The predictability of temperature related mortality in the summers of 2022 and 2023

Europe has been identified as a heatwave hotspot, with numerous temperature records having been broken in recent summers. These temperature extremes exact a heavy toll on society; approximately 60,000 heat-related deaths have been estimated for the summer of 2022 alone. With projections showing extreme temperatures becoming more frequent, intense and longer in duration, there is a pressing need to further develop heat-warning systems to help protect, in particular, the most vulnerable members of society. Here we evaluate the skill of daily temperature related mortality forecasts in the context of current numerical weather prediction model capabilities. We consider the summers of 2022 and 2023 as case studies and find that temperature related mortality can, on average, be forecast skilfully up to lead times of approximately one week for these two summers, although we also note the increased predictability in south-western Europe in late-July 2022 coinciding with record breaking temperatures. We further discuss the implications that the non-linear relationship between temperature and temperature related mortality has on temperature related mortality forecast spread and errors, concluding that further developments in forecasting capabilities for extreme temperature events are of key importance for improving temperature related mortality forecasts. Finally, we highlight the implication of these results in a warming climate. In the absence of meaningful adaptation measures or considerable advances in numerical weather prediction capabilities, temperature related mortality forecasts will be associated with larger errors owing to increased climatological temperatures. We emphasise that continued work on understanding the predictability of temperature extremes and temperature related mortality is vital for the further development of heat-warning systems.