In brief
At a glance
Quick Facts
- Journal / venue
- Environmental Research
- Authors
- Li et al.
- Publication date
- 2022
- Study type
- Systematic review and meta-analysis
- Peer-reviewed
- Yes
- DOI / link
- 10.1016/j.envres.2022.113359
Study in one sentence
This systematic review and meta-analysis quantified the impact of the urban heat island effect on heat-related mortality, finding that higher urban heat island intensity significantly increases the risk of death during hot weather.
Publication and date
The study, “Urban heat island effect on heat-related mortality: A systematic review and meta-analysis,” was published in the peer-reviewed journal Environmental Research in 2022. The authors are Li and colleagues.
Research question
The researchers aimed to answer: What is the quantitative relationship between urban heat island (UHI) intensity and heat-related mortality, and how do city characteristics modify this relationship?
Method
The study was a systematic review and meta-analysis. The authors searched multiple databases for epidemiological studies that examined the association between UHI intensity and heat-related mortality. They included studies that reported effect estimates (e.g., relative risk, odds ratio) for the UHI effect on mortality during warm seasons or heatwaves. After screening and quality assessment, they pooled the results using random-effects meta-analysis to derive a summary effect size. They also conducted subgroup analyses to explore how factors like climate zone, city size, green space, and study design influenced the association.
Main findings
The meta-analysis found a significant positive association between urban heat island intensity and heat-related mortality. The pooled relative risk for heat-related mortality per 1°C increase in UHI intensity was 1.05 (95% confidence interval: 1.02–1.08), indicating a 5% increase in risk. The effect was stronger in cities with higher population density and less green space. The review also suggested that the UHI effect contributed to a substantial fraction of heat-related deaths during extreme heat events, though the exact attributable fraction varied across studies.
What the findings do not prove
The study does not prove that urban heat islands cause mortality directly; it shows a statistical association based on observational data. The findings cannot be used to predict individual risk, as they reflect population-level effects. Additionally, the review does not establish a causal link between specific urban design features and mortality, only that areas with higher UHI intensity tend to have higher heat-related death rates.
Limitations
The meta-analysis was limited by the heterogeneity of the included studies, which varied in design, population, climate, and UHI measurement methods. Many original studies did not fully control for potential confounders such as air pollution, socioeconomic status, and access to air conditioning. Publication bias may have influenced the pooled estimate, as studies with null findings might be underrepresented. The review also relied on ecological or time-series studies, which cannot account for individual-level exposure or behavior. Finally, the UHI intensity metric itself can be defined in multiple ways, complicating comparisons.
How it compares with previous research
This study aligns with and strengthens earlier research that has consistently found higher heat-related health risks in urban areas compared to surrounding rural areas. Previous reviews had described the UHI effect on health but did not provide a pooled quantitative estimate. This meta-analysis extends that work by synthesizing effect sizes across many studies, confirming a statistically significant increase in mortality risk with greater UHI intensity. It also corroborates findings that green space and lower population density can mitigate the health impacts of urban heat.
Why it matters
Understanding the link between urban heat islands and mortality is critical for public health planning, especially as climate change increases the frequency and intensity of heatwaves. The findings provide evidence that urban design interventions—such as increasing vegetation, creating green roofs, and using reflective building materials—could reduce heat-related deaths. The study also highlights the need for targeted heat-health warning systems and cooling centers in densely built, low-income neighborhoods that often suffer most from urban heat.
Link to the primary paper
The full paper is available at: https://doi.org/10.1016/j.envres.2022.113359 (Li et al., 2022, Environmental Research).
FAQ
What is the urban heat island effect?
The urban heat island (UHI) effect refers to the phenomenon where urban areas experience higher temperatures than their rural surroundings due to human activities and the built environment. Factors like dark surfaces, lack of vegetation, and waste heat from buildings and vehicles contribute to this warming.
How does the urban heat island affect public health?
UHI can increase the risk of heat-related illnesses and deaths, especially during heatwaves. Higher nighttime temperatures in cities prevent the body from recovering, exacerbating cardiovascular and respiratory stress. Vulnerable groups like the elderly, children, and those with pre-existing conditions are at greatest risk.
What can cities do to reduce the health impacts of urban heat islands?
Cities can implement strategies such as increasing tree cover and green spaces, installing green roofs and cool roofs, using reflective building materials, and creating cooling centers. Urban planning that reduces building density and improves ventilation can also help lower temperatures and protect public health.
References
- Li, Y., et al. (2022). Urban heat island effect on heat-related mortality: A systematic review and meta-analysis. Environmental Research, 212, 113359. doi:10.1016/j.envres.2022.113359
- Heaviside, C., Macintyre, H., & Vardoulakis, S. (2017). The urban heat island: implications for health in a changing climate. Current Environmental Health Reports, 4(3), 296-305.
- Oke, T. R. (1982). The energetic basis of the urban heat island. Quarterly Journal of the Royal Meteorological Society, 108(455), 1-24.
- Santamouris, M. (2020). Recent progress on urban overheating and heat island research. Energy and Buildings, 207, 109482.
- Vicedo-Cabrera, A. M., et al. (2021). The burden of heat-related mortality attributable to recent human-induced climate change. Nature Climate Change, 11(6), 492-500.
