Abstract
Background
Heatwaves are intensifying due to climate change and significantly increase mortality, particularly among older adults. In 2023, the Hessian Heat Action Plan (HHAP) was launched to reduce heat-related deaths. Timely identification of excess mortality is crucial for guiding adaptive responses, yet reporting delays often hinder real-time detection. We developed and assessed an early warning system to identify excess mortality from the previous week during summer months.
Methods
We analyzed weekly all-cause mortality in Hesse, Germany (population 6.4 million; 22% aged ≥65, 7% ≥80) and applied a Bayesian nowcasting model to adjust for reporting delays of 0-12 weeks. Weekly mortality estimates with 95% credible intervals (CIs) were compared to a baseline (mean deaths during five spring weeks of the same year). “Heat weeks” were defined as those with mean temperatures >20 °C. Excess mortality was flagged using three criteria: (1) lower CI > baseline, (2) lower CI > upper baseline CI, and (3) median estimate >5% above baseline. Performance was evaluated using historical heat events (summers 2003, 2015, 2018, 2019) defined by the EuroMOMO method.
Results
Baseline mortality ranged from ∼1,000 to 1,200 deaths/week. All criteria detected substantial excess mortality (>1,400 deaths/week) during 2003 and 2015. Criterion 3 also identified moderate excess mortality (>1,300 deaths/week) in 2018 and 2019. Criterion 2 detected the 2019 event with a two-week delay. Criterion 1 did not detect moderate excess mortality events.
Conclusions
Nowcasting can support heatwave preparedness by enabling near real-time detection of excess mortality. Criterion 3 showed optimal sensitivity and is recommended for routine surveillance. Rapid feedback to HHAP stakeholders may inform timely mid-season interventions and reduce preventable deaths.
Key messages
• Nowcasting excess mortality enables faster response during heatwaves, potentially saving lives.
• A sensitive 5% threshold improves early detection of moderate but meaningful mortality increases.