Drivers of associations between daytime-nighttime compound temperature extremes and mortality in China.

ABSTRACT

BACKGROUND: Temperature extremes are anticipated to become more frequent and more intense under the context of climate change. While current evidence on health effects of compound extreme temperature event is scarce. METHODS: This nationwide cross-sectional study collected daily data on weather and mortality for 161 Chinese districts/counties during 2007-2013. A quasi-Poisson generalized linear model was first applied to assess effects of daytime-only, nighttime-only and compound daytime-nighttime heat wave (and cold spell) on cause-specific mortality. Then a random-effect meta-analysis was used to produce pooled estimates at national level. Stratification analyses were performed by relative humidity, individual and regional characteristics. RESULTS: Here we show that mortality risks of compound daytime-nighttime temperature extremes are much higher than those occurring only in the daytime or nighttime. Humid weather further exaggerates the mortality risk during heat waves, while dry air enhances the risk during cold weather. People who are elderly, illiterate, and those with ischemic heart disease and respiratory disease are particularly vulnerable to extreme temperature. At the community-level, population size, urbanization rate, proportion of elderly and PM2.5 are positively associated with increased risks associated with heat waves. Temperature, humidity and normalized difference vegetation index are positively associated with the effects of cold weather, with an opposite trend for latitude and diurnal temperature range. CONCLUSIONS: This nationwide study highlights the importance of incorporating compound daytime-nighttime extreme temperature events and humid conditions into early warning systems and urban design/planning.

Ongoing climate change has exaggerated the frequency and intensity of severe climate events, leading to substantial health and socioeconomic consequences. We assessed deaths in China during periods when many extreme climate events occurred at the same or similar times. We looked at deaths occurring during periods when both daytime and nighttime temperatures were very hot or cold. We found more serious health effects were seen when temperatures remained hot or cold during the day and night compared to when it was just hot or cold during the day or night. Other factors including humidity, preexisting heart or respiratory disease and age also impacted the risk of death. Our study highlights the detrimental health effects of many extreme climate events occurring together and the need for both people and governments to consider approaches to reduce these negative effects.