Greenspace modifies the associations between heat and mortality: A systematic review and meta-analysis of observational studies

Muhammad Mainuddin Patwary , Imran Chowdhury Sakib, Md Ismay Azam Badhon, Mondira Bardhan, Mohammad Javad Zare Sakhvidi, Dana Sikder, Payam Dadvand, Michelle L. Bell, Matthew Browning , Thomas Astell-Burt, Md Pervez Kabir, Peter James

Greenspace has been increasingly examined for its potential associations with heat-related mortality. However, quantitative synthesis of evidence on this association remains limited. We conducted a systematic review and meta-analysis of observational studies published through July 20, 2025, examining the relationship between effect modification of greenspace on heat-related mortality risk. We systematically searched and synthesized data from 45 studies encompassing over 290 million deaths. A random-effects meta-analysis was conducted, comparing high-greenness areas to low-greenness areas during heat events (≥95th percentile temperature). Risk of bias was assessed using the Office of Health Assessment and Translation (OHAT) tool, and the quality of evidence was evaluated using GRADE criteria. Publication bias was assessed through funnel plots, Egger’s test, and the Trim and Fill method. We found that high-greenness areas were associated with a lower risk of all-cause mortality during heat (≥95th percentile), with a pooled relative risk (RR) of 1.09 (95%CI: 1.02–1.17, n=11), compared to low greenness areas (pooled RR: 1.24, 95%CI: 1.11–1.38, n=11) with substantial heterogeneity (I²=97%). Sensitivity analyses showed consistent associations between high greenness and reduced mortality risk. Funnel plot indicated some asymmetry, and Egger’s test suggested publication bias (p < 0.05), possibly reflecting small-study effects. Risk of bias assessment showed that 55% of studies had low risk across domains. GRADE evaluation downgraded the overall quality of evidence to “low” due to substantial heterogeneity and publication bias. This quantitative evidence provides suggestive evidence of an association between higher greenspace exposure and reduced heat-related mortality risk. While urban greening initiatives may contribute to mitigating heat-related mortality, the presence of heterogeneity and potential publication bias highlights the need for further research with standardized methods to better characterize this relationship.