Optimizing urban green spaces to enhance cooling intensity and heat resistance across thermal comfort gradients

Enhancing the cooling intensity (CI) and heat resistance (HR) of urban green spaces (UGS) is crucial for improving urban thermal comfort. However, the cooling effect of these UGS is usually evaluated under a single temperature condition, which may overlook whether the cooling effect remains effective and stable when heat stress intensifies. This study utilized long-term land surface temperature, meteorological, and UGS data from Xi'an, China, to quantify CI and HR across six thermal comfort levels, and to investigate their relationships with area and NDVI. The results showed that NDVI was more strongly associated with CI, whereas area was relatively more important for HR, suggesting that interventions aimed at stronger cooling may not deliver equivalent improvements in thermal stability. As background thermal stress increased from comfortable to extreme heat conditions, CI of green spaces increased continuously, while HR exhibited a non-linear response, showing that greater CI does not necessarily imply greater stability. NDVI and area exhibited diminishing returns, indicating that maximizing area and NDVI alone is insufficient to optimize thermal performance Improved vegetation quality could partly compensate for limited area, but this substitution became progressively less efficient as cooling targets increased. These findings support a shift from maximizing green-space quantity toward coordinating area and vegetation quality according to CI and HR. For cities facing land constraints, improving existing vegetation offers a means of strengthening cooling services, while retaining sufficient green-space area remains important for thermal stability under increasing heat stress.