Subseasonal Prediction of Heat-Related Mortality in Switzerland.

Heatwaves pose a range of severe impacts on human health, including an increase in premature mortality. The summers of 2018 and 2022 are two examples with record-breaking temperatures leading to thousands of heat-related excess deaths in Europe. Some of the extreme temperatures experienced during these summers were predictable several weeks in advance by subseasonal forecasts. Subseasonal forecasts provide weather predictions from 2 weeks to 2 months ahead, offering advance planning capabilities. Nevertheless, there is only limited assessment of the potential for heat-health warning systems at a regional level on subseasonal timescales. Here we combine methods of climate epidemiology and subseasonal forecasts to retrospectively predict the 2018 and 2022 heat-related mortality for the cantons of Zurich and Geneva in Switzerland. The temperature-mortality association for these cantons is estimated using observed daily temperature and mortality during summers between 1990 and 2017. The temperature-mortality association is subsequently combined with bias-corrected subseasonal forecasts at a spatial resolution of 2-km to predict the daily heat-related mortality counts of 2018 and 2022. The mortality predictions are compared against the daily heat-related mortality estimated based on observed temperature during these two summers. Heat-related mortality peaks occurring for a few days can be accurately predicted up to 2 weeks ahead, while longer periods of heat-related mortality lasting a few weeks can be anticipated 3 to even 4 weeks ahead. Our findings demonstrate that subseasonal forecasts are a valuable-but yet untapped-tool for potentially issuing warnings for the excess health burden observed during central European summers.