Nature-Based Solutions (NBS) are becoming a widely funded alternative to grey infrastructure for flood mitigation, and can provide multiple co-benefits, but research literature identifies many barriers and challenges to their adoption. This study aims to inform decision-making regarding NBS suitability for flood mitigation through three research questions: 1) Does scientific literature of worldwide case-studies show that NBS mitigate fluvial floods?, 2) Do NBS case-studies provide all the ecosystem services/co-benefits that make them such a popular mitigative strategy for flood events?, and 3) Are NBS governance policies, frameworks, and flood risk analyses taking into account at-risk communities and do NBS case-studies include environmental justice for communities? The systematic review identifies 131 peer-reviewed papers worldwide, with case-studies related to NBS fluvial flood mitigation, co-benefits, and environmental justice policies and frameworks. A further meta-analysis of the literature is included to quantitatively evaluate flood mitigative potential and quantified co-benefits. While our research demonstrates that NBS are clearly able to mitigate fluvial floods, inconsistencies in measurement methods, few empirical case-studies, and large ranges in reported values impede comparison across NBS. There is a clear and urgent need for developing and implementing design and performance standards for large-scale NBS, and for guidance on which measures are important to report for flood mitigation and co-benefits. The success of large-scale NBS for fluvial flood mitigation will depend on transdisciplinary research that employs systems thinking and stakeholder co-design to implement NBS within watershed and local contexts, and to develop new integrative concepts with communication and data-sharing for broader applicability.
