城市化背景下中小流域环境变化对暴雨洪水过程的影响研究

Research on the water cycle under changing environment is one of the key scientific problems in the field of water sciences. Recently, rapid urbanization and regional climate change have triggered intensified and frequent flood disasters in urban basins. Therefore, the research on urban hydrology and the hydrological response for urban basins under changing environment becomes an important scientific problem to guarantee the water and ecosystem security in the urban areas. The Wenyuhe basin in the northern China was chosen as a study area in this project because it is located in Beijing with a high urbanized level, which is one of the largest metropolitan area in China. We firstly analyze the spatial characteristics of the land use/cover change (LUCC) in the Wenyuhe basin and identify their key factors that affect the LUCC in the different periods, and then quantitatively simulate the land use types for the urbanized basin in the future scenarios with the different urbanized levels. Subsequently, we discuss the effects of LUCC and climate change on the storm and flood processes in the urbanized basins. Then the relationship between the flood characteristics and the LUCC and the change in precipitation is established to reveal the response mechanism of storm and flood processes in the urbanized basins under changing environment. Finally, the new methods for rainfall-runoff processes in the urbanized basins are proposed, and the Wenyuhe Hydrological Simulation System is constructed based on the HEC-HMS platform to assess the hydrological effects of urbanization and the future hydrological regimes. The results of this project have important significance to help us understand the hydrological response in urbanized catchments, and will provide scientific and technological basis for the flood protection and disaster mitigation and watershed comprehensive planning for urban basins.

变化环境下的水循环研究是当前水科学研究的核心科学问题。近年来快速城市化发展以及区域气候变化导致城市化流域暴雨洪涝灾害形势严峻，变化环境下城市化流域水文模拟研究已成为保障我国城市水资源安全和生态安全迫切需要解决的一个重要科学问题。本项目以华北地区城市化最显著的温榆河流域为研究区域，在系统分析流域土地利用变化特征的基础上，识别流域土地利用变化的关键因子，定量预测未来不同城市化发展条件下流域土地利用情景；探讨环境变化对流域暴雨洪水过程的影响规律，建立土地利用变化和降水变化与流域洪水特性的关系，揭示变化环境下城市化流域暴雨洪水过程的响应机制；提出适合城市化流域水文过程变化特征的产汇流计算方法，并基于HEC-HMS平台构建温榆河流域水文模拟系统，科学评估城市化的水文效应及未来水文情势变化。项目成果对于科学认识城市化对流域产汇流机制的影响具有重要意义，将为城市化流域防洪减灾及综合规划提供科技支撑。

变化环境下的水循环研究是当前水科学研究的核心科学问题。作为人类活动与气候变化影响最显著的城市化地区，其水科学问题尤其突出且复杂。因此，变化环境下城市水问题研究成为当前学科的研究重点。本研究以北京市及温榆河流域作为研究区域，围绕城市水文效应这一主题，针对城市化发展对区域下垫面、暴雨洪水特征、降雨径流关系及其过程的影响，为城市区域防洪减灾与水资源保护等提供技术支持。综合利用多种数据识诊断北京城市扩展过程中土地利用变化及温榆河流域土地利用特征，显示过去30年城市化建设用地增加明显，导致流域下垫面不透水面积增加显著，揭示了城市化发展与流域下垫面变化的显著相关性。利用多时间尺度降水观测数据调查城市化对降水格局的影响，结果显示城市化对降水表现为明显增强作用，一定程度上抑制了区域降水的下降幅度，但未能改变区域气候变化引起的降水变化趋势，同时对空间格局的影响导致城市化成为降水的次中心。利用城市典型观测站点洪水资料，分析城市化流域洪峰流量与洪量变化规律，除个别站点洪峰流量呈增加趋势外，其他均表现为下降趋势。通过对比城市化前后流域降雨径流关系，表明城市化显著增加城市化流域径流系数，使得洪峰流量增加，峰现时间提前。利用流域地形地貌特征提出适合复杂下垫面条件下的流域产流（综合SCS曲线）与汇流（分布式单位线）计算方法，结合HEC-HMS模型系统平台构建温榆河流域水文模型系统，基于典型暴雨洪水事件验证模型适应性及合理性，模型结果表明了方法的可靠性。通过降水情景分析与下垫面情景模拟，定量评估下垫面变化与降水变化对洪水过程的影响程度，揭示了环境变化对暴雨洪水过程的影响机制。该研究对深入认识北方地区城市化水文效应，了解城市化对降雨径流关系的影响，理解环境变化对城市暴雨洪水的响应机制具有重要意义，为未来城市发展与防灾减灾、城镇扩展与土地可持续利用以及防洪规划提供理论依据。