Neighbourhood greenness and mental well-being: A spatial-scale analysis in two German cities, 2024

Abstract Increasing urbanization poses significant challenges to the mental health of urban populations. Urban green spaces are known to support mental well-being by reducing stress, promoting physical activity, and fostering social interaction. However, empirical evidence on the relationship between green infrastructure and mental health remains inconsistent, partly due to methodological differences, study area characteristics and spatial scales. In selected districts of two German cities, a random sample was drawn from the local population registers, with 2,157 residents providing georeferenced residential data for the analysis. The association between greenness, measured by the Normalized Difference Vegetation Index (NDVI), and mental wellbeing, assessed using the WHO-5 Well-Being Index (WHO-5), was examined at neighbourhood level across different spatial scales. Sociodemographic factors such as gender, age, and monthly net household income were included. The mean WHO-5 score in the sample was 14.52 (SD: 4.78). NDVI values typically ranged from around 0.17 at small scales (10-25 m) to around 0.28 at larger scales (700-1,000 m). A significant association was found between NDVI and WHO-5 at small spatial scales (β = 2.97 at 10 m; β = 2.42 at 25 m) and again at larger scales (β = 2.18 at 700 m; β = 3.26 at 1,000 m), but no significant associations were observed at intermediate spatial scales (50-600 meters), with coefficients ranging from 0.30 to 1.72 and no consistent pattern. This suggests a U-shaped relationship between spatial scale and effect strength. The results indicate that while the NDVI and sociodemographic data provides valuable insights, they do not fully capture the complexity of human-environment interactions. Future studies should consider incorporating qualitative data, such as individual experiences and perceptions of green space quality, to deepen the understanding of the relationship between green infrastructure and mental health. Key messages • Mental well-being is linked to greenness at very small and large spatial scales, showing a U-shaped relationship. • Combining NDVI with additional variables provides a more comprehensive understanding of the impact of green spaces on mental well-being.