Paper Reviewed
Zhang, Y., Yu, C., Yang, J., Zhang, L. and Cui, F. 2017. Diurnal temperature range in relation to daily mortality and years of life lost in Wuhan, China. International Journal of Environmental Research and Public Health 14: 891, doi:10.3390/ijerph14080891.

A number of studies have examined the relationship between temperature and human mortality. However, few of them have utilized the diurnal temperature range (DTR) as the dependent, or causative, variable. The latest study to incorporate DTR into such an analysis comes from Zhang et al. (2017).

DTR, as defined in their work, is the difference between daily maximum and minimum temperature, which difference provides a measure of diurnal temperature variability and is an analog of weather stability. Using daily meteorological data and records of all registered deaths in Wuhan, central China, between 2009 and 2012, Zhang et al. performed a series of statistical procedures to eventually estimate the exposure-response impact of the DTR on both human mortality (including non-accidental deaths and those due to cardiorespiratory, cardiovascular, respiratory, stroke and ischemic heart disease causes) and years of life lost (YLL). In addition, they performed subgroup analyses to stratify their findings by age, gender and education level.

Results indicated that a 1°C increase in DTR at lag 0-1 days significantly increased daily non-accidental mortality by 0.65% and cardiovascular-specific mortality by 1.12%. The relationships between DTR and deaths due to other investigated causes (cardiorespiratory, respiratory, stroke and ischemic heart disease) were not significant. Nor was there any significant relationship between DTR and YLL for any of the cause-specific mortalities investigated.

In stratifying their findings by subgroups for the two mortality categories that did have a significant relationship with DTR (non-accidental and cardiovascular deaths), Zhang et al. found that, "compared with males and younger persons, females and the elderly suffered more significantly and substantially from both increased mortality and YLL in relation to a high DTR." Furthermore, and somewhat surprisingly, they also found that those who had obtained a higher degree of education were more susceptible to increased mortality and YLL from a DTR increase than those who were less educated.

Of significance to Zhang et al.'s findings is the fact that multiple researchers have reported a decline in DTR in recent decades at locations all across the globe in conjunction with a rise in global temperatures. For China, in particular, Shen et al. (2014) recently calculated a country-wide DTR decrease at a mean rate of 0.157°C/decade based on an analysis of 479 weather stations over the period 1962 to 2011; and they cited the works of a number of other authors who also determined that the "DTR decreased significantly in China over the past several decades, including Karl et al. (1991, 1993), Kukla and Karl (1993), Dai et al. (1997, 1999), Liu et al. (2004), Ye et al. (2010), Zhou and Ren (2011), Wang and Dickinson (2013), Xia (2013) and Wang et al. (2014). Consequently, it would appear that if global temperatures continue to rise and the DTR continues to decline, there will likely be less cases of non-accidental and cardiovascular deaths in the future.

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