Socio-Demographic Factors Heighten the Mortality Risk Linked to Compound Drought-Heatwave Events Under Climate Change

Background: Compound drought-heatwave (CDHW) events present a significant and alarming risk to human health, leading to more severe consequences, including elevated heat-related mortality compared to isolated extreme events. However, there exists a limited understanding of the association of CDHWs with mortality risk, including the modulating effect of socio-demographic factors. This knowledge gap holds critical implications for developing effective public health interventions.Methods: In this retrospective and observational study, we utilize an integrated modeling framework to project future changes in CDHW characteristics and their repercussions on mortality risk. Leveraging panel data from 27,193 older adults in the Chinese Longitudinal Healthy Longevity Survey spanning 2005-2014, we intricately decompose and estimate CDHW-related deaths through Cox proportional hazards model and socio-demographic projections consistent with Shared Socioeconomic Pathways (SSPs).Findings: Our climate-hydrology cascading models, deployed under three SSPs, reveal a notable increasing trend in CDHWs in China during 2015-2100. These increases are most pronounced in the less developed regions like southwestern and northeastern China and northern Xinjiang. In Cox proportional hazards analyses, we find that exposures to CDHWs are associated with an increased all-cause mortality risk of older adults (HR of CDHW frequency: 1.084, 95%CI: 1.070-1.099; HR of CDHW duration: 1.017, 95%CI: 1.015-1.019; HR of CDHW severity: 1.064, 95%CI: 1.055-1.074). Towards the end of this century, CDHW related deaths exhibit a 1.8-fold variation across the three scenarios, with the contribution of CDHW exposures intensifying over time. Projections indicate a premature mortality toll of 19.74 (95%CI: 17.72 to 21.76) million among Chinese individuals aged 65 and older in 2100, linked to CDHW exposures under the highest emission scenario (SSP5-8.5).Interpretation: The study highlights the significant association of CDHWs with mortality risk among older adults in China. Notably, the projected deaths do not necessarily decrease in scenarios with less warming, as the expanding size of vulnerable populations may significantly amplify CDHW-related fatalities. Changes in socio-demographic factors play a more substantial role than CDHW exposure levels in shaping future mortality risks for older adults. Our findings offer valuable insights for designing sustainability policies to safeguard human health under climate change.Funding: The National Natural Science Foundation of China (Grant NO. 41925006).Declaration of Interest: We declare that none of the authors have competing financial or non-financial interests.Ethical Approval: These counties account for approximately 85% of the national total population. CLHLS was approved by the Biomedical Ethics Committee, Peking University, Beijing, China (IRB00001052-13074). Written informed consent was obtained from all participants.