华北平原及沿山和沿海五个城市夏季短历时降水过程的日变化分析

Analysis of diurnal variation of the short-duration rainfall event in the North China Plain and five cities along mountains and along the coast during the summer season

中文关键词:  短历时降水过程,日变化,城市效应,地形,华北平原

英文关键词:Short-duration rainfall event, Diurnal variations, Urban effect, Topography, the North China Plain

中文摘要:

      利用华北平原294个国家自动站1980—2022年夏季（6—8月）逐时降水资料，分析了华北平原夏季短历时降水过程的日变化时空分布特征，结合地面气温、地面风的日变化，综合分析了四个沿山城市北京、石家庄、济南、郑州和沿海城市天津，在城市发展前期（1980—1989年）和后期（2013—2022年）短历时降水过程日变化特征及差异。结果表明：华北平原短历时降水过程整体呈现傍晚单峰的日变化特征；平原站点的达峰时间自东南向西北滞后。五个主要城市在城市发展后期，短历时降水过程的日振幅都出现不同程度的减小；沿山城市短历时降水过程日峰值出现时间提前了1—2个小时，而沿海城市天津无明显峰值时间，且高值时段提前；沿山城市50 mm以上短历时降水过程概率均有所增加，其中北京和石家庄40 mm以上的降水过程概率分别增加了2倍和5倍，而沿海城市天津40 mm以上的降水过程概率减小了43%。华北平原短历时降水过程的日变化与局地地形的热动力作用和地面盛行风有关。城市局地增温效应导致沿山沿海城市与周围地形热力差异更加明显，增强了沿山城市的山风和沿海城市的海风；同时，城市增温导致的城市午后地面风辐合增强。地面风场的变化可能是沿山城市短历时降水过程日峰值提前、沿海城市短历时降水过程集中时段变为白天的重要原因。

英文摘要:

      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), the spatial and temporal distribution characteristics of diurnal variation of short-duration rainfall events in the region is explored. By combining the diurnal variations of near-surface air temperature and prevailing surface winds, it comprehensively analyzed the diurnal variations and differences in short-duration rainfall events in four cities along the mountains (Beijing, Shijiazhuang, Jinan, and Zhengzhou) and coastal city Tianjin during the early (1980-1989) and later (2013-2022) stages of urban development. 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 hours in the cities along mountains and no significant peak time observed in the coastal city of Tianjin. The probability of short-duration rainfall events exceeding 50 mm increased in all four mountainous cities, with Beijing and Shijiazhuang experiencing a two-fold and five-fold increase, respectively, in the probability of heavy precipitation events exceeding 40 mm. However, the coastal city of 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 was related to the thermodynamic effects of local terrain and the prevailing near-surface winds. The urban heat island effect led to a more pronounced thermal difference between cities along the mountains and the coast and their surrounding terrain, enhancing mountain winds for cities along the mountains and sea breezes for coastal cities. At the same time, urban warming led to increased surface wind convergence in the afternoon. The changes in surface wind patterns may have been important reasons 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.