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