Megacities: Shades of green

More than two-thirds of people will live in urban areas by 2050, according to the United Nations — but only some will live in cities where they can also enjoy nature. With just 2.2% of its land dedicated to public parks and gardens as of 2015, the Turkish city of Istanbul is one of the least green cities in the world. The government has proposed turning old public spaces into parks.

Figures collated by the World Cities Culture Forum show stark differences in urban planning in cities around the world. In Shenzhen, China, green space accounts for 40% of the cityscape, despite a booming construction sector that has dotted the city with skyscrapers. The crowded capital, Beijing, also says it's working to increase its urban green space, which is currently at more than 45%.

Parks encourage people to exercise. Spending time among the sights and sounds of nature is also linked to better overall mental health. It relieves stress and improves well-being, as well as promoting social interaction. Despite its reputation as a concrete metropolis, about a quarter of New York City is green, with more urban gardens popping up on former industrial sites for residents to enjoy.

Trees and plants also clean the air, so green spaces effectively make it safer to breathe. This is especially important in crowded cities like Tokyo, which according to a 2015 Bureau of Urban Development survey has just 7.5% green space. With a population of 9.2 million, many of whom are elderly, Tokyo's citizens are vulnerable to air pollution.

Concrete heats up cities and makes citizens more vulnerable to heat waves. This is called the urban heat island effect, meaning cities are typically much warmer than the surrounding land. But green spaces are a solution to this problem, as they help cool urban areas. Although public parks account for 35% of space in Los Angeles, the dense city is very familiar with the urban heat phenomenon.

Green spaces also absorb water to help prevent the kind of flooding seen in 2018 in Paris, some 9.5% of which is made up of green space. Engineered green spaces can even capture and purify stormwater runoff while protecting residential areas, making them a critical part of a city's flood management system. Paris is working toward planting 20,000 new trees by 2020.

Most emerging megacities, defined as having a population of more than 10 million, are in the global south. Bogota, Colombia, is a booming metropolis that dedicates 4.9% of its land to green spaces. As cities grow bigger and richer, they need to balance short-term economic development with the long-term health of citizens and the impacts of climate change.