Objectives. To quantify heat-related deaths in Ho Chi Minh City, Vietnam, caused by the urban heat island (UHI) and explore factors that may alleviate the impact of UHIs.Methods. We estimated district-specific meteorological conditions from 2010 to 2013using the dynamic downscaling model and calculated the attributable fraction and number of mortalities resulting from the total, extreme, and mild heat in each district. The difference in attributable fraction of total heat between the central and outer districts was classified as the attributable fraction resulting from the UHI. The association among attributable fraction, attributable number with a green space, population density, and budget revenue of each district was then explored.Results. The temperature-mortality relationship between the central and outer areas was almost identical. The attributable fraction resulting from the UHI was 0.42%, which was contributed by the difference in temperature distribution between the 2 areas. Every 1-squarekilometer increase in green space per 1000 people can prevent 7.4 deaths caused by heat. urban and surrounding rural areas. The UHI effect can also be observed within a city (i.e., when the inner city is warmer than the outer city). People living in urban areas, especially the inner areas of cities, are subsequently exposed to excessive heat. From a health perspective, this is concerning because it can increase heat-related mortality and morbidity risks. More than half of the global population lives in urban areas, and this proportion is expected to rise to 85% by 2100. 5 Therefore, the impact of UHIs on human health could be substantial and will likely be amplified in the future. In this study, we focused on the UHI effect within a city. Previous studies have investigated heat-related mortality variations within particular cities; however, they either lack spatial temperature data at finer scales (such as at the district level within a city) 6-8 or neglect district-specific mortality. 9 This has hindered their ability to compare the mortality-temperature association between the central and outer districts of the same city. In addition, to our knowledge no study has directly quantified the magnitude of the UHI effect on mortality (i.e., the number of deaths attributable to the UHI effect). City authorities are now considering some UHI mitigation activities, such as land-use planning and tree planting. 10 These activities, however, need to be supported by empirical studies that can answer questions such as "To what extent does the UHI effect cause mortality?" and "To what extent can the planting of trees/green space prevent deaths caused by the UHI effect?" Here, we examine these questions by quantifying the deaths attributable to the UHI effect in Ho Chi Minh (HCM) City, Vietnam, and exploring factors that may alleviate UHI impacts. HCM City is a tropical megacity undergoing rapid urbanization, and it is the most populous city in Vietnam; thus, it offers an interesting setting for this study.

1 2 km WBGT 33 m WBGT This study revealed the impacts of land use and anthropogenic heat on the heterogeneous spatial patterns of temperature and the thermal index in Shibuya ward in Tokyo, which contains a commercial area, residential area, and park within 1-2 km 2 . Observations revealed that temperature in the residential area was slightly higher than that in the commercial area during the daytime. The park had the lowest temperature of the three. At night, temperature in the commercial area was the highest and that in the park was the lowest. Additionally, observations showed that a surface inversion layer developed over the park at night, whereas a surface unstable layer occurred during the nighttime from the ground level to a height of at least 33 m over the commercial area. Measurement with a thermal camera showed that there were almost no differences in the surface skin temperature between the commercial and residential areas during the day and night. It is considered that these results are caused by the large thermal inertial associated with the large urban surface area, large building volume, and large heat capacity. These results were supported by numerical experiments with a multilayer urban canopy model. Unlike the temperature, there was almost no difference in the wet-bulb globe temperature between the commercial area and the park, resulting from higher humidity in the park.

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