随着全球气候变暖和城市化飞速发展，城市洪涝事件频繁发生，我国“城市看海”现象屡见不鲜。揭示城市流域径流变化及其调控机理是城市水循环研究的基础，而由于城市下垫面的高度空间变异性和不透水面与透水面之间错综复杂的空间关系，使得城市下垫面降雨-径流之间的物理机制成为城市水文科学研究的难点。本文以北京市为例，从多尺度探讨了城市流域径流演变的驱动机制，结合室外水文观测实验和数值模拟试验，对城市复杂下垫面降雨-径流关系及其调控机理进行探讨，实现了城市流域降雨-产流物理机制的定量描述，对科学认识城市流域雨洪形成过程具有十分重要的现实意义，对我国海绵城市建设亦具有重要的理论意义和应用价值。

城市流域径流直接驱动要素演变规律的分析，揭示了北京市城市化过程，探讨北京市城市“雨岛效应”及其变化特征；考虑到揭示城市流域径流演变机理的首要任务是识别城市流域径流变化的关键驱动要素，因此，本论文以北京市高度城市化的温榆河流域为例，对该流域不同等级流量变化的关键驱动要素进行识别，从流域尺度揭示城市流域流量演变的驱动机制。通过开展室外水文观测实验，初步认识城市汇水单元降雨-产流的物理机制；耦合一维垂向土壤水分运动方程和二维地表浅水方程，构建基于汇水单元尺度的城市产汇流数值模型，基于大量的数值模拟试验，建立了城市流域径流驱动要素与径流系数的响应函数，并在流域尺度得到验证。论文主要结论如下：

（1）对北京市降水的时空变化规律进行分析，并对城郊降水模式的差异进行探讨，结果表明：北京市中心城区的降水呈现出较明显的变化，1980s年代最大年均降雨量出现在东北部密云一带，而在2000s年代，暴雨中心逐渐向中心城区延伸，在21世纪初期，中心城区成为仅次于东北地区的第二个暴雨中心；21世纪以来北京市年最大3小时和年最大6小时平均降雨量高于前三个十年，而相比于山区区域，中心城区和平原区的这种趋势更加明显。

（2）对城市化流域不同季节全概率流量变化的关键驱动要素进行识别，量化不同驱动要素对不同季节不同级别流量变化的影响，结果表明：城市化效应对不同量级的流量有不同的影响；研究发现城市化效应对春季和冬季中小流量的影响最为显著；降水对夏季洪水的驱动作用最显著，并且降水对夏季洪水的驱动作用随着洪水分位数的增大而增大。

（3）耦合一维垂向土壤水分运动方程和二维地表浅水方程，基于城市下垫面的空间变异性，构建了适用于城市复杂下垫面的地表产汇流计算模型；结合室外水文观测实验和数值模型模拟试验，在统计分析的基础上定量描述城市下垫面产流主要驱动要素与径流系数的响应函数，并在流域尺度上进行初步验证，拟合结果表明：城市汇水单元不透水面积占比与径流系数呈线性函数关系，汇水单元坡度与径流系数呈对数函数关系，汇水单元透水面入渗率与径流系数呈指数函数关系。

Urban flooding events occurred frequently with global climate warming and urbanization, and “observing at the sea in cities” becomes a frequent phenomenon in China. Revealing the mechanism of runoff generation is the basis of the study on urban hydrological recycle. However, the physical mechanism of the relationship between precipitation and runoff in urban areas are always hot topics in urban hydrological studies due to the high spatial variability of urban underlying surface and the complex spatial relationship between impervious and permeable areas. Beijing City is selected as the study area, the mechanism of runoff generation in urban river basins from different scales was investigated in this study. The relationship between precipitation and runoff for the complex underlying surface in urban areas was explored, then these relationships were quantitatively described according to the field experiments and numerical simulations. It is great significant for understanding urban precipitation and runoff processes, and there will be important scientific and practical values for the construction of sponge cities in China.

The temporal and spatial variations of direct drivers for runoff in urban areas were analyzed to investigate the urbanized process, and the characteristics of “precipitation island effect” in Beijing City. Identification of critical drivers is the first task to reveal the mechanism of runoff generation in urban river basins. The Wenyu River basin, which has being experienced a highly urbanized process, is selected as the study area. The critical drivers for different quantiles of discharge were identified in this study to reveal the driving mechanism of runoff generation in urban river basins from the basin scale. The physical mechanism of the relationship between precipitation and runoff were studied through the field hydrological experiment. An urban numerical model for runoff generation and concentration based on the catchment scale was developed by coupling the one-dimensional vertical soil water movement equation and the two-dimensional shallow water equation in this study. The response functions between the driving factors and runoff coefficients were developed on the basis of a large number of numerical model tests, then these functions were validated in the basin scales. The main conclusions are summaried as follows:

(1) The spatiotemporal variability of precipitation in Beijing City are analyzed, and the differences on precipitation patterns between the central area and suburban area were compared each other in this study. The results showed that precipitation in central areas showed obvious changes in Beijing city. The maximum annual precipitation in the 1980s appeared in Miyun County, which is located in the northeast of Beijing City. However, in the 2000s, the storm center gradually extended to the central urban area, and at the beginning of 2010, the central area became the second storm center only after that in Miyun County. Average values of the annual maximum 3-h and 6-h precipitation in the 2010s were higher than those in the past three decades, especially in the urban and suburban areas compared to the mountainous areas.

(2) Critical driving factors for the whole quantiles of discharge in different seasons in a highly urbanized river basin were identified, and the impacts of different drivers for different discharge quantiles in different seasons were quantified. The results showed that the impact of urbanization was different for different discharge quantiles. It was found that the strongest impact of urbanization occurred in spring and winter for low and median quantiles. The role of precipitation is the strongest in the summer, and it increases as it moves towards the upper tail of the discharge distribution.

(3) The numerical model for runoff generation and concentration based on the spatial variations of urban underlying surface was developed by coupling the one-dimensional vertical soil water movement equation and two-dimensional surface shallow water equation, which is suitable for the complex underlying surface in urban areas. The response functions between the runoff coefficients and the driving factors were developed based on the statistical analysis, combined with field hydrological experiments and numerical model tests, and were validated in the basin scales. The results showed that the runoff coefficient showed a linear relationship with the percentage of impervious areas, a logarithmic relationship with the slope of the catchment, and an exponential relationship with the hydraulic conductivity of the permeable surface of the catchment in urban river basins.