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 megacities such as Cairo and Dhaka, Bangladesh, the lack of green space contributes to a host of problems: increased air pollution, higher air temperatures, and greater exposure to ultraviolet radiation, all of which are making these cities increasingly dangerous places to live. According to the World Health Organization, outdoor air pollution kills 4.2 million people every year, most in low- and middle-income countries. Outdoor air pollution is particularly deadly in dense urban environments in these nations. 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.

Why do cities like these lack green space? The natural environment often plays a role: Cairo, for example, is in a desert; it’s not naturally lush. Rapid urbanization in recent decades has also led to the development of informal neighborhoods and other new construction projects, exacerbating the problem. But mostly, it comes down to planning.

For postcolonial cities, formative urban development occurred under colonial domination and focused on exploitation. Urbanist Garth Andrew Myers, author of Rethinking Urbanism: Lessons from Postcolonialism and the Global South, writes that “cities were predominantly oriented around the extraction of goods for the metropole.” They were never designed to be sustainable.

Even today, foreign powers shape the development of postcolonial cities in pernicious ways. China’s Belt and Road Initiative is littered with examples of foreign development projects that have caused environmental destruction and left developing nations with untenable debts. From 2015 to 2017, Egypt borrowed $1.03 billion from China to finance infrastructure projects. But much of this recent development has ignored the threat of a warming climate, which is causing temperatures to rise, drought conditions to worsen, and extreme weather events like flash flooding and sandstorms to become more common across the nation.

Informal settlements, home to the cities’ most impoverished and marginalized communities, are the most vulnerable to rising temperatures, ultraviolet radiation, and air pollution. These neighborhoods have multiplied in both Cairo and Dhaka since the turn of the 20th century, and they often lack proper infrastructure and access to green space. “Some areas in informal settlements have zero square meters per inhabitant of green space,” says Abdallah Tawfic, co-founder of Cairo-based organization Urban Greens.

These patterns hold true for many of the Global South’s largest cities. But organizations like Urban Greens as well as Schaduf in Cairo and Green Savers in Dhaka are committed to greening their cities by weaving rooftop gardens into the crowded cityscapes. 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.

Gardening on a rooftop is more than just a clever use of limited space, though. Rooftop gardens have substantial positive effects on air pollution and city temperatures. “Having a green cover is the best thing that could happen to this environment,” says Khaled Tarabieh, professor of architecture at the American University in Cairo.

Cooler, Cleaner Cities

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.

In Jeddah, Saudi Arabia, one of the world’s hottest cities, a study showed that indoor air temperatures in buildings with rooftop gardens were as much as 12 degrees Fahrenheit cooler than those without gardens, even during the warmest hours of the day. That saves on energy, too, which can have knock-on environmental effects. Research also shows that even relatively small rooftop gardens can reduce surrounding air temperatures by more than half a degree Fahrenheit.

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.

Rooftop gardens are also more practical than green walls or roofs, which are mounted on buildings. Green walls may be on-trend, but Tarabieh says these spaces often require more water than a rooftop garden of the same size, are much more difficult to maintain, and can even compromise the structures on which they are mounted.

Green Savers has worked on more than 5,000 rooftop gardens in Bangladesh since its founding in 2010. Most of its projects have been in Dhaka, the nation’s capital and one of the most densely populated cities in the world. But it has also expanded to the cities of Cox’s Bazar and Sylhet.

Urban Greens is a much younger enterprise, but it’s growing fast. Founded in 2018, the organization partners with sponsors to provide hydroponic gardening supplies to low-income families for free and sells these same supplies to other customers. Interest in home gardening skyrocketed during the pandemic so the sales side of the business took off, according to Yahia El-Masry, the organization’s co-founder and business development manager.

Reinvesting those profits has allowed Urban Greens to expand faster than anticipated. It is now launching new projects in Upper Egypt and a website called the “Urban Greens’ Network,” which it hopes will inspire more Egyptian city dwellers to begin gardening. “We want to create a network of practitioners to share knowledge and information and at the same time, invite other people,” El-Masry says.

Tending Community Health

Beyond rooftop gardens’ environmental benefits, they can also provide food and income to the families who tend them. Those are the goals of Schaduf, another Cairo-based organization working in urban agriculture. “Environmental and social change are both in the vision for the company,” says Malik Tag, the organization’s business development manager.

Schaduf, founded in 2011, establishes produce-bearing rooftop gardens for Egyptian and migrant families in informal neighborhoods. The families that receive training and equipment from Schaduf grow gourmet leafy greens and herbs, and Schaduf connects them with upscale supermarkets to sell their produce for the best possible price.

In response to Bangladesh’s high youth unemployment rate, Green Savers has also embraced a social mission, hiring and training young people as “plant doctors” to tend to rooftop gardens.

The greatest challenge for all three organizations has been convincing funders and local residents that the cost and effort of maintaining rooftop gardens are worthwhile. This is particularly true for those peddling hydroponic systems, which come with a higher startup cost. But the organizations have all had success increasing interest through community workshops and school programs. “We found that kids are really interested,” Rony says. Many students, after learning about rooftop gardens in school, have convinced their parents to research them further.

As global temperatures continue to rise, megacities like Cairo and Dhaka will require more significant interventions than urban agriculture alone to prevent air pollution and temperatures from increasing to unlivable levels. But initiatives to green these cities are an excellent place to start. As Tarabieh puts it, green rooftops may not solve all the cities’ problems, but, “Will it give us an advantage? Absolutely.”

Editor’s note: This story was originally published in Yes! Magazine. It appears here as part of the SoJo Exchange from the Solutions Journalism Network, a nonprofit organization dedicated to rigorous reporting about responses to social problems.