Search

International audience; In the context of climate change, Nature-Based Solutions (NBSs), a recently developed concept, are increasingly considered as part of the adaptation strategies of the cities. Studies using expert models and methods (EMM) receive a great deal of scientific attention. Considering EMM increasing use, this study aims to perform an analysis of the reported evaluation results, reflecting the capability of the EMM to accurately tackle urban challenges identified within the EU Nature4Cities project. Then, we propose a set of indicators and recommendations about sixteen EMM to be used by funders, researchers and practitioners when evaluating the performance of NBSs. The coupling of the different components (climate, water and soil) is not a simple matter. The analysis relies on the definition of the range of the reported metrics and on the investigation of the relationship between the various indices, applied for the EMM evaluation. Secondly, the study assesses the existing EMM, indicating the potential of NBSs: (i) to reduce urban heat island, (ii) to limit surface warming, (iii) to increase the thermal comfort of people, (iv) to limit the overheating and runoff of surfaces due to impervious areas, (v) to increase water retention during stormy episodes, (vi) to improve storm water quality at the outlet of the sustainable urban drainage systems, (vii) to promote the filtration and epuration of storm water runoff in soil and (viii) to be a support for vegetation. The analysis reveals that EMM can be considered as helpful tools for urban microclimate, urban soil and water management analysis, provided their limitations and characteristics are taken into account by the user when choosing tools and interpreting results (e.g. application scale). With regard to the performance of NBSs, the most commonly used indicators clearly depend on the scale of the project.

The UN System of Environmental-Economic Accounting Ecosystem Accounting (SEEA EA) aims at regular and standardised stocktaking of the extent of ecosystems, their condition, and the services they provide to society. Recording the condition of ecosystems is one of the most complex pieces in this exercise and needs to be supported by consistent guidelines. SEEA EA defines the condition of an ecosystem as its overall quality, measured in terms of quantitative metrics describing its abiotic and biotic characteristics. One of the key challenges lies in identifying the most appropriate metrics for each ecosystem type that capture these essential characteristics. The objective of this paper is to create a well-defined framework for transparent and operative development of ecosystem condition indicators, which can be used in ecosystem accounting and ecosystem assessment studies. Starting from the SEEA EA documentation and a small targeted systematic review, we identified 12 key criteria, which we grouped according to their roles during the indicator development process. Five conceptual criteria (intrinsic relevance, instrumental relevance, sensitivity, directional meaning, and framework conformity) outline the priorities for identifying relevant characteristics of the ecosystems. Five practical criteria (validity, reliability, availability, simplicity, and compatibility) provide guidance on identifying concrete quantitative metrics for the selected characteristics. Finally, two ensemble criteria (comprehensiveness, and parsimony) ensure the completeness and complementarity of the final set of metrics. To tackle the climate and biodiversity crises, the condition of ecosystems needs to be better recognized in national economic planning. The proposed framework supports the selection of a concise set of salient and credible ecosystem condition indicators through a transparent, repeatable and scientific process. This can make the compilation of ecosystem condition accounts more accessible and more standardised on a global level, which is a key prerequisite for the success of SEEA EA. Additionally, the framework presented in this paper may be useful in other contexts where ecological, environmental, or sustainability indicators need to be identified.