We developed and examined a set of indicators, called the UNI, intended to measure urban ecological performance while meeting diverse cities’ needs and monitoring capacities. Our findings suggest that because users can select indicators within each theme and since the number of indicators selected is based on the city’s capacity level, the proposed UNI provides flexibility that can meet the needs of cities piloted across IUCN regions and income levels. Additionally, the UNI’s Capacity Assessment Questionnaire guides local level users in selecting appropriate and feasible indicators for their context. The UNI was developed by experts from several areas of expertise working across multiple scales, and due to it being structured in line with international ecological measuring criteria and goal setting approaches, the tool has the potential to raise ambition at the local level, prompting action toward achieving biodiversity targets at the global level.
Key to cities implementing global and national biodiversity goals are effective monitoring and science-based target setting, contingent with metrics that show progress in relative and absolute terms. Although several sets of indicators exist to monitor urban biodiversity, most are rigid and inadequately reflect the complexity inherent in cities, as well as the multiple scales at which impacts of biodiversity loss are felt by cities 30,31. Further, no internationally agreed upon approach to measuring biodiversity at the local level exists; hindering the successful implementation of biodiversity conservation plans 15,14. In response to this lack of standardized indicators to measure the impact that cities have on nature, we compiled the UNI, consisting of a comprehensive set of 30 indicator topics nested across six themes. Further, the indicators were generated using a deductive conceptual framework focusing on measurable impacts. Therefore, the UNI can guide cities in achieving biodiversity and nature restoration goals within and beyond their boundaries.The intention for the UNI is to be flexible yet standardised such that a wide array of cities can complete urban nature assessments in a roughly comparable way within each thematic category. It is also meant to be sufficiently robust to provide a meaningful measure while also being feasible enough for cities with a range of capacities to update every 1 to 5 years. We found that while city representatives mention the SDGs or other nationally determined standards as guiding monitoring efforts, no international standard for monitoring nature and biodiversity in cities was being followed consistently. Among the selected cities, most report monitoring some or several features of, or impacts on, nature, yet how they measure and prioritize them differs vastly.
Cities lack guidelines that would ensure that their ecological impacts are being considered across multiple scales, from local to global. Furthermore, priorities among cities differ significantly enough to hinder comparability across locations and aggregation of impacts of local action at larger scales. However, some more straightforward and quantifiable topics such as pollution and waste were more commonly measured. This may in part be attributable to concerted efforts in the 1990s to early 2000s and the need for cities to measure and report on material flows and progress toward achieving the Millennium Development Goals, predecessor to the SDGs, with explicit focus on gauging economic growth and efforts to improve public health 32. These types of straightforward measures differ from indicators that attempt to capture the interconnected well-being of ecological systems and humans 33. Addressing socio-ecological systems as a whole also responds to the call to improve global monitoring of human development, central to the SDGs 20,34.
We find that nearly half of cities surveyed used the SDGs to guide monitoring efforts, although the 17 SDGs, which are accompanied by 169 targets and roughly 250 indicators, are designed to measure progress toward sustainability, and not ecological performance. Less commonly, piloted participant cities followed nationally determined standards, or non-binding national plans or policies mostly focused on climate change mitigation, including but not limited to climate-related targets to measure reductions in greenhouse gas emissions 35.
Although climate change, biodiversity decline, unsustainable land use and inequitable natural resource extraction are tightly interlinked and cumulatively degrade human well-being 36, their associated targets and indicators are not interchangeable and cannot be used as proxies to infer ecological performance. Anthropogenic climate change, biodiversity decline37, land degradation38, and natural resource exploitation39 directly impact ecosystem stability and the benefits society receives from nature40. These impacts vary in their nature and occur across different timescales.
The uneven distribution of benefits resulting from natural resource extraction and use often leads to social and economic disparities, which indirectly drives biodiversity loss. The synergistic effects of these factors on ecological performance pose a significant risk to human well-being. Therefore, targets and indicators that amalgamate measures across these drivers may provide misleading reports on urban ecological performance.
Further, nationally determined standards are, as implied by their name, typically measured and reported at the country-level. As a result, they rarely offer local-level monitoring guidance or opportunities for cross-comparison opportunities 41,42.
