Increasing urban and rural population exposures to warm-season concurrent hot days and nights on the North China Plain

Based on the daily minimum and maximum temperatures recorded on the North China Plain (NCP), in this research, we define independent hot days (IHDs), independent hot nights (IHNs), and concurrent hot days and nights (CDHNs) and analyse the spatiotemporal distribution characteristics of these variables. Moreover, based on demographic data derived from Statistical Yearbooks, the exposure of urban and rural populations to CDHNs was also studied. The results show that on the NCP, the average number of heatwave event days was 33.41, and CDHNs, IHDs, and IHNs accounted for 21.07, 38.59, and 40.34% of this total, respectively. Only IHDs showed a nonsignificant decreasing trend. The annual average exposure rates to CDHNs, IHDs, and IHNs were 13.17, 22.75, and 25.29 million person-days, respectively, all of which showed significant increasing trends. The proportion of the urban population exposed to CDHNs was only 12% in the 1960s but increased to 58% in the 2010s. Although the exposure of urban and rural populations showed a significant increasing trend on the NCP, the driving factors showed opposite trends. The exposure of urban populations was mainly driven by the population effect, while the exposure of rural populations was mainly caused by climate effects. In this study, we demonstrated a method for assessing the impacts of heatwave events on exposed populations, thus forming a scientific basis for the development of governmental policies regarding climate change adaptations.