Advancing Nexus Approaches: insights from practice in support of their operationalisation

Sammanfattning: The last decade has seen the emergence of a new research theme - the study of the resources Nexus. The “Nexus” refers to considering the functioning of several systems simultaneously, as opposed to one, as the object of research. This perspective reasons that coherent decision-making needs to consider systems' interconnectedness. Typical system-of-systems (Nexus) studied relate to the security of services, such as the Water-Energy and Food Nexus, and resources, i.e. the Climate, Land, Energy and Water systems (CLEWs) Nexus. The process of examining cross-systems dynamics and interactions is known as the Nexus approach. Implementing it requires understanding multiple systems, disciplinary integration, and multi-stakeholder engagement at various decision levels. Adequate planning of an assessment process is needed to ensure the successful implementation of the approach and its long-lasting presence in decision-making processes. Therefore, reviewing the application of Nexus approaches can inform essential aspects that clarify and streamline the entire process. Current gaps in Nexus research include the lack of clarity in systems representation, the lack of flexible and accessible tools and methods for Nexus analyses, and the need for transparency in modelling approaches. All of these hinder the integration of the approach in research and the incorporation into decision-making processes. The thesis aims to advance the science of integrated resource assessments, particularly the Nexus approach, and support its dissemination and implementation within and beyond academia. Insights from applying two Nexus approaches (CLEWs and SIM4NEXUS) are distilled from the comparison of case studies. Overarching aspects examined include the expertise engaged in assessments, practitioners' roles and transdisciplinarity. Also analysed are selected components in the Nexus approach, such as identifying systems' interactions, analytical approaches, and stakeholder engagement and participation. The transversal feature of knowledge transfer between experts, practitioners, and stakeholders is examined to understand its importance in the assessment process. Examples of quantitative analyses illustrate the representation of different Nexus contexts and the elaboration of relevant insights. This thesis presents two such quantitative examples. One example is an entry-level CLEWs modelling exercise, whose development is described from conceptualisation, model development, and interpretation of results. The other example is a quantitative analysis of the transboundary Syr Darya river basin, which investigates the role of model structure in exploring Nexus questions. The thesis highlights a list of principles to support the Nexus approach's operationalisation deriving from practice and considering current research gaps.