Background China published its inaugural national heat-health action plan (HHAP) in 2023, but the mortality burden associated with temperatures exceeding the heat alert thresholds specified by this HHAP (maximum temperatures >35, 37, or 40 °C) remains unknown. We aimed to estimate the historical and future mortality burden associated with temperatures above the heat alert thresholds of the Chinese national HHAP.

Methods We conducted time-series analyses to estimate the mortality burden associated with temperatures exceeding the three heat alert thresholds from 2016-2019 in Jiangsu Province (including 13 cities, population ∼80.7 million), China. A quasi-Poisson regression in conjunction with a distributed lag non-linear model was used to estimate the dose-response association between maximum temperature and mortality risk from 2016-2019, adjusting for potential covariates. We then projected the future mortality burden associated with temperatures exceeding these thresholds under three distinct levels of greenhouse gas (GHG) emission scenarios via scenario shared socioeconomic pathways [SSP] 1-2.6 (low), SSP2-4.5 (intermediate), and SSP5-8.5 (high), respectively, by assuming that there will be no adaptation to heat. Climate scenarios derived from the General Circulation Model (GCM) under the Coupled Model Intercomparison Project Phase 6 (CMIP6) were used.

Results From 2016-2019, temperatures above 35 °C were associated with 0.51% of mortality, including 0.40% associated with 35 °C – 37 °C and 0.11% associated with >37 °C. Heat-related mortality risk was most prominent in those who were single/divorced/widowed and had <10 years of education. Under SSP2-4.5, compared with the 2020s, the excess mortality associated with >37 °C would increase by 1.4 times in the 2050s and 1.7 times in the 2090s. Under SSP5-8.5, the annual number of days with maximum temperature >37 °C would approximately double every 20 years (67 days annually in the 2090s). Consequently, compared with the 2020s, the excess mortality associated with >37 °C would increase by 2.8 times in the 2050s and 18.4 times in the 2090s.

Conclusion Significant mortality risk is associated with temperatures above the lowest heat alert threshold of the Chinese national HHAP (35 °C). If the high GHG emission scenario occurred, the annual number of days and excess mortality associated with maximum temperatures >37 °C would largely increase in the coming decades.