Unprecedented Hot Extremes Observed in City Clusters in China during Summer 2022

We report here extreme daytime and nighttime temperatures,severe heatwaves,and compound hot events recorded in China's five most densely populated city clusters in summer 2022.New records were set,with daytime maximum temperatures>42℃in cities along the Yangtze River valley and extreme nighttime temperatures>30℃.Widespread prolonged heatwaves lasting for>40 days and compound hot days occurring for>32 consecutive days were experienced in these city clusters.To explore the possible causes of these extreme events,we analyzed the linkages between the changes in the mean temperatures and hot extremes for different-sized cities in the city clusters.We found that megacities(e.g.,Beijing,Shanghai,Guangzhou,etc.)and large cities(e.g.,Baoding,Wuxi,Foshan,etc.),especially those located in central and eastern China,experienced unprecedented extreme high temperatures,not only in the daytime but also at night.We observed large increases in the mean temperatures and more frequent and more intense hot extremes in cities affected by both the background global warming and intensified urbanization.Megacities and large cities experienced higher and more frequent extreme temperatures and greater warming trends than medium-and small-sized cities(e.g.,Zhangjiakou,Zhenjiang,Yaan,etc.).The evidence of the dependence of temperature trends on a city's size shows that intensified heat island effects may increase the threat of hot extremes in cities undergoing rapid urbanization.