Estimating heat-related mortality burden changes under type-specific green and blue space scenarios in China.

Background: Green and blue spaces (GBS) are assumed to mitigate heat-induced health risks. However, few studies have explored the impact of type-specific GBS changes on heat-related mortality burden.

Objectives: This study aimed to investigate the effect modifications of different GBS types on heat-related mortality risks, and to estimate the changes in mortality burden in multiple GBS scenarios.

Methods: A case time-series study design was utilized based on the daily data on all-cause mortality and temperatures from 2009 to 2020 in 1,085 sub-districts in China. Mortality count data were obtained from the Zhejiang Center for Disease Control and Prevention. Meteorological data on temperature and relative humidity were acquired from the Zhejiang Meteorological Bureau. GBS exposure was assessed by integrating fine-scale population density, GBS boundary from Baidu and OpenStreetMap, and street-view image data from Baidu. Conditional Poisson regression analyses were conducted with the distributed lag non-linear model, incorporating modifiers of type-specific GBS exposure. Changes in heat-attributable mortality under different GBS scenarios were also assessed.

Results: Heat-related mortality risks were lower for populations with high exposure (95%) than for those with low exposure (5%) (1) to overall green spaces, forests, parks, nature reserves, and street greenery, rather than to grasses, farms, and scrubs; and (2) to overall blue spaces, lakes, and rivers, rather than reservoirs, wetlands, or coasts. An increase of 10%, 20%, and 30% exposure to overall green spaces are expected to avoid heat-related mortality burden by 1.6% (95% empirical confidence interval [eCI]: 1.4, 1.9), 3.2% (2.5, 3.9), and 4.8% (3.5, 6.2), respectively, whereas corresponding estimates for overall blue spaces are 5.4% (4.4, 6.4), 10.8% (8.5, 13.3), and 16.2% (12.3, 20.5), respectively. Conversely, a 30% decrease in overall green and blue space exposure will increase the heat-related mortality burden by 4.8% (4.3, 5.2) and 15.9% (15.2, 16.7), respectively.

Discussion: Our study revealed differences in the capacity of various GBS types to mitigate heat-related mortality risks. While the protective effects of GBS may be moderate, targeted planning strategies should prioritize their implementation for maximum benefits in mitigating heat-related health risks. The continuous shrinkage of the GBS would render other efforts futile, such as heat-health action plans. https://doi.org/10.1289/EHP14014.