Preliminary Study on Detroit’s Urban Food-Energy-Water (FEW) Nexus

With 66% of the world’s population expected to live in urban areas by 2050, cities around the world will face numerous challenges in sustainable provision of food, energy, and water. These challenges are particularly complex due to the interconnectedness of the food system, energy system, and water system. For example, water is required for food and energy production; energy is needed for food production as well as water and wastewater treatment and distribution; and industrial agriculture and food production lead to oversupply of nitrogen and phosphorus in the urban water system through fertilizer use. Therefore, policy and technology solutions addressing urban food-energy-water (FEW) challenges need to be evaluated through the lens of FEW nexus to identify co-benefits and avoid unintended consequences. This calls for innovative approaches to model the urban FEW nexus as an integrated whole, instead of examining them individually.

Existing studies primarily investigated urban FEW systems individually (e.g., nutrient flows, energy flows, and water flows) or focuses on two of the three FEW systems (e.g., water-energy nexus and food-water nexus). Existing studies that consider all FEW systems primarily aim to understand the impact of one system on the other two, such as how urban water-sector innovations change food and energy flows. There lacks an integrated approach that characterizes the comprehensive interdependence of urban FEW systems.

In this study we developed a systems modeling framework for the urban FEW nexus. We also applied this framework to the Detroit Metropolitan Area (DMA) as a preliminary study. The urban FEW systems modeling framework we proposed is based on material and energy flow analysis (MEFA) which quantifies flows and stocks of a group of substances within a system during a given period of time. This framework includes three steps:

Step 1: Individual FEW systems are modeled as resource flows across major sectors (e.g., water treatment, wastewater treatment, food production) of the urban system. Given the variety of food crops and products, we used nitrogen and phosphorus flows as the currency to represent the food system. Quantities of resource flows (water, energy, nitrogen, and phosphorus) are estimated based on a variety of data such as population, water withdrawal, and wastewater generation that were collected for the DMA case study.

Step 2: We identified and measured interdependence of individual FEW systems. This was done through literature review for common FEW interactions and quantitative estimation of resource flows between individual FEW systems (e.g., the amount of water used for food production and energy production).

Step 3: Each individual FEW system is characterized as a network of resource flows. Based on the interconnections between individual resource flow networks obtained from Step 2, we integrated the individual FEW resource flow networks as a network of four networks (water, energy, nitrogen, and phosphorus). This provides a mathematic representation of the urban FEW nexus, which will be the base of further analysis and modeling.