Beyond green cover: Greenspace morphology and configuration predict 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 eight-year (2016-2023) unbalanced panel dataset 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. 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). Our findings highlight the critical importance of multiple dimensions of greenspace morphology in mitigating 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.

Extreme heat is a growing health risk, especially in hot regions such as Arizona. While greener neighborhoods are known to reduce heat-related illnesses, less is known about whether the arrangement of green spaces also matters. In this study, we examined how different features of neighborhood green space-such as how much green space there is, how large it is, how connected it is, and how far apart green areas are-relate to heat-related illness over time. Using eight years of data from more than 2,400 neighborhoods across Arizona, we found that neighborhoods with more green space, greener areas that are closer together, better connected, and more evenly distributed experienced fewer heat-related illnesses. In contrast, neighborhoods where green spaces were sparse and far apart had higher risks of heat-related illness. These findings show that reducing heat-related health risks is not just about adding more green space, but also about designing greener neighborhoods in smarter ways. Urban heat-reduction strategies can be more effective when they consider both the amount of greenery and how green spaces are arranged within communities.