Optimizing Urban Green Space for Cooling and Mental Well-Being in a Subtropical Megacity

Abstract

Subtropical cities face escalating heat stress and mental health challenges due to rapid urbanization and the urban heat island effect. However, how specific urban green space (UGS) configurations jointly shape microclimate and psychological well-being remains underexplored. We compared four UGS layouts in Shanghai: paved (no vegetation), grass-only, trees on pavement, and combined trees with grass. We monitored microclimatic parameters and thermal comfort (physiological equivalent temperature, PET), alongside standardized measures of psychological restoration and vitality. The trees + grass configuration produced the most favorable conditions, with lower daytime-averaged air and ground temperatures and the lowest mean PET compared with the paved control (mean PET: 30.44 vs. 39.48°C) and yielded the strongest psychological benefits (restoration +48.9%, vitality +40.5%). Tree canopies alone also provided significant cooling and mental health improvements. These findings suggest that multi-layer vegetation configurations, particularly trees + grass, can effectively maximize urban cooling and mental restoration, thereby supporting the design of climate-resilient urban green spaces.