Urban food–energy–water systems: past, current, and future research trajectories

With the majority of the world's population living in urban areas, cities now drive global flows of food, energy, and water, with unprecedented implications for the sustainability of the planet and its people. This focus issue presents research on the nexus between food, energy, and water (FEW), as it relates to urban areas, broadly conceived. The eight papers in this issue are interdisciplinary, multiscalar, and cross-sectoral as they consider the effects of FEW interactions on the health of cities, their inhabitants, and the distant peoples and places from resources originate. This editorial summarizes topical areas covered by the papers, which include: a review of existing research on urban FEW systems and promising approaches; urban agriculture and energy-water dynamics; conventional agriculture and FEW dynamics; and the energy 'foodprint' of the American diet. The editorial concludes by identifying four crucial areas for further research: 1) ecosystem services associated with urban agriculture; 2) resource recovery in the urban FEW nexus; 3) equity, social actors, and governance of the FEW nexus; and 4) the food-energy-water-health nexus.