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.

Gardening on a rooftop is more than just a clever use of limited space.

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.

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