Department of Urban Planning and Design, Xi'an Jiaotong-Liverpool University, Suzhou, China.
Department of Public Health, Environment and Society, London School of Hygiene and Tropical Medicine, London, UK.
Environ Health Perspect. 2023 Sep;131(9):97007. doi: 10.1289/EHP12589. Epub 2023 Sep 20.
The protective effect of urban greenery from adverse heat impacts remains inconclusive. Existing inconsistent findings could be attributed to the different estimation techniques used.
We investigated how effect modifications of urban greenery on heat-mortality associations vary when using different greenery measurements reflecting overhead-view and eye-level urban greenery.
We collected meteorological and daily mortality data for 286 territory planning units between 2005 and 2018 in Hong Kong. Three greenery measurements were extracted for each unit: ) the normalized difference vegetation index (NDVI) from Landsat remote sensing images, ) the percentage of greenspace based on land use data, and ) eye-level street greenery from street view images via a deep learning technique. Time-series analyses were performed using the case time series design with a linear interaction between the temperature term and each of the three greenery measurements. Effect modifications were also estimated for different age groups, sex categories, and cause-specific diseases.
Higher mortality risks were associated with both moderate and extreme heat, with relative risks (RRs) of 1.022 (95% CI: 1.000, 1.044) and 1.045 (95% CI: 1.013, 1.079) at the 90th and 99th percentiles of temperatures relative to the minimum mortality temperature (MMT). Lower RRs were observed in greener areas whichever of the three greenery measurements was used, but the disparity of RRs between areas with low and high levels of urban greenery was more apparent when using eye-level street greenery as the index at high temperatures (99th percentile relative to MMT), with RRs for low and high levels of greenery, respectively, of 1.096 (95% CI: 1.035, 1.161) and 0.985 (95% CI: 0.920, 1.055) for NDVI (), 1.068 (95% CI: 1.021, 1.117) and 0.990 (95% CI: 0.906, 1.081) for the percentage of greenspace (), and 1.103 (95% CI: 1.034, 1.177) and 0.943 (95% CI: 0.841, 1.057) for eye-level street greenery (). Health discrepancies remained for nonaccidental mortality and cardiorespiratory diseases and were more apparent for older adults ( years of age) and females.
This study provides new evidence that eye-level street greenery shows stronger associations with reduced heat-mortality risks compared with overhead-view greenery based on NDVI and percentage of greenspace. The effect modification of urban greenery tends to be amplified as temperatures rise and are more apparent in older adults and females. Heat mitigation strategies and health interventions, in particular with regard to accessible and visible greenery, are needed for helping heat-sensitive subpopulation groups in coping with extreme heat. https://doi.org/10.1289/EHP12589.
城市绿化对不利热影响的保护作用仍不确定。现有不一致的研究结果可能归因于使用的不同估计技术。
我们研究了在使用反映头顶视角和眼平面城市绿化的不同绿化测量值时，城市绿化对热死亡率关联的影响修饰如何变化。
我们收集了 2005 年至 2018 年香港 286 个领土规划单元的气象和每日死亡率数据。为每个单元提取了三种绿化测量值：)来自陆地卫星遥感图像的归一化差异植被指数（NDVI），)基于土地利用数据的绿地百分比，和)通过深度学习技术从街景图像中提取的眼平面街道绿化。使用病例时间序列设计，在温度项和三种绿化测量值中的每一种之间进行线性交互，进行时间序列分析。还针对不同年龄组、性别类别和特定疾病原因进行了效应修饰估计。
与中度和极端高温都与更高的死亡率风险相关联，与最低死亡率温度（MMT）相比，温度分别在第 90 和 99 百分位数时，相对风险（RR）为 1.022（95%CI：1.000，1.044）和 1.045（95%CI：1.013，1.079）。使用任何一种绿化测量值，绿化程度较高的地区观察到的 RR 较低，但在高温时（与 MMT 相比，第 99 百分位数），使用眼平面街道绿化作为指数时，高低绿化水平之间 RR 的差异更为明显，RR 分别为 1.096（95%CI：1.035，1.161）和 0.985（95%CI：0.920，1.055），NDVI（），1.068（95%CI：1.021，1.117）和 0.990（95%CI：0.906，1.081）用于绿地百分比（），和 1.103（95%CI：1.034，1.177）和 0.943（95%CI：0.841，1.057）用于眼平面街道绿化（）。非意外死亡率和心肺疾病的健康差异仍然存在，且在老年人（年龄≥65 岁）和女性中更为明显。
本研究提供了新的证据，表明与基于 NDVI 和绿地百分比的头顶视角绿化相比，眼平面街道绿化与降低热死亡率风险的关联更强。随着温度的升高，城市绿化的效应修饰趋于放大，在老年人和女性中更为明显。需要采取缓解热应激的策略和健康干预措施，特别是针对可及和可见的绿化，以帮助热敏感人群应对极端高温。https://doi.org/10.1289/EHP12589.
