Background. The current weather warning system aims to reduce mortality from heat and cold stress but still has room to be improved in terms of incorporating other temperature metrics. The aim of this study is to determine how extreme temperature affects mortality in Hong Kong. Methods. An ecological study was used; daily weather data were subdivided into seven temperature metrics. Daily detrended mortality data were stratified by disease groups and analysed using seven different metrics for temperature. The temperature metrics were then compared. Results. A diurnal temperature range (DTR) of ≥8°C leading to an increase in median mortality of up to 16% and a mean temperature change between neighbouring days of ≥4°C leading to an increase in median mortality of up to 6% were the critical thresholds for excess mortality in Hong Kong. Conclusions. This study reveals that mean net effective temperature, DTR, and temperature change between neighbouring days are effective to predict excess mortality in Hong Kong. 1. Background There has been a growing interest in the impact of extreme heat and cold events on health globally. In subtropical Asia, this issue has been investigated in countries including Japan, China, and South Korea. Most heat-related mortality research in Hong Kong has been conducted in the last decade [1–5]. A summary of previous findings in Hong Kong is outlined in Table 1. A U- or J-shaped relationship is observed between temperature and mortality [5]. This is consistent with extant studies [6–8]. This paper will explore seven temperature metrics in relation to mortality in Hong Kong. In particular, the effects on mortality of diurnal temperature range (DTR) and temperature change between neighbouring days are not well understood in the Hong Kong literature. Understanding these effects will enhance the current Hong Kong heat-health weather warning system. Diurnal temperature range (DTR) is the difference between the highest and lowest temperature within a single day [9]. DTR is shown to influence heat-related mortality in Hong Kong [10]. DTR has been decreasing from about 5.5°C in 1947 to about 4°C in 2002 [11]. Traditionally, a large DTR relieves heat stress: it assumes a cool night happens after a hot day. This effect is believed to be important in Melbourne, Australia [12]. Conversely, a large DTR might increase mortality during hot days, particularly with cardiovascular diseases [9] and strokes [13]. A large DTR might also increase blood pressure in the elderly leading to cardiovascular disease [10]. Table 1: Recent studies of
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