A Water-Energy-Food-Ecosystems nexus coherence assessment of solutions in the Danube River Basin

Climate change and socio-economic development are intensifying pressure on natural resources in the Danube River Basin, leading to more frequent droughts and water scarcity, and threatening both ecosystem conservation and economic activities. The Water-Energy-Food-Ecosystems (WEFE) nexus approach analyses interconnections between sectors to enhance resource efficiency. To address these challenges, this study conducted a nexus coherence assessment of two water-related solutions: increasing ecological flows and expanding wastewater reuse for agricultural irrigation. A participatory process was applied to co-design and evaluate these measures, involving around 158 stakeholders across dialogues and workshops, complemented by expert consultation. Additionally, Nexus Cross-Impact Analysis (N-CIA), a quantitative analytical tool grounded in network theory was used to assess cross-sectoral synergies and trade-offs. Evaluation results indicate that increasing ecological flows creates synergies for aquatic ecosystems but entails trade-offs in terms of reduced hydropower generation and increased greenhouse gas emissions. In contrast, expanding wastewater reuse creates synergies with agricultural production and socio-economic development, although it may also involve trade-offs for aquatic ecosystems. When considered jointly, the two solutions show potential to balance trade-offs while addressing water scarcity. The study highlights the importance of quantitatively assessing impacts across sectors to move beyond intuition and ensure coherent policy evaluation. It also demonstrates how stakeholder participation and expert input can enhance the design and assessment of solutions. The applied framework reveals hidden dynamics and leverage points within the nexus, providing a stronger basis for integrated resource management. Beyond technical results, the study fostered dialogue among diverse actors, supporting sustainability in the Danube.