology thrust it needs.

Australian and North American companies involved in various forms of aquaponics via floating tanks or raceways will also have interesting options to offer Singapore, in both fresh-water and salt-water systems that combine the growing of fish (and other aquatic food animals), with the growing of food plants that can utilize their wastes, in rooftop farming and gardening, or on sunlit sides of buildings.