Association of mortality and warmer weather below heatwave thresholds, in Berlin, Germany, between 2013 and 2015: a retrospective study

Abstract

BackgroundWhile an association between increased mortality and heatwaves is well known, less is known about higher temperatures ranges below heatwaves and mortality, in urban settings.AimTo establish if there was an association between mortality rates within the population of Berlin, during defined risk periods of daily warmer temperatures between 2013 and 2015.MethodA retrospective secondary data analysis of death counts, population, and temperature data from Berlin. A defined risk periods model of specified temperature ranges of daily minimum and daily maximum temperatures investigated May to September, from 2013 to 2015. A Poisson regression model established incidence rate ratios (IRRs) for mortality. Effect size was estimated in ‘lives lost’.ResultsMortality rates were noticeably increased during defined risk periods for all people aged ≥65 years during daily temperatures of ≥18 to ≤29°C. In people aged ≥75–84 years, during risk period ≥18°C to ≤29°C, incidence risk ratio (IRR) was 1.22 (95% confidence interval [CI] = 1.07 to 1.40, P = 0.004). For females aged 65–74 years, during ≥18°C to ≤29°C, a higher mortality rate was found, compared to males (females: IRR 1.28, 95% CI = 1.15 to 1.42, P<0.001; males: IRR 0.93, 95% CI = 0.78 to 1.10, P = 0.390). Effect size calculation estimated an additional 252 deaths in Berlin, between 2013 and 2015, with 133 deaths in the ≥85-year group.ConclusionAs mortality of older people increased during defined warmer weather, temperatures below heatwave ranges need acknowledgement as a risk factor for health. Policies and health warning systems should include daily minimum temperatures.