Rising temperatures, shifting population: Changes in children’s ambient heat exposure in China

The frequency and intensity of heat waves are increasing, but how these trends translate to changes in the ambient heat to which children are potentially exposed (hereafter, exposures) is not well established. One complicating factor is that it is not only extreme temperatures that change over time, but also the geospatial distribution of children. Another limitation in our understanding is that existing studies often summarize exposure as person-time accumulated above a temperature cutoff, a quantity that confounds the choice of cutoff, the duration of individual exposure, and the share of the population affected. Our study addresses these gaps by developing a double-dual-distributional framework that jointly considers two types of geospatial and temporal distributions (ambient temperatures and child populations) and two types of heat exposure thresholds, namely intensity (heat levels) and duration (hourly exceedance). To illustrate, we assessed potential exposures-the ambient heat conditions experienced-among 250 million children in China, comparing the 1989-1991 and 2019-2021 periods. We found that children's average annual exposure to moderate or stronger heat increased by 385 h, and the share exposed to strong heat for at least 12% of hours rose from 8.1% (24.9 million) to 23.7% (59.1 million). Both rising temperatures and shifts in child population distributions contribute materially to increased heat exposures in China, a finding that suggests the need for forecasts of children's potential heat exposures to consider shifting child population distributions.