作为世界上最大的发展中国家，我国自1978年改革开放以来经历了快速的城市化进程。城市化是人类活动改变地表的主要过程，它涉及到生产生活方式的改变以及社会经济的动态变迁。在城市高速发展的过程中，往往会伴随着大量人为热源在城市区域聚集，城市建筑对大气动力和热力的影响会改变对流，导致降水存在着明显的城乡差异。同时，由于城市区域不透水面的增加，城市地表渗水能力减弱，以及城市居民的密集化，强降水事件可以在短时间内造成局部内涝等自然灾害，严重威胁人类生命和财产安全。因此，深入探究城市化与降水的内在联系对于建设可持续和有弹性的城市环境至关重要。

基于高分辨率的土地覆盖数据集和长时间序列的小时降水观测资料，本研究从极端降水和降水事件两个角度出发，通过对比分析城市站和乡村站的降水差异，评估了城市化对1978-2021年中国中东部暖季（5-9月）降水的影响。主要研究结果如下：

（1）城市地区更容易出现极端降水事件，但极端降水的城乡差异表现出明显的区域特征。从长期趋势来看，城市化会抑制东北地区和京津冀地区极端降水的发生，增强华南、四川盆地和长江下游流域极端降水的发生。而在日变化上，城市站的极端降水强度在整个日循环中均高于乡村站，城市地区极端降水的增强主要出现在午后和夜间的降水高峰时段，最大差值为1.79 mm/h，出现在16:00 LST。同时我们还发现，城市地区的极端降水量和强度会随着城市热岛（UHI）效应的增强而增大，且在强UHI天数下，强降水事件一般在傍晚（18:00 LST）开始，到深夜结束。

（2）从降水事件的角度出发分析城市降水效应，结果表明城市地区更容易发生持续时间短、降水量大、强度大的降水事件。短时（2-5小时）降水事件的数目、降水量和强度均表现出城市地区大于乡村地区的现象，其中小时降水强度的城乡差异最明显，高达0.18 mm/h。与低强度降水事件相比，城市地区可能会发生更多降水量大的大雨（HP）和暴雨（TP）事件。其中，TP事件的数目、降水量和强度的城乡差异均呈增长趋势，增长速度分别为1.73 %/decade、1.23 %/decade和0.93 %/decade。同时，降水事件起止时间的城乡差异主要来自于傍晚至夜间（17:00-22:00 LST）开始的强降水事件。在不同持续时间下，逐小时降水强度在降水事件开始时（尤其是前2个小时）城乡差异较大，越接近降水结束，城乡差异越小。

本论文基于小时降水观测的研究结果表明快速城市化已经成为影响中国中东部极端降水分布的重要因素，并且在强UHI日的傍晚以及降水事件开始时，城市化作用加强，这为未来研究城市降水效应的影响因素提供了参考信息。

As the world's largest developing country, China has experienced rapid urbanization since its economic reforms and open-up in 1978. Urbanization is the main process by which human activity alters the land surface, which involves changes in productive lifestyles and dynamic socio-economic shifts. The process of rapid urban development is often accompanied by massive anthropogenic heat sources clustering in urban areas, and the impact of urban buildings on atmospheric dynamics and thermodynamics alters convection, leading to significant urban-rural differences in precipitation. Meanwhile, due to the increase in urban impervious surfaces, the weakening of urban surface water infiltration capacity, and the densification of urban dwellings, heavy precipitation events can cause natural disasters such as localised flooding in a short period of time, posing a serious threat to human life and property. Therefore, it is essential to deeply explore the intrinsic links between urbanization and precipitation for building sustainable and resilient urban environments.

Based on a high-resolution land cover dataset and long time series of hourly observational precipitation data, and from the perspectives of both extreme precipitation and precipitation events, this study assesses the impact of urbanization on the precipitation in the warm season (May-September) during 1978-2021 over central and eastern China by comparatively analyzing the difference in precipitation between urban and rural stations. The main findings are as follows.

(1) Urban areas were more prone to extreme precipitation events, but the urban-rural differences in extreme precipitation showed clear regional characteristics. In terms of long-term trends, urbanization suppressed the occurrence of extreme precipitation in northeast China and Beijing-Tianjin-Hebei region, and enhanced the occurrence of extreme precipitation in southern China, Sichuan Basin, and the Lower Yangtze River valley. As for the diurnal variation, the extreme precipitation intensity at urban stations was higher than that at rural stations throughout the diurnal cycle, and the enhancement of extreme precipitation in urban areas mainly appeared during the precipitation peak hours in the late afternoon and at night, with a maximum difference of 1.79 mm/h, which occurred at 16:00 LST.We also found that the extreme precipitation amount and intensity in urban areas increased with the enhancement of the urban heat island (UHI) effect, and that the strong precipitation events generally started in the evening (18:00 LST) and ended in the late night during the strong UHI days.

(2) Analyzing the urban precipitation effect from the perspective of events, the results showed that urban areas were more likely to experience precipitation events of short duration, high amount and high intensity. The number, amount and intensity of short-duration (2-5 h) precipitation events presented a phenomenon that was greater in urban areas than in rural areas, with the most pronounced urban-rural difference in hourly precipitation intensity being as high as 0.18 mm/h. Compared with low-intensity precipitation events, urban areas were likely to experience more heavy precipitation (HP) and torrential precipitation (TP) events with high precipitation amounts. Among them, the urban-rural differences in the number , amount and intensity of TP events exhibited an increasing trend, with the growth speed of 1.73 %/decade, 1.23 %/decade, and 0.93 %/decade, respectively. At the same time, the urban-rural differences in the beginning and ending time of precipitation events were mainly due to the strong precipitation events that began in the evening to night time (17:00 - 22:00 LST). In different durations, the hourly precipitation intensity varied more between urban and rural areas at the beginning of the precipitation event (especially in the first 2 h), and less between urban and rural areas the closer the end of the precipitation. The closer to the ending time of the precipitation, the smaller the urban-rural differences.

The results of this paper based on hourly precipitation observations indicated that rapid urbanization has become an important factor influencing the distribution of extreme precipitation over central and eastern China. Moreover, the urbanization effect is strengthened in the evening of strong UHI day and at the beginning of precipitation event, which provides information for future research on the factors influencing the urban precipitation effect.