Climate change dominates the increasing exposure of global population to compound heatwave and humidity extremes in the future

Abstract

Abstract Under global warming, compound event arises increasing attract as it can lead to a growing impact on water resources management, human society, and ecosystem, especially for the compound heatwave and humidity extremes (CHHE), which can exert harmful influence on human health. However, the understanding of changes in CHHE both in the historical and future, and attribution of global population exposure to CHHE are far from enough. In this study, we selected the wet-bulb temperature (Tw) to define the CHHE, and used the Coupled Model Intercomparison Project Phase 6 (CMIP6) data to investigate future changes in global CHHE. Furthermore, we quantified the relative contributions of population, climate change and their interaction effect to the change in population exposure to CHHE. We found that all scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5) show an increasing trend of CHHE. For SSP5-8.5, the global mean Tw will increase by 7°C, and the northern North America and central Africa experience warming approaching 10°C by the end of 21st century. Under SSP3-7.0 and SSP5-8.5, large equatorial regions will witness Tw exceeding 35°C resulting in an exposure of 105 million person-days. All the scenarios presented an increase in population exposure to CHHE, which is mainly contributed by climate change (50%-90%) rather than population under different scenarios. We also found that the contribution of population-climate interaction is significantly higher in Africa than in other regions, which mainly due to high population growth rates in the future. Our study provides scientific basis and useful information for the development of adaptation strategies to reduce disaster risks caused by CHHE.