One local-level tool currently in use is the Singapore Index for Cities' Biodiversity (SICB), which provides a broad range of indicators but has limitations concerning its application and coverage 43. Unlike UNI, the SICB focuses solely on impacts within city boundaries and lacks institutional support for global application. The development of the UNI addresses this gap by recognizing and emphasizing the broader ecological footprint of cities, encompassing both local and global scales 44. The key novelty of the UNI is its application of the urban bioshed model that underscores the telecoupled impacts of cities beyond their physical boundaries. The inclusion of urban, city-bioregional, and global scales within a comprehensive framework acknowledges the complexities of urban-ecological systems and provides a path for cities to participate in sustainable environmental action effectively.
Despite the interest and engagement in urban ecological well-being, the study shows that a lack of resources and technical expertise remains the most common obstacle hindering effective monitoring efforts. This discrepancy highlights the necessity for a tool like the UNI, which is designed to be robust yet feasible for cities with various capacities. For cities, especially those classified as low- to lower-income, the use of the UNI can provide numerous benefits, including facilitating the establishment of larger-scale programs that direct support and funding to the local level. This, in turn, may elevate the priority given to nature and biodiversity conservation in city governance, as well as assist local governments in forming and implementing their conservation strategies. By incorporating telecoupling - the ecological impacts of cities beyond their local footprint - the UNI provides an innovative approach to track urban nature in a way that is adaptable to specific city contexts and resources. This innovative index offers cities an effective mechanism to contribute to national, regional, and global monitoring efforts, thereby enhancing transparency and accountability in environmental monitoring and promoting local action for nature.
The UNI, backed by institutional support from the IUCN, presents a cost-effective solution to overcome the limitations faced by cities in tracking their impact on biodiversity and environmental sustainability. It provides a common standard and a methodologically rigorous yet adaptable tool for cities to evaluate their ecological health and to inform their biodiversity policy development. In contrast to many existing tools, the UNI takes into account the crossboundary impacts of urban environments and the multi-scalar nature of ecological phenomena, offering a more holistic approach to urban nature monitoring. Beyond the immediate benefits of a more robust monitoring system, the UNI also fosters a global community of cities working collaboratively towards shared ecological objectives. This international network can serve as a platform for knowledge sharing, capacity building, and mutual support, reinforcing global commitments to urban nature conservation. The provision of an online platform by IUCN for practitioners with diverse knowledge and skill sets furthers this collaborative potential, providing a virtual space for the exchange of best practices and the co-creation of innovative solutions. Furthermore, the UNI can also play a pivotal role in mobilizing resources and galvanizing political support for urban biodiversity conservation. By demonstrating the feasibility and importance of tracking ecological health, the UNI can stimulate increased investment in monitoring infrastructure, the training of local environmental professionals, and the development of science-based policies and interventions. For low- to lower-income cities, the UNI can also help attract international funding and technical assistance, thereby mitigating the resource constraints that often impede effective environmental governance.
A further strength of the UNI, which is an IUCN knowledge product, is that it will be supported by IUCN in terms of application, monitoring, consistency, and evolution over time. IUCN will also ensure the management and coordination of the UNI web-platform in the long-term and support municipalities in the implementation of the Indexes as part of its activities.
As a standardized framework for urban ecological impacts such as the UNI becomes established, operationalizing targets at a subglobal (regional/local) and global scale is then critical to improve conservation approaches that will shape the next 30 years 45. Consistent guidance for comprehensive targets that link local ecological performance and global impacts have yet to take hold, though targets have been proposed for particular topics such as greenhouse gas emissions, canopy coverage, or access to green spaces. Rockstrom et al.46 recently proposed a set of targets called Earth System Boundaries to ensure a stable, resilient, biophysical condition to sustain the “global commons” and which also include locally-relevant target-setting. The UNI is in a good position to link its framework to targets such as particular Earth System Boundaries, or those set by local or national governments. The ability to compare performance of cities within widely differing contexts is one of the benefits of a consistent global standard for local actions.
In conclusion, the UNI has the potential to catalyze a paradigm shift in how cities understand and respond to their environmental footprints, making visible the complex interconnections between urban activities and global biodiversity. By contributing to the emergence of a more ecologically-informed urban planning and management, the UNI can transform cities from sources of environmental pressures to leaders in nature-positive transformations. As the UNI continues to evolve, it will increasingly shape urban nature conservation practices and policies worldwide, responding to advancements in monitoring techniques and user feedback. It represents a promising tool that substantially enhances cities' capacity to monitor, understand, and improve their ecological performance, while also laying the groundwork for a more sustainable and inclusive urban future.