Analysis of diurnal variation of summmer short-duration rainfall events in the North China plain and five main cities based on hourly rainfall data over 1980—2022

Based on hourly precipitation collected at 294 observation stations in the North China plain from 1980 to 2022 during the summer season (June to August), spatial and temporal distribution characteristics of diurnal variation of short-duration rainfall events in this region are explored. By combining diurnal variations of surface air temperature and prevailing surface winds, diurnal variations and differences in short-duration rainfall events in four cities along the mountains (Beijing, Shijiazhuang, Jinan, and Zhengzhou) and the coastal city (Tianjin) during the earlier (1980—1989) and later (2013—2022) stages of urban development are comprehensively analyzed. The diurnal variation of short-duration rainfall events in the North China plain generally exhibits an evening peak with the peak time shifting from southeast to northwest across the plain. In the later stage of urban development, the diurnal amplitude of short-duration rainfall events decreased to varying degrees in the five cities with the peak time of short-duration rainfall events advancing by 1—2 h in the cities along mountains, while no significant peak time was observed in the coastal city Tianjin. The probability of short-duration rainfall events exceeding 50 mm increased in all the four mountainous cities, and Beijing and Shijiazhuang respectively experienced two-fold and five-fold increases in the probability of heavy precipitation events exceeding 40 mm. However, the coastal city Tianjin witnessed a 43% decrease in the probability of heavy precipitation events exceeding 40 mm. The diurnal variation of short-duration rainfall events in the North China plain is related to thermodynamic effects of local terrain and prevailing surface winds. The urban heat island effect leads to a more pronounced thermal difference between cities along the mountains and the coast and their surrounding terrain, enhancing mountain winds in the cities along the mountains and sea breezes in coastal cities. At the same time, urban warming leads to strengthened surface wind convergence in the afternoon. The wind field changes caused by the evolution of thermal differences in the lower layer of the atmosphere may be an important reason for the earlier diurnal peak of short-duration precipitation processes in cities along the mountains and the concentration of short-duration precipitation processes during the daytime in the coastal city.