Academic journal article Environmental Health Perspectives

Space-Time Covariation of Mortality with Temperature: A Systematic Study of Deaths in France, 1968-2009

Academic journal article Environmental Health Perspectives

Space-Time Covariation of Mortality with Temperature: A Systematic Study of Deaths in France, 1968-2009

Article excerpt

Introduction

The variation of daily mortality with the temperature at the time of death has repeatedly been found to be U/J-shaped, with increased mortality at both low and high temperatures (Rau 2007). Generalized additive models (GAM) (Hastie and Tibshirani 1990; Wood 2006) provide a powerful framework to model the temperature-mortality relationship and estimate its minimum [sometimes referred to as the minimum mortality temperature

(MMT)], while taking into account potential confounding factors (Curriero et al. 2002).

Comparative studies at different latitudes found repeatedly that the temperature at which mortality was minimal was higher in places where the mean summer temperature (MST) was higher. For example, the authors of an observational study in seven different European settings (Keatinge et al. 2000) found that the observed 3[degrees]C-wide band with the lowest mortality ranged from 14.3-17.3[degrees]C in north Finland, to 19.3-22.3[degrees]C in London, and to 22.7-25.7[degrees]C in Athens. In 11 eastern U.S. cities, the MMT correlated with the latitude (Curriero et al. 2002). Similar results were obtained in Spain, where 13 cities were compared (Iniguez et al. 2010). One interpretation of the variation of the MMT with temperature of the place for which it is computed, as of other parameters [e.g., excess winter mortality, found to be highest in countries with milder winters (McKee 1989)], is that human behaviors adapt to local climatic conditions (Keatinge et al. 2000; Rau 2007). Drawing conclusions from this geographic observation about the possible adaptability of human populations to future climate change requires observing that, similarly, MMT at a given location changes over time when climate changes.

Herein, we report our analysis of the temperature-mortality relationship in continental France during the 42 years between 1968 and 2009. Continental France is approximately 900 km x 900 km, and exhibits broad climatic diversity (Laaidi et al. 2006). The study covered a period of warming in France and worldwide (National Aeronautics and Space Administration Goddard Institute for Space Studies 2015). Our primary goal was to describe the temperature-mortality relationship at the highest spatial resolution possible to include small towns and rural settings that have so far been poorly investigated. The second goal was to determine whether MMT increased in parallel to the MST rise observed in France over the last four decades.

Methods

Climate data. We used the ENSEMBLES gridded observational data set (E-OBS) (Haylock et al. 2008; van den Besselaar et al. 2011), which provides the daily mean temperatures, precipitations, and average sea-level pressures in Europe with a 0.25[degrees]-latitude x 0.25[degrees]-longitude resolution.

Discretization of space. The temperature-mortality relationship was studied within each 0.50[degrees]-latitude x 0.50[degrees]-longitude "square" (approximately 30 km x 30 km) of a grid placed over the map of continental France. This grid was built by aggregating four 0.25[degrees]-latitude x 0.25[degrees]-longitude squares of the E-OBS data set, starting at 40.625[degrees] latitude and -5.625[degrees] longitude and ending at 10.625[degrees] latitude and 51.875[degrees] longitude, yielding 295 squares (Figure 1), for which the daily mean temperatures, precipitations, and average sea-level pressures were obtained by averaging the four 0.25[degrees]-latitude x 0.25[degrees]-longitude E-OBS database source values.

The smallest administrative territorial partition of France is the "commune" [the French version of the second level of Local Administrative Units (LAU 2) in the nomenclature of the European Union (Eurostat 2015)]. Sociodemographic data used herein are available at this level. There are roughly 36,000 communes in continental France, with wide variability in terms of surface and population. Each of the communes was attached to the 0. …

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