Supplementary Material. Spatial and temporal synchronization of water and energy systems: towards a single integrated optimization model for long-term resource planning

Feedback between the water and energy sectors exist across system life-cycles and link the resources both spatially and temporally. Tracking the impacts of policies made in one sector on the other can thus be complicated and several nexus methodologies have been developed to address these issues. However, the different physical, temporal and spatial characteristics of the water and energy systems present several hurdles including identifying which of the many links between the two systems to model, with what detail to represent each system and how to synchronize the temporal and spatial differences while simultaneously dealing with data scarcity and large uncertainties. This paper addresses some of these issues and presents a fully integrated hard-linked water-energy linear optimization model. Keeping in mind the varying needs of different stakeholders, the model is deliberately made flexible, allowing users to modify objective function sub-component weights as well as providing adjustable spatial and temporal scales. Additional system processes and end-user technologies can be added to the model while existing representations can be further refined depending on the detail required. The capabilities of the fully integrated model are investigated in an example case study for Spain. The performance of the model run in an integrated mode is compared to that of the model run in a non-integrated mode without any inter-sector links. An integrated approach is shown to have higher initial costs when planning for future scenarios as a result of the additional water-energy nexus constraints taken into consideration. However, the performance of an integrated plan is shown to have several benefits during simulations of future scenarios including lower total costs, better resource efficiency and improved robustness in the face of various sources of uncertainty.