Beyond Green Cover: Links Between Greenspace Morphology, Configuration, and Heat-Related Illness in Arizona

Residential greenness has been associated with reduced heat-related illness, yet the specific role of greenspace morphology at the neighborhood scale remains insufficiently understood. This study quantified the relationship between heat-related illness and multiple dimensions of greenspace morphology using an 8-year (2016-2023) unbalanced panel data set comprising 19,021 block-group-year observations across 2,427 census block groups in Arizona, USA. One meter high-resolution National Agricultural Imagery Program aerial imagery was classified to calculate greenspace percentage, number of greenspaces, average size, shape complexity, connectedness, and distantness, at the block group level. We applied conditional spatial autoregressive models with a negative binomial distribution to estimate associations between each morphology metric and yearly heat-related illness counts, adjusting for sociodemographic and geographic covariates. Additional sensitivity analyses evaluated the robustness of findings to overall greenspace amount, local climatic conditions, and alternative exposure specifications. We found higher greenspace percentage, aggregation, shape complexity, connectedness, and density were consistently associated with lower heat-related illness risk. A one-standard deviation increases in shape complexity corresponded to a 12.4% decrease in expected heat-related illness counts (IRR = 0.876, 95% CI: 0.834-0.921). Similarly, increases in greenspace percentage (14.6% decrease; IRR = 0.855, 95% CI: 0.827-0.885), number of greenspace patches (3.7% decrease; IRR = 0.963, 95% CI: 0.937-0.990), average size (4.5% decrease; IRR = 0.955, 95% CI: 0.923-0.989), and connectedness (5.5% decrease; IRR = 0.945, 95% CI: 0.918-0.972) were all protective. In contrast, larger inter-greenspace distances were associated with increased heat-related illness risk (6.1% increase; IRR = 1.061, 95% CI: 1.033-1.091). These associations were generally robust to additional adjustment for local climatic conditions and overall greenspace area. Our findings highlight the critical importance of multiple dimensions of greenspace morphology in relation to heat-related health risks. These results suggest that heat-reduction planning with greening initiatives should consider not only the amount of greenspace but also its spatial configuration to maximize cooling and result in health benefits.