[Paper Review] Urban greenery and mental wellbeing in adults: Cross-sectional mediation analyses on multiple pathways across different greenery measures

Ruoyu Wang, Marco Helbich+5 more|arXiv (Cornell University)|May 11, 2019

Urban Green Space and Health60 references19 citations

TL;DR

This study examines how urban greenery—measured via street-level imagery (streetscape greenery) and satellite-derived NDVI—affects adult mental wellbeing in Guangzhou, China, through multiple mediators including physical activity, stress, air quality, noise, and social cohesion. Streetscape greenery mediated 62% of its association with wellbeing via these pathways, while NDVI mediated only 22%, indicating distinct mechanisms for different greenery measures.

ABSTRACT

Multiple mechanisms have been proposed to explain how greenery enhances their mental wellbeing. Mediation studies, however, focus on a limited number of mechanisms and rely on remotely sensed greenery measures, which do not accurately capture how neighborhood greenery is perceived on the ground. To examine: 1) how streetscape and remote sensing-based greenery affect people's mental wellbeing in Guangzhou, China; 2) whether and, if so, to what extent the associations are mediated by physical activity, stress, air quality and noise, and social cohesion; and 3) whether differences in the mediation across the streetscape greenery and NDVI exposure metrics occurred. Mental wellbeing was quantified by the WHO-5 wellbeing index. Greenery measures were extracted at the neighborhood level: 1) streetscape greenery from street view data via a convolutional neural network, and 2) the NDVI remote sensing images. Single and multiple mediation analyses with multilevel regressions were conducted. Streetscape and NDVI greenery were weakly and positively, but not significantly, correlated. Our regression results revealed that streetscape greenery and NDVI were, individually and jointly, positively associated with mental wellbeing. Significant partial mediators for the streetscape greenery were physical activity, stress, air quality and noise, and social cohesion; together, they explained 62% of the association. For NDVI, only physical activity and social cohesion were significant partial mediators, accounting for 22% of the association. Mental health and wellbeing and both streetscape and satellite-derived greenery seem to be both directly correlated and indirectly mediated. Our findings signify that both greenery measures capture different aspects of natural environments and may contribute to people's wellbeing by means of different mechanisms.

Motivation & Objective

• To assess the impact of streetscape greenery and NDVI on adult mental wellbeing in Guangzhou, China.
• To identify and quantify the mediating pathways—physical activity, stress, air quality, noise, and social cohesion—linking greenery to mental wellbeing.
• To compare the relative contributions of streetscape greenery versus NDVI in explaining mental wellbeing through these mediators.
• To evaluate whether different greenery measures operate through distinct psychological and environmental mechanisms.
• To improve understanding of urban greenery's role in mental health by integrating ground-level and remote sensing data.

Proposed method

• Utilized street-level imagery from Google Street View, processed via a convolutional neural network (CNN) to quantify streetscape greenery at the neighborhood level.
• Extracted NDVI (Normalized Difference Vegetation Index) from satellite remote sensing data as a complementary measure of vegetation cover.
• Measured mental wellbeing using the WHO-5 Wellbeing Index, a validated self-report scale.
• Conducted single and multiple mediation analyses using multilevel regression models to account for neighborhood-level clustering.
• Tested the indirect effects of both greenery measures on wellbeing through each mediator, estimating total and specific indirect effects.
• Assessed model fit and significance using bootstrapped confidence intervals for indirect effects.

Experimental results

Research questions

• RQ1 How do streetscape greenery and NDVI independently relate to mental wellbeing in urban adults?
• RQ2 To what extent are the associations between greenery and mental wellbeing mediated by physical activity, stress, air quality, noise, and social cohesion?
• RQ3 How do the mediating pathways differ between streetscape greenery and NDVI?
• RQ4 What proportion of the greenery-wellbeing relationship is explained by the combined mediators for each greenery measure?
• RQ5 Do streetscape greenery and NDVI capture distinct aspects of urban nature that influence wellbeing through different mechanisms?

Key findings

• Streetscape greenery and NDVI showed a weak positive correlation but were not significantly correlated, indicating they measure different aspects of urban greenery.
• Streetscape greenery was significantly associated with higher mental wellbeing, with 62% of this association mediated by physical activity, stress, air quality, noise, and social cohesion.
• NDVI was also positively associated with mental wellbeing, but only 22% of this association was mediated by physical activity and social cohesion.
• Physical activity, stress, air quality, noise, and social cohesion were significant partial mediators for streetscape greenery, while only physical activity and social cohesion were significant for NDVI.
• The results suggest that streetscape greenery captures more nuanced, perceptually relevant environmental factors that influence mental wellbeing through multiple pathways.
• Both greenery measures contribute to wellbeing through direct and indirect pathways, but streetscape greenery explains a substantially larger proportion of the association via mediators.