Humidity may amplify the temperature-related health risks in the context of climate change.

Humidity and temperature may pose joint effects on human health. However, current temperature-related risk assessments generally focus on univariate temperature statistics, leading to inaccurate risk estimation. By combining temperature and humidity intensities as compound temperature-humidity events (hereinafter as compound events), we examined the effects of humidity in temperature-related health risks in the context of climate change in China using ambulance dispatch data, and further determined the high-risk types and thresholds of compound events. After assessing the health risks, compound events are defined as: i) warm and wet event: temperature ≥ 90th, humidity ≥ 55th and 70%; ii) warm and dry event: temperature ≥ 80th, humidity ≤ 10th; iii) cold and wet event: temperature ≤ 15th, humidity ≥ 70th and 70%; iv) cold and dry event: temperature ≤ 5th and humidity ≤ 25th. Results reveal that humidity can amplify the temperature-related health risks. Higher risks were found during cold and dry events and warm and wet events, posing risks as 1.102 (1.045–1.161) and 1.093 (1.068–1.118) respectively. Compound events mainly occurred in Southeast China during 1979–2019, while the frequency and gripped regions are projected to increase by 2100, and climate change will amplify these trends. Since humidity would exacerbate temperature-related health risks, therefore multiple meteorological parameters are needed in defining adverse weather conditions and conducting risk assessment accurately.