Heat-Related Mortality

Abstract

Background: As a consequence of global warming, heat waves are expected to become more frequent, more intense, and longer. The elderly and persons with chronic diseases are especially vulnerable to health problems due to heat. This article is devoted to the question of the extent to which the effects of heat waves in Germany are changing over time, and whether preventive health measures are working.

Methods: We use a statistical model to quantify the effect of high mean temperatures on mortality. Within this model, different exposure-response curves for the three temporal intervals 1992-2000, 2001-2010, and 2011-2017 are estimated. Attention is also paid to the delayed effect on mortality of high mean temperatures in the preceding week.

Results: Our analysis reveals a clear, systematic association of the mean temperature in the current week, as well as the mean temperature in the preceding week, with weekly mortality. This association is more pronounced for higher age groups and decreases over the years under analysis, with the exception of a relatively weak effect of heat in southern Germany in 1992-2000. The strongest effects were related to the heat waves in 1994 and 2003, with approximately 10 200 and 9600 fatalities, respectively. Approximately 7800 fatalities were estimated for the summer of 2006, and 4700 and 5200 for 2010 and 2015, respectively.

Conclusion: In Germany, as elsewhere, climate change has been causing more frequent, more intense, and longer periods of heat in the summer. The harmful effect of heat on health is reduced by adaptive processes, presumably including successful preventive measures. Such measures should be extended in the future, and perhaps complemented by other measures in order to further diminish the effect of heat on mortality .

Figure 1

Course of relative mortality rate (exposure–response curves) in central Germany depending on the mean temperature in the current and foregoing weeks in the age group ≥ 85 years. Data: Deaths between the 15th and 40th calendar weeks of the years 1992 to 2017

Figure 2

Adaptation of the statistical model to the data on weekly mortality, Germany, 1992–2017. Shading shows weeks with a mean temperature of more than 20 °C. Only the weeks in the summer half-year (calendar weeks 15 to 40) were modeled.

Figure 3

Comparison of the estimated number of heat-related deaths (red) and excess mortality (blue) in heatwaves in Germany between 1992 and 2017

eFigure 1a

Course of relative mortality rate (exposure–response curves) in Baden–Württemberg depending on mean temperature in current and foregoing weeks by region in the age group ≥ 85 years. Data: Deaths between the 15^th and 40^th calendar weeks of the years 1968 to 1979 and 1988 to 2017 Analysis of an extended time series of mortality for Baden–Württemberg The Statistical Office of Baden-Württemberg has recorded the exact day of decease for all deaths in Baden–Württemberg since 1968. However, analysis of this time series revealed the presence of artifacts for the period 1980 to 1987, so the data from these years had to be removed. Extension of our model to the northern, central, and southern regions of Germany for this longer time series confirms the special role of the years 2001 to 2010, with the heatwave of 2003 constituting a high point for Baden–Württemberg. The foregoing periods show a similar exposure–response curve but without such high mean weekly temperatures. The exposure–response curve is somewhat lower for the period 2011 to 2018—as in the southern region as a whole.

eFigure 1b

Adaptation of the statistical model to the data on weekly mortality, Baden–Württemberg, 1968–2018. The years 1980 to 1987 were not included in the modeling due to irregularities in the data. Shading shows weeks with a mean temperature of more than 20 °C. Only the weeks in the summer half-year (calendar weeks 15 to 40) were modeled.

eFigure 2a

Course of relative mortality rate (exposure–response curves) in northern Germany depending on the mean temperature in the current and foregoing weeks in the age group ≥ 85 years. Data: Deaths between the 15^th and 40^th calendar weeks of the years 1992 to 2017

eFigure 2b

Course of relative mortality rate (exposure–response curves) in central Germany depending on the mean temperature in the current and foregoing weeks in the age group ≥ 85 years. Data: Deaths between the 15^th and 40^th calendar weeks of the years 1992 to 2017

eFigure 2c

Course of relative mortality rate (exposure–response curves) in southern Germany depending on the mean temperature in the current and foregoing weeks in the age group ≥ 85 years. Data: Deaths between the 15th and 40th calendar weeks of the years 1992 to 2017

eFigure 3a

Adaptation of the statistical model to the data on weekly mortality, Germany, 1992–1995. Shading shows weeks with a mean temperature of more than 20 °C. Only the weeks in the summer half-year (calendar weeks 15 to 40) were modeled.

eFigure 3b

Adaptation of the statistical model to the data on weekly mortality, Germany, 2003–2006. Shading shows weeks with a mean temperature of more than 20 °C. Only the weeks in the summer half-year (calendar weeks 15 to 40) were modeled.

eFigure 3c

Adaptation of the statistical model to the data on weekly mortality, Germany, 2008–2011. Shading shows weeks with a mean temperature of more than 20 °C. Only the weeks in the summer half-year (calendar weeks 15 to 40) were modeled.

eFigure 3d

Adaptation of the statistical model to the data on weekly mortality, Germany, 2013–2016. Shading shows weeks with a mean temperature of more than 20 °C. Only the weeks in the summer half-year (calendar weeks 15 to 40) were modeled.

eFigure 4

Estimated number of heat-related deaths in Germany, 1992–2017. The years with a statistically significant estimated number of heat-related deaths are 1992, 1994, 1995, 2001, 2003, 2006, 2010, 2013, and 2015 (in red).

eFigure 5

Mean temperature and modeled mortality in the northern, central, and southern regions for the heatwaves in 1994 and 2003 with adjacent years. For reference the corresponding temperature for the years 1961 to 1990 is given with 95% prediction interval. Shading shows weeks with a mean temperature of more than 20 °C. Weeks with weekly mean temperature beyond the 95% prediction interval are marked as unusually hot. Response to heat in the southern region between 1992 and 2000 To enhance comprehension of the less pronounced response to heat in the southern region between 1992 and 2000, we look again especially at the heatwaves in 1994 and 2003. Comparing the mean temperatures in the three regions of Germany with the reference temperature (the mean for the years 1961 to 1990), it is striking that the temperatures during the 1994 heatwave in the south were still at the upper limit of the prediction interval, while in the central and northern regions they were clearly above the prediction interval. In all three regions the first peak in the temperature curve came in the last week of June. This peak is reflected in the mortality curve, before the maximum temperature in the last week of July. However, while in the south the main peak was only slight (24.2 °C, previously 23.5 °C, difference 0.7 °C), the temperatures in the central and northern regions rose much more (central: 25.1 °C versus 22.3 °C, difference 2.8 °C; north: 24.7 °C versus 19.9 °C, difference 4.8 °C). In 2003, in contrast, the limit of the prediction interval was exceeded in central and southern Germany, while in the north the summer stayed within the normal range.