Evidence on How the Landscape Configuration of Green-Blue Spaces Modifies Heat-Related Mortality Risk

While green-blue spaces (GBSs) are known to mitigate heat-related health risks, the influence of their landscape configurations remains underexplored epidemiologically. This study quantifies how GBS exposure and its specific spatial configurations modify the association between heat and mortality. We conducted a case time series study across 1064 subdistricts in Zhejiang Province, China (2009-2020), using high-resolution data and a conditional Poisson regression with a distributed lag nonlinear model. We developed a green-blue space exposure index (GBSEI) and four landscape configuration indices: coupling (GBSCI), shape (GBSSI), fragmentation (GBSFI), and connectivity (GBSCOI). Higher GBS exposure (95th vs 5th percentile of GBSEI) was associated with significantly lower heat-related mortality risk (ratio of relative risk [RRR] = 1.13, 95% CI of 1.08-1.18). Specific landscape configurations were also crucial: higher coupling and connectivity, and less complex shapes, were associated with 7% (95% CI of 1%, 13%), 7% (95% CI of 1%, 13%), and 6% (95% CI of 2%, 10%) lower mortality risks, respectively. While GBS fragmentation showed no significant effect on all-cause mortality, it was linked to a lower risk of heat-related cardiovascular mortality. These protective effects were more pronounced at extreme heat levels and were stronger in females. Notably, while the protective effect of GBS quantity was universal, the benefits of optimized configurations were observed exclusively in high-income subdistricts. This study provides direct epidemiological evidence that not only GBS quantity but also its quality (specifically higher coupling, connectivity, and lower shape complexity) significantly protect against heat-related mortality, offering critical insights for evidence-based urban planning to design climate-resilient cities.