Samenvatting

Urbanisation and climate change increase the need for quantitative insight into the contribution of nature-based solutions (NbS) to climate adaptation. While NbS are widely implemented at local scales, their aggregated contribution to regional and national adaptation ambitions remains largely unknown. This study addresses this gap by quantifying the type, amount and water storage capacity of NbS using the open-source ClimateScan platform, with relevance for municipalities and water authorities. The analysis uses a global dataset of over 21,000 climate adaptation projects collected through the citizen science platform ClimateScan.org. Projects are categorised (e.g. green roofs, bioswales, permeable pavements) and georeferenced. Water storage volumes were estimated using surface areas derived from mapped polygons, excluding areas >10,000 m². For point-based entries, average surface values per category were applied. Depths were conservatively assigned based on standard guidelines. Results show that NbS in the Netherlands have created at least 1,604,840 m³ of water storage capacity over the past 20 years. Larger cities show high total volumes and numbers of measures, while smaller municipalities often perform higher relative to population. These results provide first-order insights into the contribution of NbS at national scale. The study concludes that ClimateScan enables initial quantification of NbS and supports knowledge exchange on climate adaptation. To improve accuracy and usability for decision-making, further development is needed, including increased use of polygon mapping, validation by expert users, and verification with municipalities and water authorities.