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• First review that examines multi-actor approaches for WEFN systems. • Multi-actor approaches have been classified into four categories. • Only multi-agent based models enable operational decision making simulations. • Stakeholders must choose multi-actor approaches according to their needs. Water, energy and food are essential resources for human life; however, their security is increasingly threatened worldwide by climate change, urbanization, and population growth. The Nexus approach, conceptualized in 2011 by the Bonn Nexus Conference, addresses the interconnections and trade-offs of water-energy-food systems and analyzes the interdisciplinary and transdisciplinary dimensions of these systems with a systemic approach. This bibliographic review aims at showing how multi-actor perspectives and objectives on water-energy-food nexus systems are modeled together with socio-ecological considerations. It sheds light on the major techniques found in the literature to do so; mathematical modeling, participative approaches and multi-criteria decision-making. This paper identifies commonalities between models developed at similar spatio-temporal scales and decision levels. It also highlights literature gaps and outlines research challenges. [ABSTRACT FROM AUTHOR]

Given the significant energy consumption and carbon emissions associated with buildings, there is increasing interest in improving sustainability of building operations to reduce impact on climate change. A common goal is to operate buildings as "net-zero" energy users in which all energy consumed by the building is balanced against renewable energy purchased from the grid or produced on site. To achieve net-zero status, many buildings will require significant retrofit so as to both reduce energy consumption in the absolute sense and provide the remainder without consuming fossil fuels. Thus, multi-year planning is required to ensure that goals can be met on time. In addition, due to the inherent uncertainty associated with energy consumption and generation, actually achieving net-zero energy use may require discretionary curtailment actions to be taken, and deciding whether such actions are necessary can be challenging. To address these challenges, we propose in this paper a design optimization and operational planning strategy to make the decisions needed to achieve sustainability goals in buildings. The strategy can be applied to schedule design changes over a long horizon to meet annual targets, and it can also be applied in closed loop on a shorter horizon to determine whether curtailment is needed to stay on track. We discuss the formulation of the optimization problem, solution methods, and modeling approaches for key parameters. Application of the strategy is illustrated via examples. Overall, this approach will help automate planning that is often done manually, allowing buildings to take a significant leap forward toward achieving their sustainability goals. • Achieving sustainability goals in buildings requires multi-year planning. • The required design and operational decisions can be made via optimization. • Key problem parameters can be obtained from data-driven modeling. • The strategy allows sustainability goals to be met at minimum cost. [ABSTRACT FROM AUTHOR]