Study Exposes Hidden Costs of Urban Heat Islands in 85 European Cities

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A recent study led by the École Polytechnique Fédérale de Lausanne (EPFL) has provided the first comprehensive cost estimate of the impact of urban heat islands on human health. The study, spanning three years and involving 85 European cities, not only considered the well-documented effects of heat islands in the summer but also investigated the protection they offer during winter—a less-explored aspect until now.

Published in the journal Nature Communications, the findings highlight the economic consequences of urban heat islands, revealing their comparable impact on human mortality risk to factors like air pollution, with an average cost of €192 (approximately $210) per adult resident per year. 

Urban heat islands, characterized by elevated temperatures in cities compared to their surrounding rural areas, have long been associated with discomfort during hot weather. However, the EPFL study delves into the multifaceted impacts on human health, drawing attention to increased cardiovascular and respiratory risks, ultimately leading to a reduction in overall life expectancy.

Gabriele Manoli, the corresponding author of the study and a tenure-track assistant professor at EPFL, emphasizes that the study goes beyond the perception of people feeling too hot in the summer and sheds light on the broader health implications. 

The study’s interdisciplinary approach involves integrating data and methods from various fields such as urban climatology, epidemiology, economics, statistics, and mathematical modeling. By combining insights from these diverse disciplines, the researchers aimed to provide tangible economic figures to quantify the impact of urban heat islands on health. The goal was to offer city planners and policymakers a comprehensive understanding of the risks associated with heat islands, allowing for informed decision-making in urban planning and climate mitigation strategies. 

The research is groundbreaking in its examination of urban heat islands across different cities and seasons. It considers both the detrimental effects of heat islands in the summer and the protective aspects they exhibit during winter. The study estimates temperature-related risks for each city and translates them into health costs, considering the net annual effect. Importantly, it addresses the lack of research on the economic impact of urban heat risk and the role of heat islands in winter, offering valuable insights. 

The findings reveal that the threats posed by urban heat islands vary across different cities and seasons. For instance, while the urban heat island of Geneva can lead to four additional heat-related deaths per 100,000 residents per year, it simultaneously prevents 3.4 cold-related deaths.

The study calculates both the costs associated with heat-related effects and the savings attributed to the protective impact of heat islands during cold snaps. The net annual effect, which considers both summer and winter effects, is a key metric in understanding the overall economic impact. 

Cities like Geneva, for example, experience a net cost of €20.7 per adult resident per year due to heat-island-induced mortality, factoring in costs related to heat risk and savings attributed to cold weather protection. On the other hand, some European cities exhibit a negative net cost, indicating savings due to the protection provided by heat islands over extended cold seasons. Helsinki, for instance, shows a net savings of €113.9. 

However, the study’s authors caution against complacency, emphasizing that negative net costs in certain cities should not overshadow the severe health impacts of extreme heat in the summer, which are expected to worsen in the future. They stress the need for continued research to refine cost estimates and explore the complex relationships among heat islands, social inequality, and transportation patterns. 

The EPFL-led study not only quantifies the economic consequences of urban heat islands on human health but also underscores the nuanced variations across cities and seasons. By providing concrete information, the research aims to guide urban policymakers in addressing heat-related risks while balancing the protective benefits offered by heat islands during colder periods. 

Journal Reference  

Wan Ting Katty Huang et al, Economic valuation of temperature-related mortality attributed to urban heat islands in European cities, Nature Communications (2023). DOI: 10.1038/s41467-023-43135-z.