Changing humid heat exposure in Germany – where senior citizens will be most affected and why

Europe is currently the fastest warming continent and even in temperate countries such as Germany the number of extreme temperature days has been rising. These pose increasing risks to human health and wellbeing. Yet, while dry heat and urban heat islands have received substantial scientific attention, humid heat episodes have historically been rare in Central Europe. Recent observations, however, indicate that their frequency and intensity are growing, and projections suggest that regions once considered climatically temperate may increasingly encounter conditions previously confined to the tropics. In this study, we examine humid heat stress in terms of days with exceptionally high vapor pressure exceeding a critical threshold of 18.8 hPa.  With a particular focus on elderly populations (65+), we quantify humid heat stress in Germany for a historical reference period (1961-1990) calculated from ERA5 re-analysis, and for the future under a global warming level of +2 °C using an ensemble of convection permitting RCM simulations at 3 km resolution.  An integration with official population counts and projections yields humid heat exposure estimates. Beyond spatio-temporal trends, the analysis decomposes the drivers of change into three components: (i) climate change, (ii) population growth or decline, and (iii) demographic ageing.

Data analysis for the reference period revealed pronounced spatial disparities: average annual humid heat days peak in Berlin and Brandenburg, whereas humid heat is most seldom in Thuringia and Schleswig-Holstein. While population densities are the highest in the three German city states and lowest in the eastern part of Germany, this pattern is also reflected in the proportion of senior citizens. By combining humid heat frequency, population, and elderly share, we derive the number of “senior citizen humid heat events.” In the reference period, this indicator is dominated by population distribution resulting in maximum exposure in Berlin, Hamburg and Bremen. Preliminary results for +2 °C global warming suggest significant changes in climatic hotspots. Ongoing work will assess how these and other spatial patterns are expected to propagate in detail, before quantifying the relative contributions of climate, population, and demographic change to future humid heat exposure in Germany.