Substantial increase in human-perceived heatwaves in eastern China in a warmer future

Abstract

Heatwaves describe prolonged periods of excessive heat. The increasing trend in heatwave frequency, duration, and magnitude in a warmer future has been extensively investigated. However, the vast majority of traditional studies on heatwaves consider only the role of air temperature, which is inadequate as a metric for human heat stress. While reported worsening levels in heat stress with global warming are concerning, the changes in heatwaves may not be directly comparable to the temperature increase. The reliable information on future changes in human-perceived heatwaves is still fairly limited. Given this context, we quantified future changes in human-perceived heatwaves in eastern China, where the population is dense and the summers are often sultry, based on dynamic downscaling climate projections and a human thermal comfort index that combines the effect of temperature and humidity. We demonstrated that under the 3.0 °C of global warming (similar to late-century warming projected based on current mitigation policies), the frequency, duration, and magnitude of human-perceived heatwaves in eastern China would increase approximately 5, 4, and 20 times, respectively, relative to the reference period (1986–2005). Human-perceived heatwaves are projected to increase more rapidly than heatwaves solely based on the temperature definition, implying that the escalating heat risk for humans may have been underestimated by previous studies. Moreover, extra cautions need to be given to low-latitude regions, where the smallest changes in the mean temperature will probably be accompanied by the most pronounced increases in human-perceived heatwaves. Our results suggest the urgent demand of reducing greenhouse gas emissions toward mitigating persistent thermal discomfort in the future. Although here we focused on eastern China, our approach to assessing heatwaves can also be readily generalized to address similar problems worldwide.