Abstract: Extreme heat events (EHEs) are a major cause of weather-related deaths. People who live in cities may be more vulnerable to EHE because the urban heat island (UHI) effect causes a slower cooling process at night, and thus provides little relief from the heat stresses of the day. Although UHI is a well-documented phenomenon, relatively little information in the literature is available about its characteristics during EHEs. Moreover, urban warming in addition to greenhouse gas-induced warming has not been taken into account explicitly in climate change simulations to date. Under the background of global climate change and rapid urbanization in China, the magnitude of future warming and the health risk of EHEs may be significantly underestimated in urban areas. With the forecast of global warming continuing into the foreseeable future, extreme heat events will become more intense, more frequent, and longer lasting with climate change. The impacts of urbanization on extreme heat events have attracted an increasing attention in recent years. The potential exposure of urban populations to climate change will be enhanced by local factors with the development of urbanization. This review systematically collates research results in three main areas: observational evidence of trends in EHEs in relation to urbanization, numerical simulation experiments of the impact of urbanization on temperature and heat stress during EHEs, and epidemiological study of excess mortality associated with urbanization during EHEs. Most observational and simulation studies show that urban heat island results in an increase in the extent and intensity of extreme heat in cities. Inhabitants of urban areas may experience increasing heat-related health risk. Heat island also significantly contributes to the long-term increasing trends in urban EHEs. The epidemiological studies reveal that heat island caused by urbanization has great impacts on excess mortality in cities during EHEs. Finally, future avenues of research are speculated, including: synergistic effect of extreme heat with other environmental factors, heat-health warning systems, mapping extreme heat health risk, and future projection of EHEs due to climate change and urban growth.

Key words: urbanization, climate change, extreme heat, excess mortality

摘要： 目前有关城市热岛效应的时空分布特征及其对气温变化趋势的影响已有大量研究,但对于极端高温—热岛效应相互作用、城市化对高温热胁迫及其健康后果的影响等研究还不够深入,在进行未来气候变化预估时也很少考虑城市的影响。在气候变化、中国城市化快速发展和人口老龄化的背景下,这将严重低估城市未来的变暖幅度以及城市极端高温的健康风险。随着近年来气候变暖所导致的高温热浪事件频发,城市化对极端高温事件的影响引起了广泛关注。本文对国内外陆续开展的城市热岛效应影响极端高温及其长期趋势的观测事实、城市极端高温数值模拟、城市高温期间超额死亡率的流行病学研究等方面所取得的成果进行了系统性的总结和评述。大部分观测和数值模拟研究都发现,城市热岛效应加剧了城市极端高温发生的范围和强度,增加了城市居民的高温健康风险,对城市极端高温的长期上升趋势也有重要贡献;流行病学研究表明,城市化引起的热岛效应对极端高温期间的死亡率有着重要影响。最后,对城市化影响极端高温未来的研究方向进行了探讨。

关键词: 城市化, 气候变化, 极端高温, 超额死亡率