Swedish Heat-Related Mortality Forecasts for 2025: A Data Driven Approach

Sammanfattning

Climate change is estimated to have caused over 16,000 deaths in major European cities during the summer of 2025, although even colder regions, such as Stockholm, Sweden are seeing increasing heat related death numbers. The public health agency has described heat waves as the most significant hazards emerging from climate change in the country. Researchers suggest that 97% of the heat-attributed deaths during the summer of 2025 in Stockholm were connected to climate change, whilst only 68% of the total European deaths were. There is an urgent need to develop effective early warning systems to help society adapt to our warming climate. Traditional methods of forecasting heat and its public health impacts are being replaced by data driven forecasts, as their efficiency and performance is reaching or exceeding the traditional models. There is a need to verify the skill of data-driven weather forecasts to inform decision makers about predicted health-impacts. The aim of this project is to evaluate the skill of a data-driven mortality forecast in Stockholm by studying the summer of 2025. This study found that the artificial intelligence forecasting system ensemble (AIFS ENS) tends to overestimate temperature related mortality (TRM) in Stockholm, a bias that contrast the evaluation ofsimilar models for other areas. The forecast skill was dependent on both lead time and temperature, with a clear decrease in TRM prediction skill for the hottest days.