19. Using Systems Thinking Approaches for ‘Nexus’ Understanding and Analysis

Human-natural systems are characterized by complex interactions across different domains, challenging sustainable resource management. Holistic approaches, such as the Nexus approach, are required to address mutual interdependencies across sectors and to explore synergies and trade-offs. This study applies a System Thinking approach, implemented through qualitative System Dynamics modelling based on Causal Loop Diagrams (CLDs), to identify and prioritize Nexus challenges, i.e., cross-sectoral issues that affect system sustainability. Structural and descriptive analyses of the CLDs are proposed to support this prioritization, while stakeholder engagement throughout the modelling process enhances system understanding. The modelling approach was applied to two Nexus hotspots: the Nima River Basin in Colombia, a Water-Ecosystem-Food (WEF) system facing water scarcity and pollution driven by intensive agriculture; and in the Ucayali Region in Peru, a Biodiversity-Climate-Society (BCS) system impacted by deforestation linked to cocoa production and weak infrastructure. Key findings highlight the central role of variables such as ‘water demand’ in Nima and ‘deforestation’ in Ucayali, which influence multiple sectors and therefore need attention. The approach revealed systemic trade-offs and sets the stage for identifying priority areas of the systems (i.e., leverage points) for integrated governance. The modelling process proves versatile, offering a robust, participatory framework applicable to diverse Nexus systems and contexts.