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 assess-ments. 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 pri-marily 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, energy, 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.

Water, energy, and food are all essential components of human societies. Collectively, their respective resource systems are interconnected in what is called the "nexus". There is growing consensus that a holistic understanding of the interdependencies and trade-offs between these sectors and other related systems is critical to solving many of the global challenges they present. While nexus research has grown exponentially since 2011, there is no unified, overarching approach, and the implementation of concepts remains hampered by the lack of clear case studies. Here, we present the results of a collaborative thought exercise involving 75 scientists and summarize them into 10 key recommendations covering: the most critical nexus issues of today, emerging themes, and where future efforts should be directed. We conclude that a nexus community of practice to promote open communication among researchers, to maintain and share standardized datasets, and to develop applied case studies will facilitate transparent comparisons of models and encourage the adoption of nexus approaches in practice.

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: 1) integration of the policy cycle in research (including monitoring and evaluation, and offer support during the implementation process), 2) multidisciplinary collaboration with different levels of engagement and financial support, 3) 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.

Energy system modeling can be used to develop internally consistent quantified scenarios. These provide key insights needed to mobilise finance, understand market development, infrastructure deployment and the associated role of institutions, and generally support improved policymaking. However, access to data is often a barrier to starting energy system modeling, especially in developing countries, thereby causing delays to decision making. Therefore, this article provides data that can be used to create a simple zero-order energy system model for a range of developing countries in Africa, East Asia, and South America, which can act as a starting point for further model development and scenario analysis. The data are collected entirely from publicly available and accessible sources, including the websites and databases of international organisations, journal articles, and existing modeling studies. This means that the datasets can be easily updated based on the latest available information or more detailed and accurate local data. As an example, these data were also used to calibrate a simple energy system model for Kenya using the Open Source Energy Modeling System (OSeMOSYS) and three stylized scenarios (Fossil Future, Least Cost and Net Zero by 2050) for 2020-2050. The assumptions used and the results of these scenarios are presented in the appendix as an illustrative example of what can be done with these data. This simple model can be adapted and further developed by in-country analysts and academics, providing a platform for future work.

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.

Paraguay's power system is based entirely on hydropower. It serves as the largest net electricity exporter in Latin America. Nonetheless, the country´s electricity consumption per capita is one of the lowest in the world and the transmission and distribution network has one of the highest losses in Latin America. This paper presents an electricity expansion investment outlook (2018–2040) for Paraguay using OSeMOSYS, analyzing three electricity demand scenarios under different electricity export prices to Brazil. The study identifies the least-cost power generation mix, future investments and the financial requirements to meet the needs of different demand scenarios. We find that Paraguay will need to invest in hydropower plants, by mainly expanding the capacity of Yacyreta to cover its electricity needs and sustain national electricity exports levels. In the High demand scenario, where the electricity demand could approximately double by 2040, the country's overall electricity exports decrease by 50% compared to the Reference scenario. Based on the different scenarios examined, the government spends approximately 18.3–31.2 billion USD on power plant investments for the period 2018–2040 to cover future electricity demand. The findings could be useful in supporting decision-making concerning socio-economic development pathways in the country.

Integrated Assessment Models (IAMs) are important tools to analyse cross-sectoral interdependencies and the use of global resources. Most current tools are highly detailed and require expert knowledge and proprietary software to generate scenarios and analyse their insights. In this paper, the complementary Global Least-cost User-friendly CLEWs Open-Source Exploratory (GLUCOSE) model is presented as a highly-aggregated global IAM, open and accessible from source to solver and using the OSeMOSYS tool and the CLEWs framework. The model enables the exploration of policy measures on the future development of the integrated resource system. Thanks to its relatively simple structure, it requires low computational resources allowing for the generation of a large number of scenarios or to quickly conduct preliminary investigations. GLUCOSE is targeted towards education and training purposes by a range of interested parties, from students to stakeholders and decision-makers, to explore possible future pathways towards the sustainable management of global resources.

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.

Compliance with the Paris Agreement requires the transformation of national economies to meet net-zero carbon dioxide emissions by mid-century. To accomplish this, countries need to define long-term decarbonisation strategies with near- and mid-term actions to determine their ideal future scenario while maximizing socioeconomic benefits. This paper describes the process followed to support the creation of the decarbonisation pathway for the transport and energy sectors presented in Costa Rica's National Decarbonisation Plan. We discuss in detail the technological pathway of a deep-decarbonisation future that supports reaching net-zero emissions by 2050. Compared to a business-as-usual (BAU) scenario, our results show that the decarbonisation pathway can lead to emissions' reduction of 87% in the transport and energy sectors by 2050. Energy efficiency, the adoption of electromobility, modal-shift towards public transport and active mobility, as well as reduced demand due to digitalisation and teleworking, are found to be key drivers towards the deep-decarbonisation. These measures combined enable a 25% reduction of primary energy production by 2050. The results highlight that the decarbonisation scenario requires installing 4.4 GW more of renewable power plants by 2050, compared to the BAU scenario (80%). We also show that additional investments for the deep-decarbonisation are compensated with the reduced operating cost. Crucially, we found that the National Decarbonisation Plan results in a lower total discounted cost of about 35% of current Costa Rica's GDP, indicating that a deep decarbonisation is technically feasible and is coupled to socioeconomic benefits.