基于陆-气反馈的湘江中下游城镇化对流域水文过程的影响研究

Impact of urbanization on the storm and flood of watershed has been always a heated topic in hydrology and geography. A better understanding in physical mechanism that urbanization influences the regional rainfall and rainfall-runoff characteristics is crucial to learn effects of urbanization on hydrological processes of watershed. Urbanization can alter the precipitation, runoff yield and concentration in urban areas, while the altered precipitation has direct impact on the runoff yield and hydrological processes in the watershed, which is not well understood. This project aims to study the hydrological process in the urbanized area, in middle and lower reaches of XiangJiang, by combining multi-period remote sensing images(Landsat ETM+/OLI, Google) and topographic maps with long-term observational precipitation and streamflow data. Key attention is paid to reveal the impacts of expanding urbanized area on the regional climate and its feedback on streamflow. First, features of underlying surface and river network systems are acquired and delineated, and changing characteristic of underlying surface and stream structure are studied. Second, rainfall-runoff model featured by feedback between land surface and atmosphere is set up by establishing mesoscale climate model, forcing high spatial resolution land surface model and coupling distributed routing module. The goal of this project is to analyze the evolution pattern of underlying surface and stream networks in the background of urbanization, and impact of increasing impervious area and degraded river systems on urban extreme precipitation and flood. These results can improve our understanding of hydrological cycle in urbanized watershed, and provide scientific support in mitigating floods and hazards in middle and lower reaches of XiangJiang basin.

城镇化对流域暴雨和洪水的影响一直是水文学和地理学的研究热点，探究城镇化对局地降雨和产流汇影响的物理机制，对于准确认识城镇化流域水循环过程具有重要意义。城镇化改变了城市局地降雨和下垫面产汇流特性，而城镇化引起的降雨变化会直接影响产汇流特性和流域水文过程，这点目前还未得到充分认识。本项目以我国中部快速城镇化典型地区-湘江中下游为研究区，从热量和水分平衡角度，借助多期Landsat ETM+/OLI、Google遥感影像、地形图和长序列的降雨径流资料，构建陆-气反馈的中尺度气候模式，驱动高分辨率陆面模式，耦合分布式河道汇流模块，综合数理统计与数值模拟，分析城镇化过程中下垫面和水系变化特征，研究下垫面改变对城市暴雨的影响规律，探究下垫面和河流改变对流域暴雨洪水的影响过程。本项目深入认识城镇化对流域水循环过程的影响机制，研究成果可为该地区防洪减灾和社会可持续发展提供科学支撑。

城市化对流域暴雨和洪水的影响一直是水文学和地理学的研究热点，探究城市化对局地降雨和产汇流的影响，对于准确认识城市化流域水循环过程具有重要意义。本项目以长江中、下游城市群为研究区，借助多期遥感影像、地形图和长序列的降雨径流数据，分析研究区城市化过程中下垫面和河流变化特征，研究城市化与极端洪涝事件的关系，构建基于陆-气反馈的降雨-径流模拟系统，探讨城市化对流域水循环过程的影响机制。研究结果表明：（1）城市用地面积持续增长，年扩张率维持在5%左右，城市形态重心在近30年发生阶段性迁移，城市扩张是引起河流消失的最主要的原因。（2）城市地区夏季温度升温显著，水循环过程加速，夏季降雨呈显著增加趋势，夏季大雨、暴雨、极端降雨增加明显，流域洪涝风险加剧。（3）基于WRF和VIC，我们构建了研究区的中尺度天气模式和分布式水文模型，模型可以很好地模拟研究区的气候特征和水文过程。（4）城市扩张使城市夏季日平均气温、日最低气温和日最高气温增加0.75、1.06和0.45℃，随着城市化进程城市热岛效应在加强；城市化导致低层大气中湿度减少，造成城市干岛效应；同时，城市化导致降雨增多，引起城市雨岛效应，而随着城市化进程，城市雨岛效应在减弱。本项目研究成果可为该区域防洪减灾和城市可持续发展提供科学支撑。