The rooftop farm at the Bank of America Tower in Central

Urban farming, usually done on rooftops, has been gaining traction around the world. Its rise can originally be traced to increased awareness of CO2 emissions that result when our food travels hundreds, if not thousands of kilometres from the farm to our table. Leisure vegetable gardening on rooftops has been gaining popularity among city dwellers in Hong Kong. Gardening however, while highly beneficial, cannot scale to address environmental challenges we face. Are production rooftop farms a viable option in mitigating some of these issues?

A HKU paper examining green roofs (which includes rooftop farms) concluded that:

“Apart from enhancing the city landscape and environment, mitigating the urban heat island effect and improving air quality, green roof can improve the microlimate and increase the life span of waterproof and insulation facilities on the roof. Consequently, roof greening with a sufficient large scale is conducive to energy conservation and life cycle cost saving for the urban city.

Green roofs can help reduce three of the four top problems facing the society in the next 50 years: energy, water, and environment. In this way, the green roof technology has a potential to improve quality of population health and welfare in the urban areas with dramatically reduced vegetation.”

In addition to the benefits created by generic green roofs, rooftop farms can make a dent in Hong Kong’s reliance on imports for almost 98% of its fresh vegetables. Vegetables however requires more water to grow and pumping water up a 30 story building will reduce the energy savings of green roofs. Fortunately, growers can mulch (cover) the growing surface to reduce evaporation and install rainwater collection systems to significantly reduce the consumption of tap water.

In addition to reducing the carbon footprint of our food, urban or rooftop farming also provides fresher, more nutritious produce for consumers. According to this Harvard paper, “foods grown far away that spend significant time on the road, and therefore have more time to lose nutrients before reaching the marketplace.”

Urban farming can also help to address the issue of our ever expanding landfills. Food waste constitutes almost 40% of total landfill waste. This food waste can instead be composted to produce a growing medium highly sought after by organic growers. In Hong Kong, most food waste is not used to make compost in part because there is insufficient local demand for it. Urban farms can create demand for compost, thereby reducing the amount of food waste entering our landfills.

Increasing demand for food waste compost has two other positive side effects. First, as a superior growing medium it can reduce demand for fertilisers. Second, dumping food waste into an anaerobic environment, such as a landfill, produces methane, a greenhouse gas 16 times more powerful than CO2. Composting can reduce the climate change impact of landfills.

While urban farming can help address many of our environmental issues, there remain many challenges that make widespread implementation difficult. In a future article, we will explore these challenges and share our lessons learned.