Opposite Changes Caused by Human Activities in the Occurrence of High Health-Risk Compound Hot-Dry and Hot-Wet Events in China

Abstract Compared to a single high-temperature anomaly, compound heat anomalies associated with humidity, such as Compound Hot-Dry Events (CHDEs) and Hot-Wet Events (CHWEs), pose a greater threat to human health. However, it is still unclear how human activities and natural forcings affect the likelihood of these health-related compound heat events. Here we utilize ambulance dispatch data along with meteorological data to study the human activities impact on high health-risk CHDEs and CHWEs in China. We show that relying solely on temperature standards without considering humidity may underestimate the health risks of compound heat events on populations. We find that during the past 40 years, anthropogenic activities in China have increased and decreased the occurrence of high health-risk CHDEs and CHWEs to 2.34 and 0.63 times from 1979 to 2014, respectively, particularly in the middle and lower reaches of the Yangtze River region, compared to natural forcing. And in the future, the opposing contribution of anthropogenic activities will be likely to persist under different shared socioeconomic pathways. We also speculate that, in the future up to 2060, under the carbon-neutral scenario, the frequencies of high health-risk CHDEs and CHWEs caused by human activities can be reduced by one-half and over one-fifth, respectively, compared to the high-emissions scenario (SSP-5.85). Our results provide initial guidance to recognize and asses the health risk of compound events under anthropogenic global warming.