Abstract:Based on the hourly maximum temperature observations from 19 national meteorological stations during the summers of 2008-2021, this paper analyzes the spatial distribution of high temperature (HT) hours and the features of interdecadal, intraseasonal and diurnal variabilities in Beijing. The results show that the numbers of both HT days and HT hours are much greater in the dountown area and the south of the city, but less in the north and west parts as the result of the combined influences of topography and urban heat island effect. Among them, the Haidian, Fengtai and Changping districts are the most concentrated areas of HT days and hours. On the intraseasonal scale, the HT hours in Beijing are mainly concentrated in the period from late mid-June to early mid-July, which is the period before the beginning of the rainy season in North China. The first dekad of July is the most concentrated period of HT activities. On the diurnal variation, the HT activities can be seen mainly from 09:00 BT to 21:00 BT, particularly concentrated from 14:00 BT to 17:00 BT. In addition, linear regression is also employed in this paper to fit the relationship between maximum temperature and HT hours. The correlation coefficient between the fitting result and the observation reaches as high as 0.82. In Beijing, for each 1℃ increase in maximum temperature over the 35℃ threshold, the HT hours increase by about 1.7 hours. The HT hours in Beijing also exhibits an obvious interdecadal variability. The distribution of the differences of accumulated summer HT hours between 2015-2021 and 2008-2014 is quite different from the spatial distribution of HT hours in climatic state. The area with large interdecadal differences is not located at the central part of HT days or HT hours. Relative to the period of 2008-2014, the HT hours in 2015-2021 are commonly added from 11:00 BT to 19:00 BT, which means the HT periods in Beijing tend to start earlier and end later in the latter period.