Nature-based solutions are crucial for addressing urban environmental challenges by enhancing climate resilience, improving biodiversity, and promoting mental well-being. However, their effective implementation requires a Nexus-driven, integrated approach that bridges ecological, social, and governance dimensions. The Urban ReLeaf project exemplifies this paradigm by fostering citizen science as a process for cross-sectoral collaboration, ensuring that data-driven greenspace policies align with broader sustainability objectives.

In six European cities - Athens, Cascais, Dundee, Mannheim, Riga, and Utrecht - citizen science plays a pivotal role in resource management by generating critical, multi-dimensional datasets that inform policy interventions. Athens is advancing participatory urban greening through a community-supported tree registry, strengthening urban ecosystem governance. Through map-based surveys Cascais incorporates citizen-reported perceptions into climate-responsive greenspace planning, while Dundee co-develops strategies with socially vulnerable communities gathering perceptions of greenspace and nature whilst exploring far-future 'what if...' scenarios.’ Mannheim integrates citizen-collected data on urban tree conditions into greenspace management, ensuring evidence-based decision-making. In Riga, collaborative air pollution monitoring fosters interdisciplinary insights into the air quality and urban greenspace relationship, supporting urban resilience strategies. Utrecht mobilizes local groups to assess microclimatic variables using wearable sensors in green-deprived neighborhoods, reinforcing the need for data-driven mitigation strategies in climate adaptation.

Urban ReLeaf illustrates how citizen science, data-informed policy innovation, and integrated urban planning can break down sectoral silos and drive sustainable resource management. The presentation will highlight the transformative potential of citizen science in operationalizing the Nexus approach, fostering collaborative governance and ensuring that urban ecosystems serve both environmental and societal needs.