The role of high humidity on extreme-temperature-related mortality in central China

The evidence of non-optimum ambient temperature and humidity-related mortality is widely reported. However, the joint effects of high humidity and extreme temperatures on mortality remain to understand. We collected mortality data and meteorological variables for 91 counties in central China, from 2017 to 2020. A traditional time-series model with a distributed lag non-linear model was first employed to estimate the location-specific associations between extreme temperatures or high humidity and extreme temperatures and mortality. Then, we conducted a meta-analysis to pool the county-specific estimated effect values. A total of 1,196,916 non-accidental deaths occurred during the study period. Extreme heat increased non-accidental mortality with a relative risk (RR) of 1.071 ((95% confidence interval (CI):1.022, 1.121), while extreme cold worsened the risk of stroke mortality by 2.817 (95 CI%: 1.084, 7.321). For the effect of extreme cold, high humidity increased the RR of 3.908 (95 CI%: 2.721, 5.612) in non-accidental mortality and the effect was strongest in stroke with 5.320 (95 CI%: 3.395 vs 8.338). Under the joint effect of extreme cold and high humidity, there is a lagged association with the mortality risks peaked at 12d for non-accidental mortality. High humidity significantly enhances the risk of extreme cold-related non-accidental mortality, especially regarding stroke. Our findings will assist in the development of preparedness and prevention strategies in Hunan Province and even throughout China to reduce the immediate weather-related impacts.