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. 2014 Oct 28:13:89.
doi: 10.1186/1476-069X-13-89.

Acclimatization across space and time in the effects of temperature on mortality: a time-series analysis

Mihye Lee  1 , Francesco Nordio, Antonella Zanobetti, Patrick Kinney, Robert Vautard, Joel Schwartz
Affiliations

Acclimatization across space and time in the effects of temperature on mortality: a time-series analysis

Mihye Lee et al. Environ Health. .

Abstract

Background: Climate change has increased the days of unseasonal temperature. Although many studies have examined the association between temperature and mortality, few have examined the timing of exposure where whether this association varies depending on the exposure month even at the same temperature. Therefore, we investigated monthly differences in the effects of temperature on mortality in a study comprising a wide range of weather and years, and we also investigated heterogeneity among regions.

Methods: We analyzed 38,005,616 deaths from 148 cities in the U.S. from 1973 through 2006. We fit city specific Poisson regressions to examine the effect of temperature on mortality separately for each month of the year, using penalized splines. We used cluster analysis to group cities with similar weather patterns, and combined results across cities within clusters using meta-smoothing.

Results: There was substantial variation in the effects of the same temperature by month. Heat effects were larger in the spring and early summer and cold effects were larger in late fall. In addition, heat effects were larger in clusters where high temperatures were less common, and vice versa for cold effects.

Conclusions: The effects of a given temperature on mortality vary spatially and temporally based on how unusual it is for that time and location. This suggests changes in variability of temperature may be more important for health as climate changes than changes of mean temperature. More emphasis should be placed on warnings targeted to early heat/cold temperature for the season or month rather than focusing only on the extremes.

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Figures

Figure 1
Figure 1
Distribution of study area by cluster: Each color represents the cluster ID and the number of cities which belongs to each cluster is in the parentheses.
Figure 2
Figure 2
Heat effects by month in cluster 1: The percent change in mortality in association with heat compared to the mortality at the mean temperature in corresponding month differs by month.
Figure 3
Figure 3
Monthly trend of mortality at 25°C by cluster: The mortality response at 25°C compared to the mortality at the mean temperature in corresponding month and cluster shows the U-shape trajectories.
Figure 4
Figure 4
Cold effects by month in cluster 2: The percent change in mortality in association with cold compared to the mortality at the mean temperature in corresponding month differs by month.
Figure 5
Figure 5
Heat effects in July by cluster: The response to the heat effects differs by regions and it depends on the relative scale rather than the absolute temperature.
Figure 6
Figure 6
Cold effects in January by cluster: The response to the cold effects differs by regions and it depends on the relative scale rather than the absolute temperature.
Figure 7
Figure 7
Sensitivity analysis on visibility - monthly trends of mortality at 25°C.
See this image and copyright information in PMC

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