Dear Colleagues,

This Special Issue seeks contributions focusing on the water–energy–food nexus along with the nexus contribution to resilience and sustainability of resources. While still in its first decade, the nexus concept has gathered significant momentum despite the lack of a clear unifying definition and a comprehensive mathematical model to conceptualize it. I envision this Special Issue to comprise a selection of papers focusing on five main nexus directions which I hope can form a roadmap to be followed in nexus research in the future:

1. Development of nexus modeling frameworks: Conceptual models from a wide range of modeling tools at all levels of complexity are needed. From simple Excel sheet simulations to advanced resource optimization models, the current literature leaves much to be desired in the area of nexus modeling. From model parameterization and boundary constraints to identifying unifying nexus objectives and dealing with model complexities, scaling-issues, and externalities, challenges to nexus modeling are numerous. Optimization, gaming, and multicriteria decision analysis are possible tools for addressing those open research questions, and contributions in those areas, among others, are highly welcomed.
2. Establishment of comprehensive nexus case-studies: Whether for education or research and model-validation, most nexus case-studies published lack comprehensive nexus parameterization, thus making it hard to be summarized in a few slides for education and classroom use, or for detailed model validation, which requires access to all the parameters used in any specific case study. Most nexus case-studies published so far focus on qualitative explanation of nexus case-studies (with only few parameters listed or tabulated), followed by more detailed analysis of results. This makes it a real challenge to summarize, interpret, or validate. In this Special Issue, all case-studies will be required to list their full parameterization in a clear (tabulated or in flow-charts) and detailed manner and are highly encouraged to add supplemental information or case-study summary in a few slides that can be cited and used for research and educational purposes.
3. Nexus impact and connections: While already a large concept to deal with, the nexus has already established connections with a wide range of natural, socioeconomic, institutional, and anthropogenic key components. As such, contributions connecting the nexus to health, governance, resource management, land use, and the physical environment are highly welcomed. Furthermore, contributions connecting the nexus to critical resources or constraints are very significant. For example, connections with the planetary boundaries concept connects the nexus with the nitrogen and carbon cycles as well as climate change. As such, contributions modeling those connections or assessing them are very significant.
4. Nexus scale and scaling issues: The nexus is highly scale-dependent and is highly impacted by the spatiotemporal production and distribution of resources, the geopolitical landscape, the uneven access to technology, as well as the socioeconomics of demands, supplies, and social habits. A global nexus exercise can lead to recommendations that may not apply at a level of a country and thus can require significant scaling efforts. Contributions targeting upscaling, downscaling or homogenizing the highly heterogeneous global landscape are highly welcomed. Case-studies can vary in scale from efficient production of food in a hydroponic farm at a farm scale all the way to the assessment of Sustainable Development Goals (SDGs) at the country to global scales.
5. Nexus education: Teaching the nexus is still a challenge across all educational levels. It is a concept that has made it in some specialized schools at the graduate level, but there has been very limited evidence of nexus education having any significant success in undergraduate or pre-college education. Contributions targeting the advancement of nexus teaching methods are highly welcomed.

Dr. Majdi Abou Najm
Guest Editor

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• nexus
• water-energy-food
• FEW
• optimization
• SDG
• resource management