The food-water-energy nexus and green roofs in Sao Jose dos Campos, Brazil, and Johannesburg, South Africa

Green roofs affect the urban food-water-energy nexus and can contribute to sustainability. The authors develop a generalizable methodology and framework for data-sparse cities to analyze the FWE nexus of green roofs, integrating environmental costs and benefits and tracing energy-water-carbon footprints across city boundaries. Applied to São José dos Campos (Brazil) and Johannesburg (South Africa), they find green roofs are essentially carbon neutral and net energy consumers over their life cycle. SJC is a net water beneficiary while Johannesburg is a net water consumer. Utilizing rainwater can save irrigated water but requires 1.2 times more energy than tap water. The results suggest SJC and Johannesburg should prioritize local food production and energy saving, respectively, highlighting opportunities for urban green roof practices.

Fanxin Meng, Qiuling Yuan, Rodrigo A. Bellezoni, Jose A. Puppim de Oliveira, Yuanchao Hu, Rui Jing, Gengyuan Liu, Zhifeng Yang, Karen C. Seto