Douglas Broom, Senior Writer of World Economic Forum writes:

High above the streets of New York, more than 36 tonnes of organic vegetables are grown every year. And the farms that produce them aren’t just feeding residents – they’re helping to stop sewage polluting the city’s rivers too. Covering a total of 2.3 hectares (5.6 acres), the farms sit on top of three historic industrial buildings. Their soil is just 25 cm (10 inches) deep, but it absorbs millions of litres of rainfall each year – water that would otherwise flush straight into the city’s drains.

New York has long had a problem with what is known as Combined Sewer Overflow, where rainwater inundates water treatment plants causing the sewers to overflow directly into the Hudson and East River.

Green roofs help urban areas reduce the heat that otherwise radiates on summer nights from conventional rooftops. That not only helps to make the city cooler in summer but also reduces the amount of energy needed to keep the buildings cool.

Brooklyn Grange, which operates the three rooftop sites, built its first farm in 2010. It broke even in its first year, moved into profit two years later and now employs 20 full-time and 60 seasonal staff. Its founders believe commercial urban agriculture can help cities become cleaner and greener. And they measure their success against a “triple bottom line” – profit, the environment and impact on people.

The rooftop farms use waste food to produce compost. Half their produce is sold to restaurants and they run two weekly markets and deliver locally through a community-supported agriculture scheme, which connects farmers directly to consumers. They are home to 40 beehives, too. The farms have so far hosted 50,000 young people on educational visits to learn about sustainable city farming. They run public courses on everything from sustainable dye-making to making hot chilli sauces. They host yoga classes and even weddings. The company has now expanded into designing and building mini farms and wild flower gardens for private clients across the city.

Brooklyn Grange’s Rooftop Farm #2 at the Brooklyn Navy Yard is a win-win-win, reducing stormwater runoff, creating local jobs, and providing access to fresh produce for the community.

Read more: New York's rooftop farms provide fresh local produce - and help stop a sewage problem