Rooftop gardens for cooler, cleaner megacities

Inspiring stories from three organizations, in Egypt and Bangladesh, who promote and help the installation of rooftop gardens in megacities lacking green space.

Cairo and Dhaka are the two cities used as examples in that article but also represent most non-western megacities in the challenges they face. Partly because of colonization (cities were viewed simply for extraction, not as sustainable living spaces), partly because of bad planning even later on, and partly because of tightly and haphazardly built informal settlements, they find themselves with very little green spaces, resulting in more heat and pollution, in turn resulting in worst health.

The view of Cairo from the air is one of concrete buildings and tangled overpasses stretching as far as the eye can see. Green areas comprise less than 4% of the total urban built area, and recent construction projects have resulted in the destruction of tens of acres of the city’s already-sparse green space. […]

In Cairo, for example, researchers estimate that 19% of non-accidental deaths in people over the age of 30 can be attributed to long-term exposure to two common air pollutants: nitrogen dioxide and fine particulate matter (PM2.5). That’s an estimated 20,000 deaths each year in this city alone.

But dense cities also mean lots of roofs, and organizations like Urban Greens as well as Schaduf in Cairo and Green Savers in Dhaka are trying to turn as many of those roofs as possible green.

The inspiration behind their projects is simple: “We don’t have the space to plant trees, but we have 500,000 rooftops capable of taking the load of a rooftop garden,” says Ahsan Rony, founder of Green Savers.

With more green roofs, those neighbourhoods get less heat (directly and limiting the radiated heat at night), filtration of some of the pollution, and in some cases new income by growing and selling what they grow on their roofs.

When a rooftop has a green cover, comprised of plants in raised beds, tables, or trellises, it shades the apartments on the upper floor, preventing overheating, especially in buildings that lack proper insulation, as is often the case in informal settlements. Rooftop gardens also reduce the heat that concrete structures absorb throughout the day and then re-emit at night, keeping cities cooler overall. […]

With cooler temperatures, less ground-level ozone forms, reducing outdoor air pollution. Studies also show that plants can remove ozone, particulate matter, sulfur dioxide, nitrogen dioxide, and carbon monoxide from the air. “If you are living in a place where you have a thick green cover, you’re enjoying a better and healthier quality of life,” Tarabieh says.

They are also locally founded, employ local people, and develop innovative combinations of business models to sustainably continue their missions. Win/win/win/win.

Photo: Cairo-based organization Schaduf helps city dwellers grow leafy greens in hydroponic rooftop gardens, image from Schaduf.