Forests In The Sky: How China Is Combating Air Pollution In Its Industrial Cities  

It’s that time of the year when yet another damning report on India’s worsening pollution crisis is released with a headline that momentarily jolts us into paying attention. 14 of the 15 most polluted cities are in India, screams the latest. Once we’re through the usual cycle of shock, outrage, and oblivion, it’s business as usual, even though everybody agrees that we need a drastic solution to solve our problem of worsening air quality. So far we’ve tried Compressed natural gas (CNG), even-odd, banning firecrackers, and vilifying farmers.

How about forests that eat smog and clean up the air?

Sounds great. But where’s the space to plant forests in the second most populous country on the planet? Certainly nowhere near its densely packed urban centers? Isn’t all that pollution coming from farmers burning stubble in their fields anyway?

Unfortunately, it turns out that it’s the world’s cities that are wrecking the planet. Even though cities account for only 2 per cent of the earth’s land area, they account for nearly 75 per cent of our carbon emissions. And yet we need our cities as much as we need our farms. An increasingly larger percentage of the world’s population is migrating to cities in search of livelihoods, and newer urban spaces are springing up every day to accommodate the flood of immigrants. 54 per cent of the world’s population lives in cities today, a number that is expected to go up to 66 per cent by 2050.

The world needs more urban spaces. And the world needs more forests.

What if we could have more of both?

An Italian design and construction firm has done just that by coming up with an innovative solution to the problem of reconciling our needs for urban spaces and our need for forests - forests built into urban structures.

Located in Milan, the design capital of the world, and also the most polluted city in Europe, Boeri Studio, led by its founder Stefano Boeri has pioneered the concept of growing hundreds of trees along with thousands of smaller plants onto tall buildings capable of housing residential as well as commercial spaces. In Milan, the twin towers known as Bosco Verticales – the vertical forests – have drawn wide acclaim from environmentalists, urban planners, policy makers, and architects alike for tackling a critical problem using technology and innovation.

Besides absorbing smog and keeping the air clean, the trees also regulate the temperature inside the building, keeping it cool during hot summer months and warm during the winters, leading to huge power savings.

Sounds exotic, like all things Italian. But is it feasible?

The Chinese are convinced that it is. In fact they’ve already bet a few billion dollars on it.

China has already contracted the designers of the Bosco Verticales, Stefan Boeri Architecti, to construct two such towers in its industrial hub of Nanjing. The two skyscrapers will collectively hold a total of 1100 trees and 2500 cascading shrubs. At the moment, the two towers will have a minimal effect on the pollution in Nanjing. The towers together will eat up about 25 metric tonnes of carbon dioxide(CO2) each year – the amount produced by 5 cars annually - and produce 60kg of oxygen.

The Nanjing buildings are however just the teaser - the Chinese are serious about combating pollution and are taking their fight to the next level. An entire forest city is under construction in Liuzhou city in the Guangxi province which is slated for completion by 2020. Called the Liuzhou Forest City, the project involves planting 40,000 trees and over 1 million smaller plants covering a complex of 70 buildings in the city planned for 30,000 inhabitants. To put that number in perspective, Delhi’s Lodi Garden, called the green lungs of Delhi, has a total of 7,055 trees spread over an area of 90 acres with no human habitation.

Every year the Liuzhou Forest City will absorb a whopping 10,000 tons of CO2 and 57 tons of other pollutants – enough to give a significant boost to air quality levels in even the most polluted of cities. Such a large concentration of flora will also have a lowering effect on the temperature of the region, besides contributing to increased rainfall and filtering out noise pollution. Imagine living being at your workplace and being able to hear birds chirping instead of honking of vehicles.

It isn’t just the Chinese either who are adopting this new innovation in urban planning. An upcoming project in Paris called the White City features a 54 meter high tower made entirely of wood and covered with over 2000 trees and shrubs - a green surface equal to one hectare of forest. Another tower coming up in Utrecht, Netherlands is planned to be 90 meters tall with 360 trees and 9000 plants and shrubs covering it. Expected to be ready by 2022, The tower will be able to absorb 5.4 tonnes of CO2 every year.

Similar projects are coming up in Taiwan, Toronto, and Bogota.

