Population growth, urbanization and economic development drive the use of resources. Securing access to essential services such as energy, water, and food, while achieving sustainable development, require that policy and planning processes follow an integrated approach. The 'Climate-, Land-, Energy- and Water-systems' (CLEWs) framework assists the exploration of interactions between (and within) CLEW systems via quantitative means. The approach was first introduced by the International Atomic Energy Agency to conduct an integrated systems analysis of a biofuel chain. The framework assists the exploration of interactions between (and within) CLEW systems via quantitative means. Its multi-institutional application to the case of Mauritius in 2012 initiated the deployment of the framework. A vast number of completed and ongoing applications of CLEWs span different spatial and temporal scales, discussing two or more resource interactions under different political contexts. Also, the studies vary in purpose. This shapes the methods that support CLEWs-type analyses. In this paper, we detail the main steps of the CLEWs framework in perspective to its application over the years. We summarise and compare key applications, both published in the scientific literature, as working papers and reports by international organizations. We discuss differences in terms of geographic scope, purpose, interactions represented, analytical approach and stakeholder involvement. In addition, we review other assessments, which contributed to the advancement of the CLEWs framework. The paper delivers recommendations for the future development of the framework, as well as keys to success in this type of evaluations.

Over the past decades, the understanding and assessment of cross-systems interactions have gained momentum in research and policy support. As such, scientific literature on Nexus assessment methods and applications continues to grow, followed by numerous state-of-the-art reviews. Among the flexibility and variety of Nexus approaches, comprehensive, transferable and accessible methodologies with operational potential are missing. To address this gap, we introduce the SIM4NEXUS approach, which emerged from twelve test cases. Fledged from practice, the approach is a unique output in the Nexus research field. It is informed by the development of twelve case studies, which differ in spatial scope, socioeconomic and biophysical contexts, and Nexus challenges. The studies were conducted under similar conditions (e.g. timeframe and multidisciplinary teams of experts and dialogues with practitioners from policy and business). We find that transdisciplinarity and the integration of qualitative and quantitative methods are vital elements in Nexus assessments for policy support. Additionally, we also propose steps to advance Nexus assessments: (i) integration of the policy cycle in research (including monitoring and evaluation, and offer support during the implementation process), (ii) multidisciplinary collaboration with different levels of engagement and financial support, (iii) inclusion of ecosystems and other relevant dimensions (e.g. health) in the Nexus. Ultimately, the SIM4NEXUS approach provides practice-based guidance on conducting a Nexus assessment, and we recommend it for future Nexus assessments by the research community, institutions, and private actors.

A significant obstacle to the incorporation of Nexus considerations in planning and policy design is the understanding and acknowledgement of cross-sectoral interdependencies. This chapter explores the importance of disseminating knowledge of the Nexus among key actors from policy, business and civil society, and in formal education contexts. Examples from capacity development activities and Nexus dialogues linked to the implementation of the Climate, Land, Energy and Water systems (CLEWs) framework are presented. Insights from the latter, as well as other initiatives with similar scope of action, are distilled to forward the importance of learning in such an approach. Additionally, the chapter highlights the main aspects to take into account when promoting these types of activities in new Nexus contexts.

The Climate, Land, Energy and Water systems (CLEWs) approach guides the development of integrated assessments. The approach includes an analytical component that can be performed using simple accounting methods, soft-linking tools, incorporating cross-systems considerations in sectoral models, or using one modelling tool to represent CLEW systems. This paper describes how a CLEWs quantitative analysis can be performed using one single modelling tool, the Open Source Energy Modelling System (OSeMOSYS). Although OSeMOSYS was primarily developed for energy systems analysis, the tool’s functionality and flexibility allow for its application to CLEWs. A step-by-step explanation of how climate, land and water systems can be represented with OSeMOSYS, complemented with the interpretation of sets, parameters, and variables in the OSeMOSYS code, is provided. A hypothetical case serves as the basis for developing a modelling exercise that exemplifies the building of a CLEWs model in OSeMOSYS. System-centred scenario analysis is performed with the integrated model example to illustrate its application. The analysis of results shows how integrated insights can be derived from the quantitative exercise in the form of conflicts, trade-offs, opportunities, and synergies. In addition to the modelling exercise, using the OSeMOSYS-CLEWs example in teaching, training and open science is explored to support knowledge transfer and advancement in the field.

A motivation for integrated resource assessments is that they can capture indirect cross-sectoral effects of sectoral policies. This work investigates the electricity system implications from the implementation of basin-wide electricity and water systems efficiency measures. The spatial scope includes the four states that share the Syr Darya River basin. Different interests dictate the management of water resources in the basin. They are necessary for irrigation downstream in spring and summer and upstream, for hydropower generation during winter. The study investigated options to decrease the need for electricity upstream through efficiency measures and by the expansion of regional electricity trade. The scenarios were simulated by developing a multi-country electricity system model using the open source energy modelling system (OSeMOSYS). The results show that lesser investments in hydropower capacity could be needed and less water required in winter. This would reduce pressure on shared water resources.