Thousands of years of development have made the production and consumption of water, energy, and food for urban environments more complex. While the rise of cities has fostered social and economic progress, the accompanying environmental pressures threaten to undermine these benefits. The compounding effects of climate change, habitat loss, pollution, overexploitation (in addition to financial constraints) make the individual management of these three vital resources incompatible with rapidly growing populations and resource-intensive lifestyles. Nexus thinking is a critical tool to capture opportunities for urban sustainability in both industrialised and developing cities. A nexus approach to water, energy, and food security recognises that conventional decisionmaking, strictly confined within distinct sectors, limits the sustainability of urban development. Important nexus considerations include the need to collaborate with a wide spectrum of stakeholders, and to “re-integrate” urban systems. This means recognising the opportunities coming from the interconnected nature of cities and metropolitan regions, including links with rural environments and wider biophysical dynamics.

Secure and efficient supply for the food, energy and water resources is essential for sustainable urban development. Due to the close interaction of food, energy and water systems, it is necessary to analyze food-energy-water nexus from an integrated perspective. Taking the Detroit Metropolitan Area as a case, this study first constructs a food-energy-water physical input-output model to quantify food, energy and water flows. Then, structural path analysis is adopted to identify critical supply chain paths driven by the final demand of key sectors. Quantitative results of food-energy-water flows show that major inputs of food and energy in the Detroit Metropolitan Area are from outside through imports, while water use is predominately extracted from local sources. Local consumption activities for the food, energy, and water systems are mainly concentrated downstream of the supply chain. Structural path analysis results show that intermediate processes use relatively large amounts of food, energy and water, and should be more concerned. Also, identifying sectors involving multiple systems, such as Food Processing, Domestic Consumption, Solid Waste Management, Wastewater Treatment, and Residual Processing, can promote co-benefit opportunities. This holistic view on urban FEW nexus presented in this study can facilitate better decisions and help avoid unintended consequences.

In the process of urban agglomeration, water-food security can be deemed as a key to support urban development and human living, but which can be challenged by expanded population growth, accelerated industrialization, unbalance regional economic development and diversity of weather (due to climate changes). In this study, a water resources allocation and food production (WF) optimization is developed for regional sustainability under multiple uncertainties. A hybrid two-stage fuzzy programming with Laplace criterion (TSFL) is proposed into a WF optimization to handle hybrid indeterminacies, which can increase the robustness of decision-making. The WF optimization with proposed TSFL method can be applied to a practical case of Beijing-Tianjin-Hebei (BTH) region. The obtained results associated with water deficits, optimal water allocations, inadequate capacities of food production, rational irrigation schedules, sound livestock scales, optimized agricultural possessing layouts and system benefits under various population-economy regulation scenarios can be obtained. The results can reflect the tradeoff between economic development and water-food safety; meanwhile, they can display risk violation of WF plan under various credibility levels and Laplace criterions (based on TSFL method). All above results can facilitate to produce an optimized water-food plan to support the synergetic development of BTH region in a robust manner.