Academic journal article Environmental Health Perspectives

Temperature Variability and Mortality: A Multi-Country Study

Academic journal article Environmental Health Perspectives

Temperature Variability and Mortality: A Multi-Country Study

Article excerpt

Introduction

Time series data on daily air pollution concentrations, weather conditions, and daily measures of health outcomes (e.g., mortality, hospital admissions), have been used to assess how environmental factors may contribute to short-term (days to weeks after the environmental exposure) increases in mortality/ morbidity (Bhaskaran et al. 2013; Samet et al. 2000). To date, numerous time series analyses have shown that both cold and hot temperatures are associated with increased risks for a number of health outcomes (Basu and Samet 2002; Basu 2009; Ye et al. 2012). These findings have important implications for understanding the health effects of climate change (Field 2012). However, because climate change increases both the average values and the variability of temperature (Stocker 2014), the health impacts of unstable weather remain unclear (Zanobetti et al. 2012). People may adapt to the usual temperature but may not adapt to the variable temperature. Thus, additional evidence is needed for assessing the health impacts of temperature variability (TV) locally, regionally, and globally.

At the present time, two indices, intraday TV (e.g., diurnal temperature range) and interday TV (e.g., temperature change between neighboring days), have been used to assess the associations between short-term unstable weather and population health (Guo et al. 2011b; Lin et al. 2013; Qiu et al. 2013; Yang et al. 2013). In addition, some studies have used the standard deviation of summer daily mean temperature to represent summer long-term TV (Shi et al. 2015; Zanobetti et al. 2012); this is also a type of interday variability. All of the abovementioned studies assessed the relationships between health outcomes and intra- and interday variability separately. However, because unstable weather is a continuous process, impacts on health may be better captured by considering the intraday and interday variability together when assessing the associations between TV and population health.

In addition, most previous studies of unstable weather and health risks were from one city, one region, or one country, and used different methods. These differences make it difficult to compare the findings directly. We have recently established a Multi-Country multi-City (MCC) collaborative network to assess the effects of weather on mortality globally (Gasparrini et al. 2015a, 2015b; Guo et al. 2014). In this study, we developed a novel method to calculate TV that includes both intraday and interday TV, and we examined TV-mortality associations using the MCC data.

Methods

Data Collection

The MCC data set has been described in previous publications (Gasparrini et al. 2015a, 2015b; Guo et al. 2014). In brief, we obtained daily counts of all cause/non-accidental deaths and weather conditions in 372 communities from 12 countries/regions: Australia (3 cities during 1988-2008), Brazil (18 cities during 1997-2011), Canada (26 cities during 1986-2009), China (6 cities during 2002-2007), Japan (47 prefectures during 1972-2012), Moldova (4 cities during 2001-2010), South Korea (7 cities during 1992-2010), Spain (51 cities during 1990-2010), Taiwan (3 cities during 1994-2007), Thailand (62 provinces during 1999-2008), the United Kingdom (10 regions during 1993-2006), and the United States (135 cities during 1985-2006). Daily weather data included the daily minimum, mean, and maximum temperatures and the relative humidity. The locations are displayed in Figure 1. The Supplemental Material provides the details for data collection in "Data Collection," and Table S1 shows the list of locations.

Calculation of Temperature Variability

Evidence shows that the associations between both intraday and interday TV and health outcomes last for several days (Lin et al. 2013; Yang et al. 2013), suggesting that the impacts of TV on health should be a continuous process. However, these associations were assessed separately, which makes it difficult to assess the overall effects of TV. …

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