During the past few weeks we’ve planted a variety of food crops on various aspects of our green roof and wall systems. As such, I wanted use this blog entry to talk a little bit about the role green roofs could play in a system of urban food production, as well as highlight the growing importance of the city as a food producer.
Traditionally, cities have relied on their rural surroundings for their food. Not a lot of space in your typical human city has historically been dedicated to food production. As we come to terms with 21st century realities like climate change, resource limitations, and the urbanization of the global population, it becomes apparent that cities are going to need to produce more of their own food. Shifting food production into the cities will reduce costs associated with transporting, handling, and storing food, and also reduce waste. Reducing food wastage is going to be critical in forging a sustainable society. According to the FAO1, the carbon footprint of food wastage would rank it as the third largest CO2 emitter globally after the US and China, and it consumes an amount of freshwater equivalent to the discharge of the Volga. For the sake of visualization, here’s a picture of the Volga:
The United States is a big contributor to food waste, as the USDA reported that 31 % of the nation’s available food supply went uneaten in 2010, good for a loss of 133 billion pounds of food, $161.6 billion, and 1,249 calories per capita per day2. That’s the equivalent of an original sandwich from Chick-fil-A with a large fries, medium coke, and a side of buttermilk ranch sauce, for everyone in America, every day of the year.
Imagine if we actually ate all the food we ordered in this country
What might a food producing green roof in the city look like, though? Or better yet, what role could a green roof play as a component in a larger system of urban food production? Looking at Brooklyn Grange, a rooftop farm in New York City, we can see the answer to the first question.
The Grange has two farms totaling two and a half acres of space that produce 50,000 lbs. of vegetables each year. This is a good start, but vegetables aren’t enough to feed a city, nor can every roof be converted to an intensive vegetable garden. Thus, to answer the second question, I want to think about other concepts that can complement green roofs in urban agriculture.
One is simply converting existing green, public space to agricultural production. The city of Trier, Germany has undertaken a highly successful experiment in this field, creating what it calls an Edible City. The castle in the center of town is a large public space surrounded by parks, and now much of this park is devoted to producing food free to the public, including vegetables, herbs, and chickens. While there were concerns going in about vandalism and over-use by the public, but these were simply never borne out. People seem to respect this use of public space, and the project has increased in popularity every year. The crops are tended by formerly homeless or long-term unemployed individuals who use the program to develop employment skills and find work, which the majority of program participants had done when we visited. You can see how Trier looks below.
This public production of food could do a lot to reduce food wastage by increasing respect for and awareness of food production in individuals who would normally never think twice about where or how their food is produced.
There are also novel technologies that could be paired with green roofs for food production. Aquaponics is a form of production that grows both produce and fish. While it requires a green house, thus precluding its use in the same structure as a green roof, it produces large quantities of fish and produce with limited inputs. The fish provide fertilizer and carbon dioxide for the plants, while the plants provide nutrients and oxygen for the fish. A green roof built for farming could incorporate similar water recycling mechanisms to reduce the inputs needed. Regardless, aquaponics, vertical gardening, keyhole gardening, green roofs, and other new systems could combine some day to produce a meaningful amount of food within the city.
In addition to farming produce on a green roof, there is no reason why simple extensive systems couldn’t be used to raise livestock. While large animals obviously present challenges, green roofs seem like ideal environments to raise smaller stock like chickens. Lay-hens on such a roof could produce free-range, all natural eggs in the city, and converting rooftops to small scale meat production could lessen our reliance on industrial scale meat production with all of its environmental and ethical concerns. This is probably just the organic chicken farmer in me, but I think it’s possible.
There are, of course, other technologies and forms of production that could complement green roofs means of producing food in cities. Many of these are focused on producing as much food as possible in as little horizontal space as possible, which is obviously an objective of urban agriculture. Where green roofs present a novel opportunity is in converting existing nonfunctional space into productive space. Together, these technologies could reinvent our cities as leading centers of innovative, sustainable food production.