(109a) Review and Perspective on Nexus System Analysis

As the global population grows and increasingly lives in cities with lifestyles based on greater material consumption, more attention is being given to the integrated system that supplies our food, energy and water, the Nexus. The interaction between these three essential commodities can be seen in many ways. For example, production of sufficient food requires use of man-made fertilizer, to an extent that food and energy prices have become linked. Agriculture now accounts for 70% of water withdrawn from aquifers, streams and lakes. In many places fresh water is critically constrained, which affects our ability simultaneously to produce more food, grow crops for biofuels, and maintain natural ecosystems. And there is mounting concern about the effects on the Nexus of climate change, itself largely the result of fossil fuel consumption and land-use change (for agriculture).

Evidence for this growing interest in the Nexus is illustrated by a review of published literature (1). Over the 5-year period 2011-2016 the rate of publication of studies on the Food-Water-Energy Nexus in the scientific literature grew by a factor about ten. These publications underline the importance of Nexus concerns to policy-makers, transnational and regional institutions, and business/commerce. The study purposes of this body of literature can be summarized as

• reviews and Nexus issue discussion papers;â?¨
• quality-of-life studies to understand Nexus trade-offs or develop responses to achieve sustainability objectives (e.g., human well-being, healthy ecosystems);â?¨
• product studies to understand Nexus implications or develop responses related to providingâ?¨products (e.g., a renewable energy technology, a service such as clean water); andâ?¨
• studies to develop integrated system modelling tools.â?¨

Case studies tend to be of two types: those related to regional development, and those related to specific sectors. So Hoffâ??s (2) background paper for the Bonn2011 conference outlines ten Nexus case studies, including Jordan and Ethiopia, the arid Ningxia region of China, and Gujarat. The Brazilian Cerrado savanna area offers a study in the competition between biofuel and food crops for land and water resources; the Nile Basin offers the same trade-off, with hydropower also playing a role (2). Responses by several companies to Nexus challenges in their own business areas are outlined in a report by Conservation International (3). These responses cover a wide range of policies and activities, but there are several common themes, including

• developing greater resource efficiencyâ?¨
• conducting resilience planning for price volatility and climate changeâ?¨
• systems thinking to design synergistic solutions (e.g., business decisions that also yield multiple environmental and social benefits)â?¨
• gathering new data to understand current and future trendsâ?¨
• stakeholder engagement to better understand the Nexusâ?¨
• ecosystem valuation to help decision-making and balance trade-offs.â?¨

Particularly important in view of the trend of more people to live in cities are the (relatively few) studies of the â??Urban Nexusâ?, dealing with what may be termed the â??metabolismâ? of the city. It is concluded that this metabolism, a hybrid of natural and artificial structures presents an opportunity for greater efficiency through better design and regulation. At present it is poorly understood, and studies are hampered by lack of data.

Case studies show the vital role played by stakeholder involvement in clarifying issues, priorities, and values. They also demonstrate the importance of an integrated systems view of the complex interrelationships of the Nexus when planning effective remedies. Assessments conclude that transformative social and political change is needed to create new structures, markets, and governance to deal with the Nexus if we are to meet agreed-upon sustainable development goals.

Needs for the future of Nexus studies include

• the publication of more case studies, particularly including stakeholder involvement;â?¨
• the creation of new frameworks and methodologies of analysis, including some that will integrate societal, environmental, and technical dimensions;
• the development of modelling tools accessible to a wider range of investigators (at present these tend to be highly specialized);â?¨
• the promotion of best practice in Nexus evaluation and effective use of study results;â?¨
• improved accessibility of Nexus data;â?¨
• metabolism modelling and engineering for the urban Nexus; andâ?¨
• promotion and support from funding agencies and institutions for multidisciplinary and multinational studies of Nexus analysis, issues, and applications.â?¨

(1) Keairns DL, Darton RC, Irabien A 2016 The Energy-Water-Food Nexus Annu. Rev. Chem. Biomol. Eng. 7:239â??62

(2) Hoff H. 2011. Understanding the Nexus. Background Paper for the Bonn2011 Conference: The Water, Energy and Food Security Nexus. Stockholm: Stockholm Environ. Inst.

(3) Gerholdt J, Pandya S. Resources: The Energy, Water, Food Nexus. Arlington, VA: Conserv. Int. Bus. Sustain. Counc.