Revisiting the role of the Nature-based Solutions Standards to promote climate adaptation in cities

• Implementing NbS criteria can be essential to ensure its full potential. • Studies are still focused on NbS biophysical dimension. • Increased complexity in NbS projects can reduce effect size but increase its variability. • Social, economic, and political dimensions need greater consideration in NbS research. • Interdisciplinary collaboration can be crucial for advancing NbS projects implementation. Nature-based Solutions (NbS) are increasingly recognized as key strategies for urban climate adaptation. To ensure effectiveness and avoid conceptual dilution, the International Union for Conservation of Nature (IUCN) established a Global Standard comprising eight guiding criteria. However, the extent to which these criteria are incorporated into scientific research remains unclear. Here, we conduct a meta-analysis of 79 peer-reviewed studies to evaluate how the IUCN criteria are applied in NbS literature focused on cities, and whether their inclusion relates to reported adaptation outcomes. Our results show that most studies emphasize biophysical aspects, such as temperature or runoff reduction, while largely overlooking social, institutional, and temporal dimensions. Criteria such as Governance, Trade-offs, and Adaptive management appear in less than 10% of the studies. We also find a negative association between the number of criteria considered and the mean effect size, with greater variability in outcomes as complexity increases. These findings suggest that while multidimensional integration is essential, it also poses implementation challenges. Bridging these gaps will require adaptive approaches that align ecological performance with governance, long-term monitoring, and social needs. Advancing NbS research through more comprehensive and standardized assessments is critical to ensure their credibility, equity, and long-term relevance in urban climate adaptation.