How Does it Work?

The design process involves collaboration between botanists and horticulturalists who suggest the type and nature of plants most suited to the particular project, and structural engineers who ensure that the structure is able to withstand the load imposed by the trees. The architect then incorporates the suggestions of the botanists and engineers into a clever design customized for the local conditions to balance maximum utilization of available space with minimization of energy consumption to come up with a sustainable design. The designs are tested in wind tunnels to ensure that trees would not be uprooted by gusts of winds and cause damage.

What happens when the trees grow up and begin to push through the roof?

The trees chosen for the project are selected on a number of criteria one of which is the height they are expected to grow to. Once chosen, the plants are pre-cultivated and allowed to get used to the conditions they would experience when they are transplanted into the actual building. Boeri terms this ‘intelligence’ of the flora – by exposing them to conditions of constrained vertical space, the plants learn to adapt remarkably well to the conditions they would be expected to grow in. A team of horticulturalists regularly supervises the plants to ensure if they need care or replacement.

Trees Make Their Own Rain - A Solution to the Urban Water Crisis

One of the most important potential benefits of urban forests such as the Bosco Verticales is solving the acute water crisis that faces most cities in the developing world. A recent study conducted in the Amazon rainforests by climate scientists from the University of California, Los Angeles, using NASA’s Aura satellite has found that trees are capable of making their own rain. While it was always believed that plants had some role in producing moisture, this is the first study of its kind that has convincingly demonstrated that a body of flora as large as an Amazon forest can produce enough moisture to produce rain bearing clouds even in the dry season. This rainfall can in turn have a domino effect on the weather. The falling rain releases heat from the warmed up surface of this earth which causes warm air to rise, trigger wind circulation and in turn helps more rain bearing clouds to form. We don’t yet know if it would be possible to create an urban forest large enough in scale to produce rain bearing clouds, but theoretically it seems a possibility. The extra rain water can be conserved using rain water harvesting techniques. More rainfall and more wind circulation would also contribute to cleaning up the air and drastically cutting down on air pollution.

Urban forests can also contribute to regenerating urban biodiversity. In Milan for instance, Swallows that had become rare in the city for decades have started to make an appearance in the vicinity of the Bosco Verticales buildings. Increased green cover will also have a noticeable effect on the local temperature. Studies have shown that the presence of a large number of trees within an urban area can lower the local temperature by upto 4 degrees Celsius.

All this sounds great. But surely these must cost a small fortune?

Not necessarily. An upcoming project being developed by Boeri in the Dutch city of Eindhoven is meant specifically for low income young couples. According to Boeri, the cost of these houses including the green cover, comes out to be 1300 Euros per square meter, less than half the average house price in the EU which stands at 3000 Euros per square meter.

Boeri has not patented any of this technology, preferring to keep it open for adoption and improvement by others. He approves of projects imitating his design that are fast coming up in Tokyo, Bogota, and other cities. Innovation and competition by a large number of players will further drive down the costs.

Bringing Nature Back into the City - Making Amends for High Modernism

The late nineteenth and early twentieth centuries were an era of high modernism – we built the foundation of the modern world by massive deforestation, damming of rivers, sucking out natural resources from the earth at an unprecedented rate – all enabled by breakneck advances in science and technology of that era. We now realize that it may not have been the most prudent approach for taking mankind forward, but it was what it was – a product of its times. The heady optimism unleashed by the scientific and industrial revolutions meant that man viewed all of nature as an obstacle to be overcome and as a resource to be exploited. While it may seem foolish, almost repulsive now, we must keep in mind that as late as the eighteenth century man was powerless against the forces of nature. Forests, swamps, and marshes overwhelmed whatever was left unclaimed and most forms of wildlife were a threat to human existence. Today of course we realize that we have sucked the planet dry with the excesses of the high modernist era of the early twentieth century.

For the last two centuries, cities have been expanding to conquer nature, overrunning the country side, sucking up precious resources. The city has become the enemy of nature at the same time that it has become the preferred natural habitat for the majority of mankind. The challenge for this century is to bring nature back into the city. It isn’t just a luxury anymore. It is a necessity. And as has been shown, it is now perfectly possible by the very science that brought us to this problem.