Cross-scale collaborative planning approach for sustainable water management: A blue-green infrastructure vision for the Huangyan–Taizhou Region, China

Accelerating urbanization and growing water demand make cross-scale approaches to sustainable water management imperative across hydrologically connected urban regions. Integrated Water Resources Management (IWRM) has long emphasized coordinated, multi-scale governance linking upstream–downstream allocation, basin-scale management, stakeholder participation, and institutional coordination. Yet translating these principles into spatially explicit, community-supported planning actions remains challenging. Blue–green infrastructure (BGI) can serve as a practical, place-based instrument for this translation, but existing BGI research remains fragmented by scale, limiting coordination between regional strategies and local implementation, especially in rapidly urbanizing and institutionally complex contexts. In response, this study develops a cross-scale collaborative planning approach integrating multi-level mapping and stakeholder engagement for BGI planning. Conducted within the six-year Sino–German Urban–Rural Assembly project (2019–2024), it is applied in the rapidly urbanizing Huangyan–Taizhou Region, China, where inequitable water allocation, pollution, ecosystem degradation, and shifting sociocultural water dynamics pose major challenges. We investigate: (1) How can cross-scale mapping translate regional water concerns into localized BGI actions? (2) What governance mechanisms enable map-based analysis to support coordinated multi-stakeholder planning? (3) How can cross-scale collaborative BGI planning be embedded in top-down local governance while enabling bottom-up participation and cross-departmental coordination? The approach integrates regional visioning through expert workshops, transect-scale co-mapping of agricultural and industrial transition zones, and site-level co-design refined via workshops and interviews. Findings show that cross-scale mapping strengthens regional-to-site linkages, while collaborative planning translates analysis into stakeholder-supported interventions across scales and institutions. The study delivers actionable BGI strategies for Huangyan–Taizhou and a transferable framework for similar regions.