Heat-Related Mortality in Germany From 1992 to 2021

Abstract

Background: 2018-2020 were unusually warm years in Germany, and the summer of 2018 was the second warmest summer since record-keeping began in 1881. Higher temperatures regularly lead to increased mortality, particularly among the elderly.

Methods: We used weekly data on all-cause mortality and mean temperature from the period 1992-2021 and estimated the number of heat-related deaths in all of Germany, and in the northern, central, and southern regions of Germany, employing a generalized additive model (GAM). To characterize long-term trends, we compared the effect of heat on mortality over the decades.

Results: Our estimate reveals that the unusually high summer temperatures in Germany between 2018 and 2020 led to a statistically significant number of deaths in all three years. There were approximately 8700 heat-related deaths in 2018, 6900 in 2019, and 3700 in 2020. There was no statistically significant heat-related increase in deaths in 2021. A comparison of the past three decades reveals a slight overall decline in the effect of high temperatures on mortality.

Conclusion: Although evidence suggests that there has been some adaptation to heat over the years, the data from 2018-2020 in particular show that heat events remain a significant threat to human health in Germany.

Figure 1

Estimated number of heat-related deaths in Germany in the period 1992–2021. Years with significant numbers of heat-related deaths (5% significance level) are highlighted in red. Years with marginally significant numbers of heat-related deaths (10% significance level) are highlighted in beige. In addition, the estimated numbers of heat-related deaths with 95% confidence intervals are listed in the Table and eTable.

Figure 2

Mortality over time (deaths per 100 000 population) in the period 2018–2021. The gray line shows the reported all-cause mortality, the red line shows the mortality estimated by the model (only in the summer half-year) and the blue line shows the estimated background mortality (expected mortality without heat). Weeks with weekly mean temperatures (averaged across all federal states) above 20 °C are highlighted in yellow. The slightly increased all-cause mortality in spring 2020 and the significantly increased all-cause mortality in winter 2020/21 are explained by the first and second wave of the COVID-19 pandemic. A regional breakdown of the time series can be found in eFigure 1.

Figure 3

Exposure-response curves of the current week (dotted line) and the previous week (solid line) for the 85+ age group in the period 2012–2012, stratified by the three regions “North“, “Central“ and “South“. In each case, the minimum of the exposure-response curve of the previous week is highlighted with a black “x” and marks the temperature threshold above which both the temperature of the previous week and the temperature of the current week result in an increase in mortality. Temperature ranges above the threshold are highlighted in gray. The temperature threshold increases from north to south.

Figure 4

The trend of the exposure-response curves for the three regions “North“, “Central“ and “South“ over the decades. The results for the 85+ age group are depicted because the strongest effects are observed in this age group. The three decades 1992 to 2001 (red), 2002 to 2011 (blue) and 2012 to 2021 (green) show a slightly declining trend which is particularly evident in the central region. Since in the northern region weekly mean temperatures above 25 °C occur significantly less frequently, the estimates in this area are associated with greater uncertainty, a fact that is reflected in the wider confidence intervals.

eFigure 1

The time series of mortality (death per 100 000 population) for the period 2018–2021, stratified by the northern, central and southern regions. The gray line shows the reported all-cause mortality, the red line shows the mortality estimated by the model (only in the summer half-year) and the blue line shows the estimated background mortality. Weeks with weekly mean temperatures (averaged across all federal states) above 20°C are highlighted in yellow. In the years 2018 to 2020, a shorter duration of the heat periods is noted in the northern region. The increased mortality in spring 2020 in the southern region is explained by the first wave of the COVID-19 pandemic. The high mortality rates due to the second wave of the COVID-19 pandemic in the 2020/2021 winter were drawn beyond the limits of the y-axis to avoid distorting the depiction of the summer mortality.

eFigure 2

The heat-related mortality (deaths per 100 000 population) in the period 2018–2021, stratified by region and age group. Despite the shorter duration of the heat periods (efigure 1) in the northern region, the heat-related mortality in the oldest age group in this region is comparable to the central and southern region mortality rates.