Population exposure to large-scale heatwaves in China for 1961-2015

According to the observed daily maximum temperature data from 756 climate stations in China during 1961–2015, the frequency, intensity, impacted area, and population exposure of the large scale heatwaves (HWs) are calculated by the Intensity-Area-Duration method. During 1961–2015, averagely 24.6 HWs happened every year with an average intensity of 34.4°C, impacting 4.71 million km², around 49.1% of the territory of China. In 2000s, the HW frequency and impacted area have increased by 1.5 times and the intensity has increased by 0.3°C. The largest population exposure is in Central China. There are three stable high value centers of population exposure in China: Northwest China, Central China and North China. The northwest high-value-center is almost stable and isolated. As the north and central high-value-centers are becoming larger, they are likely to merge into one. In 2013, the abnormally strong and stable western Pacific subtropical high and the equally stable Qinghai-Tibet high are the main reasons for the severest HWs in the middle and lower reaches of the Yangtze River. Moreover, North China has started to be invaded by HWs. At the same time, the expansion of the central and north HW centers may involve more populated and developed areas with the threat of HWs. These will affect the social stability, the human health and sustainable development of the national economy.