Impacts of the 2015 Heat Waves on Mortality in the Czech Republic—A Comparison with Previous Heat Waves

Abstract

Abstract:This study aimed to assess the impacts of heat waves during the summer of 2015 on mortality in the Czech Republic and to compare them with those of heat waves back to the previous record-breaking summer of 1994. We analyzed daily natural-cause mortality across the country's entire population. A mortality baseline was determined using generalized additive models adjusted for long-term trends, seasonal and weekly cycles, and identified heat waves. Mortality deviations from the baseline were calculated to quantify excess mortality during heat waves, defined as periods of at least three consecutive days with mean daily temperature higher than the 95th percentile of annual distribution. The summer of 2015 was record-breaking in the total duration of heat waves as well as their total heat load. Consequently, the impact of the major heat wave in 2015 on the increase in excess mortality relative to the baseline was greater than during the previous record-breaking heat wave in 1994 (265% vs. 240%). Excess mortality was comparable among the younger age group (0-64 years) and the elderly (65+ years) in the 1994 major heat wave while it was significantly larger among the elderly in 2015. The results suggest that the total heat load of a heat wave needs to be considered when assessing its impact on mortality, as the cumulative excess heat factor explains the magnitude of excess mortality during a heat wave better than other characteristics such as duration or average daily mean temperature during the heat wave. Comparison of the mortality impacts of the 2015 and 1994 major heat waves suggests that the recently reported decline in overall heat-related mortality in Central Europe has abated and simple extrapolation of the trend would lead to biased conclusions even for the near future. Further research is needed toward understanding the additional mitigation measures required to prevent heat-related mortality in the Czech Republic and elsewhere.

Heat-related mortality during hot summers in Polish cities

“…Similarly to the results of Oudin Åström et al (2016), the additional mortality caused by heat in the area on the coast is lower than inland. This is also in accordance with previous studies, such as Urban et al (2017) and Medina-Ramon and Schwartz (2007). The largest number of deaths associated to the occurrence of high air temperature was recorded in cities with the highest population density (and, simultaneously, with the largest population).…”

“…Hajat and Kosatsky (2010) and Hondula et al (2015) explain such a difference in mortality rates by the age of population and economic conditions. Urban et al (2017) draws attention to the differences in the physical environment, while Son et al (2016) to the differences in urban vegetation.…”

Temporal trends in human vulnerability to excessive heat

“…Of the studies that have examined heat wave-to-heat wave variability in human impacts, only in the Nitschke et al (2011) study are heat impacts greater with the later event, though this is framed in the context that the later (2009) event was unprecedented for Adelaide, Australia. For the summer of 2015 in the Czech Republic, heat related mortality was similar to that of 1994, despite a baseline decline in heat vulnerability (Urban et al 2017). For the remaining studies, all show general declines; for instance, Palecki et al (2001) and Weisskopf et al (2002) show mortality in the midwestern USA in a 1999 heat wave was far lower than that of the 1995 'Chicago Heat Wave'; Smoyer (1998) shows in St. Louis, USA the 1995 heat event was less impactful than a 1980 event; and Tan et al (2007) show similar decreases between heat events in 1998 and 2003 in Shanghai, China.…”

“…Todd and Valleron (2015) In central France, the ratio of mortality attributed to high temperatures declined significantly from 1968-2009. Urban et al (2017) The summer of 2015 was as pronounced as the summer of 1994 in terms of heat related mortality. Wang et al (2016) In the US, heat stroke hospitalizations have decreased substantially between 1999 and 2010.…”

Ocean and atmosphere influence on the 2015 European heatwave

“…The heatwave began in late June in Western Europe and then spread towards Southern and Eastern Central Europe, with several cities reporting record high temperatures (Sippel et al 2016). The exceptionally warm conditions led to extreme drought over most of central Europe (Orth et al 2016) with several heat-related deaths (Muthers et al 2017, Urban et al 2017, Výberči et al 2018. With future climate projections estimating mean summer temperatures over Europe to increase by 0.6°-1.5°C in 2016-2035 (Kirtman et al 2013), heatwaves will become more common (Meehl and Tebaldi 2004, Schär et al 2004, Ballester et al 2010, Lhotka et al 2018.…”