Year: 2026
Type: article
Study design: Observational Study
Abstract: Background Various indicators were suggested to drive heat susceptibility, but it is unclear which are most important for the German context. This study investigates high-dimensional heterogeneity in the effect of hot days on emergency hospitalizations across German districts. Methods We obtained emergency hospitalization rates per 1,000 in 3-day windows for the summers of 2005-2023 from the German DRG-Statistic. These were linked with temperature and dew point information from the E-OBS and HOSTRADA database. A hot day was defined as at least one day above the 98th percentile of the district-level summer heat index. Regional characteristics of the demographic, health/social, and natural/built environment domain were selected from the INKAR database as potential drivers of heterogeneity. We used a generalized random forest clustered at the district-level, where outcome and propensity scores were modelled with fixed effects estimators to control for seasonality and district-level confounding. We divided the conditional average treatment effects (CATE) of heat into quartiles and identified the most important drivers of heterogeneity based on the variable importance and observed distribution across quartiles. Results The occurrence of at least one heat day decreased the emergency hospitalization rate by -0.27 (95%CI: -0.21, -0.33) per 1,000 per 3-day window, with substantial variation across districts. The top three indicators for predicting effect heterogeneity on the district-level were the percentage of people seeking protection, monthly air pollution levels, and living space per person. The observed indicator profile of the highest CATE quartile furthermore included a larger population below age 6, higher car density, and a lower number of hospital beds. Conclusions There is substantial variation in heat susceptibility across and within districts in Germany, with a complex interplay of indicators from different domains driving heterogeneity. Key messages • There is substantial variation in heat susceptibility across and within districts in Germany, with a complex interplay of indicators from different domains driving heterogeneity. • Causal forests present a useful tool for identifying high-dimensional drivers of environmental health inequalities on a regional level.
Authors: M Gueltzow, T Benmarhnia, C Irrgang, M Ebeling
Institutions: Robert Koch Institute, Max Planck Institute for Demographic Research, Scripps Institution of Oceanography, Inserm, École des Hautes Études en Santé Publique, University of California San Diego, Institut de Recherche en Santé, Environnement et Travail, Université de Rennes, Karolinska Institutet
Language: English
Subfield: Health, Toxicology and Mutagenesis
Field: Environmental Science
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,181
OpenAlex ID: W7223654205