Urban food-energy-water nexus indicators: A review

•Coordinated efforts are often deemed critical to minimize trade-offs, while maximizing synergies in use among FEW.•All the nexus indicators can be classified as flux; structural; environmental impact and efficiency indicators.•Results highlight the necessity of developing new indicators.•It would be vital to incorporate as many flows as possible, to represent urban systems as a whole. The unprecedented surge in urbanization and population growth rates is generating multiple impacts, affecting food, energy and water (FEW hereafter) demands. Moreover, the adverse effects are extending to climate, as well as to human and ecosystem health. Coordinated efforts are often deemed critical to minimize the trade-offs while maximizing the synergies in the use and the effective analysis of the interlinkages among food, energy, and water within urban ecosystems. Data are collected and transformed into useful information through different indicators, which are often applied to guide several policies in the urban domain. However, their different nature now asks for a critical reanalysis to collate them into different groups, understanding their guiding principles and identifying possible gaps for further policy- and design-oriented studies. This paper reviews the state-of-the-art on existing urban FEW nexus indicators. Indicators were found to belong to four main distinct groups, measuring resource fluxes (52%); quantifying environmental impacts (13%), and efficiency aspects (29%). Results highlight a need to develop new indicators, considering the inclusion of all involved factors within new integrated metrics. However, prior to developing an overall sustainability indicator system is presented, it would be vital to incorporate as many flows as possible to represent the entire urban systems.