The missing measurement behind urban nature-based solutions resilience claims

Nature-based solutions (NbS) have become a central component of urban climate adaptation strategies, yet the indicators used to support resilience claims do not always reflect resilience as a system property. Many studies interpret short-term environmental improvements as evidence of resilience, although such indicators rarely capture the capacity of urban systems to withstand disturbances, adapt to changing conditions, and recover over time. This review applies an Output–Outcome–Impact–Resilience (OOIR) framework to a set of 97 urban NbS sources, identified through a structured, PRISMA-guided search of the Scopus and Web of Science databases, published between 2015 and 2025 to examine how resilience is operationalised in practice. Impact-level indicators were the most common, accounting for 53.6% of the sources, followed by outcome-level (26.8%) and output-level indicators (19.6%). Of the 97 sources reviewed, 62 (63.9%) explicitly claimed a contribution to resilience, yet 34 of these 62 (54.8%) supported that claim solely with impact-level indicators. Under the OOIR framework used in this study, none of the reviewed sources included indicators that met the criteria for direct resilience measurement. Governance-related sources accounted for the largest share of the set, whereas economic indicators remained rare. Outputs, outcomes, and impacts are frequently used as proxies for resilience, with implications for how NbS interventions are evaluated and monitored. To address this gap, the study proposes a resilience indicator framework covering ecological, social, economic, and governance dimensions, intended as a starting point for longitudinal monitoring and for improving the comparability of urban NbS assessments across sites and intervention types.