Escalated heatwave mortality risk in sub-Saharan Africa under recent warming trend.

Evidence from high-income countries indicates populations are adapting to frequent heatwaves, but similar trends in resource-constrained regions remain unknown. We analyzed mortality data from 11 Health and Demographic Surveillance Systems across sub-Saharan Africa (2005 to 2015) to examine temporal changes in heat-related mortality risk. Contrary to global trends, our findings suggest that heat vulnerability is increasing across African populations. Nighttime heatwave mortality risk increased significantly between 2005 to 2010 and 2011 to 2015 [OR from 1.02 (95% CI: 0.87 to 1.13) to 1.18 (95% CI: 1.13 to 1.23)], while daytime heatwaves showed no significant impact. Compound heatwaves transformed from nonsignificant to significant risk factors [OR = 1.11 (95% CI: 1.03 to 1.22)]. Males showed increased risks across all heatwave types, females only for nighttime and compound heat. Children under 5 showed universal risk increases, while the elderly showed the highest increases for nighttime and compound heat. These findings suggest that physiological adaptation alone is insufficient to cope with increasingly frequent heatwaves without adequate socioeconomic resources. Heightened nighttime vulnerability underscores the need for context-specific adaptations reflecting Africa's distinct conditions.