Toward the Nexus Equation: A Conceptual and Mathematical Framework for Energy-Water-Food Nexus Analysis

Abstract:

Water, energy, and agriculture depend on each other so strongly that attempts to achieve sustainability in any of those three domains will directly impact the others. These interdependencies, collectively known as the Water-Energy-Food Nexus, become more complex and more critical as the climate changes, the population grows, habits and lifestyle alternatives, and the prices of water, energy, and food increase. The U.S. National Intelligence Council has identified the nexus of water, energy, food, and climate change as one of four overarching megatrends that will shape the world in 2030. However, the global research community has rarely addressed the full problem and focused instead on different subsets of the problem. For example, interactions between two of the three domains were studied, often neglecting the impact of such interaction on the third domain. Investigators have quantified water-energy tradeoffs in the highly engineered, centralized systems of water and power management. Agricultural researchers have tracked water costs by applying the concept of virtual water (the total volume of water needed to produce and process a commodity or service) or using large-scale system models to investigate food and water security. Integrative nexus initiatives have focused on reviews and data collection of existing knowledge and relevant facts. They unfortunately lack a conceptual and mathematical framework that can integrate all the gathered knowledge and account for multiple interactions, feedbacks, or natural processes that occur across all three domains of the nexus. Here, we present an integrated conceptual and mathematical framework (roadmap) for the nexus. This framework is driven by spatiotemporal demands for water, energy, and food to be satisfied by resource management of the three domains, envisioned as a stepwise process, with each step requiring inputs from the three nexus domains and creating waste products. The efficiency of each step, combined with mass balances, create the linkages and feedback loops within the nexus. Such an approach allows for a compact, single representation of the ’nexus equation’ that generally represents all interactions, material pathways, feedback loops and embedded resource echoes.