Quantifying the Spatio-Ecological Context of Urban Nature-Based Solutions Across European Cities

Nature-Based Solutions (NBS) are increasingly implemented to address urban environmental challenges, yet the surrounding spatial context in which they are embedded may influence the conditions supporting their ecological functioning. This study applied an integrated remote sensing-based spatial diagnostic framework combining Sentinel-2 spectral indices and land-cover composition metrics to characterize and compare the surrounding environments of five NBS sites in Oslo, Riga, Milan, St. Gallen, and Lublin. The Normalized Difference Vegetation Index (NDVI), Normalized Difference Moisture Index (NDMI), and Normalized Difference Built-Up Index (NDBI) were analyzed within 100 m, 300 m, and 500 m buffer zones alongside land-cover composition assessments. The analysis revealed substantial variation in vegetation greenness, moisture conditions, built-up intensity, and landscape composition. Three spatial-context profiles were identified: low-density/peri-urban settings, exemplified by the Riga NBS site with consistently high NDVI (0.483–0.374), positive NDMI (0.230–0.171), and strongly negative NDBI (−0.230 to −0.171); mixed urban settings, represented by the Oslo, Lublin, and St. Gallen NBS sites; and dense urban settings, represented by the Milan NBS site, which exhibited the lowest NDVI (0.197–0.124), declining NDMI (0.054 to −0.014), and positive NDBI beyond 300 m (0.001–0.014). These findings demonstrate that surrounding landscape characteristics provide a meaningful basis for distinguishing urban NBS settings. The proposed replicable framework can support context-sensitive planning by identifying areas where complementary landscape-scale measures, including de-paving, strategic greening, and improved landscape connectivity, may be considered to strengthen the broader environmental conditions surrounding NBS.