由于城市下垫面高度的空间变异性和不透水面透水面之间错综复杂的空间关系，下垫面降水产流物理机制是城市水文科学研究的难点。项目以北京市凉水河流域为研究对象，结合方庄和亦庄两个实验小区的精细化监测，从描述微观尺度产汇流过程的数学物理方程出发，构建适用于城市下垫面的产汇流数值模型；通过考虑气象强迫因子的取值范围和下垫面条件的空间变异性，采用数值模型在典型汇水单元进行大量随机试验，在统计分析的基础上构建汇水单元尺度降水产流过程宏观本构关系；将所建宏观本构方程与管网和河道汇流模型相耦合，构建尺度协调、物理性强的城市分布式水文模型。通过项目研究，探索“微观网格—汇水单元—流域”的产流升尺度规律，实现城市下垫面降水产流物理机制的定量描述，对科学认识城市雨洪形成过程具有重要意义；通过典型区凉水河流域降水产流机制探索，对首都的防洪减灾和海绵城市建设也具有重要的参考价值。

Due to the high variability of the urban underlying surface and the complex spatial relationship between the permeable surface and impermeable surface, the physical mechanism of the runoff generation over urban underlying surface is a difficult topic in urban hydrology field. The project takes the Liangshui river basin as research object, which is located in the Beijing City. Based on the detailed monitoring of Fangzhuang and Yizhuang experimental areas, a numerical model couples with the Saint Venant equation for surface runoff and Richards equation for soil water movement is developed and validated. By taking into account the range of meteorological forcing factors and the spatial variability of underlying surface conditions, a large number of numerical experiments are carried out in the typical subcatchments using the proposed numerical model. By statistical analysis of the experiment results, The constitutive relation of runoff generation in subcatchment scale is conducted. By coupling the proposed constitutive equation with the pipe network and river channel confluence model, a phisical-based urban hydrological model with coordinated scale is built. The aim of the project is to quantitative describing the physical mechanism of runoff generation over urban underlying surface, and explore the law in increasing scale between misco-grid, subcatchment and basin. The project is of great significance for scientific understanding of the formation process of urban flooding, and also has important reference value for flood control and disaster reduction and sponge city construction in the capital by exploring the runoff generation mechanism of the Liangshui River.