Assessing the impacts of nature-based solutions is essential to understand their effectiveness in addressing current interrelated societal challenges. Robust impact evaluation supports practitioners to understand and document the outcomes of nature-based solutions, resulting in improved quality, efficiency and effectiveness at various stages of nature-based solution implementation. Knowing which nature-based interventions are effective and at what cost is critical for decisions about the action itself, as well as for assessment of the up-scaling and/or replication potential of a given nature-based solution. This publication provides a summary of key principles in developing your impact evaluation framework, which includes the development of your theory of change, and the selection of appropriate indicators of impact and methods to obtain useful and high-quality data. Through the presentation of four European nature-based solution case studies, with diverse geographies and challenges, we illustrate how impact evaluation can be tailored to local contexts. We hope to inspire you to further explore the detailed information available in Evaluating the Impact of Nature-Based Solutions: A Handbook for Practitioners, and the accompanying Evaluating the Impact of Nature-Based Solutions: Appendix of Methods.

The Handbook aims to provide decision-makers with a comprehensive NBS impact assessment framework, and a robust set of indicators and methodologies to assess impacts of nature-based solutions across 12 societal challenge areas: Climate Resilience; Water Management; Natural and Climate Hazards; Green Space Management; Biodiversity; Air Quality; Place Regeneration; Knowledge and Social Capacity Building for Sustainable Urban Transformation; Participatory Planning and Governance; Social Justice and Social Cohesion; Health and Well-being; New Economic Opportunities and Green Jobs. Indicators have been developed collaboratively by representatives of 17 individual EU-funded NBS projects and collaborating institutions such as the EEA and JRC, as part of the European Taskforce for NBS Impact Assessment, with the four-fold objective of: serving as a reference for relevant EU policies and activities; orient urban practitioners in developing robust impact evaluation frameworks for nature-based solutions at different scales; expand upon the pioneering work of the EKLIPSE framework by providing a comprehensive set of indicators and methodologies; and build the European evidence base regarding NBS impacts. They reflect the state of the art in current scientific research on impacts of nature-based solutions and valid and standardized methods of assessment, as well as the state of play in urban implementation of evaluation frameworks.