城市下垫面对夏季暴雨及洪水的影响研究

发布时间：2018-08-30 16:33

【摘要】：城市化作为人类活动对水循环影响的重要表现形式，一方面通过改变下垫面属性，对地表产汇流特征产生直接影响，另一方面通过地表能量分配及其他城市环境要素（如气溶胶，人为热源等）改变区域降雨特性，从而对地表的水文过程产生间接影响。论文围绕城市地区夏季暴雨及洪水问题，基于多源观测数据和数值模拟手段，开展城市下垫面对降雨以及洪水过程影响规律的研究，对理解城市地区陆气耦合反馈机制以及建立防洪减灾体系有重要的科学价值与实践意义。论文从我国夏季降雨整体时空格局及其与东亚夏季风的关系出发，分析了北京夏季降雨年际变化特征，发现北京夏季降雨在年际上呈波动减少的趋势，与东亚夏季风变化一致；但城区夏季降雨在2000年之后显著增加，与北京建成区面积急剧增加的变化趋势一致。同时，揭示了2008~2012年北京夏季累积降雨量和强降雨频次在空间上有两个聚集中心，分别位于城区以及城市下风向的怀柔、密云和平谷地区。基于耦合城市冠层模型的中尺度气象模式WRF对北京地区2008~2012年夏季降雨的空间格局进行了分析和模拟，从气候角度揭示了城市下垫面对北京地区夏季降雨的影响机制。开发了基于雷达反射回波强度的暴雨云团识别算法SCI-2D，，并将其用于分析夏季暴雨云团通过城区时的演变规律，研究表明城市下垫面对暴雨云团有分离和激发的作用。基于气块浮升理论发现城区地表的热量传输过程改变了大气边界层厚度、抬升凝结高度以及自由对流高度，为对流活动提供了良好的动力和水汽条件，从而使得城区降雨强度和频次得到显著增强。对于典型湖滨城市而言，城市地表热量传输过程对降雨的影响还与湖陆风环流有关。以美国密尔沃基市-密歇根湖地区为例，通过对该地区夏季典型降雨事件的数值模拟和分析，揭示了城市热岛环流和湖陆风环流的耦合效应及其对湖滨城市夏季降雨的影响机制。基于暴雨云团追踪算法TITAN，识别了暴雨云团通过城区时形态和结构的演变特征，进一步验证了北京地区研究得到的结论。以城市化流域为研究对象，定量分析了城市下垫面以及城市化引起的降雨空间分布的改变对流域洪水响应的影响。通过设置虚拟流域及数值实验，发现忽略降雨的空间分布会低估城市化引起的流域洪水量级的增幅，最高可低估50%。此外，降雨空间分布特征对流域年径流量的年际变异性也有显著影响。论文综合了下垫面改变和陆气耦合反馈机制，完善了城市化流域水文响应规律的分析框架。
[Abstract]:Urbanization, as an important form of human activity affecting the water cycle, on the one hand, has a direct impact on the characteristics of surface production and confluence by changing the properties of the underlying surface. On the other hand, the surface energy distribution and other urban environmental factors (such as aerosol, artificial heat source, etc.) change the regional rainfall characteristics, thus have an indirect impact on the surface hydrological process. On the basis of multi-source observation data and numerical simulation method, this paper studies the effects of urban underlying rainfall and flood process on summer rainstorm and flood in urban areas. It is of great scientific value and practical significance to understand the coupling feedback mechanism between land and atmosphere in urban areas and to establish a flood control and disaster reduction system. Based on the analysis of the interannual variation of summer rainfall in Beijing and its relationship with the East Asian summer monsoon, it is found that the summer rainfall in Beijing tends to fluctuate and decrease, which is consistent with the change of the East Asian summer monsoon. However, the summer rainfall in urban areas increased significantly after 2000, which is consistent with the trend of sharp increase in the area of Beijing's built-up areas. At the same time, it is revealed that there are two gathering centers in Beijing from 2008 to 2012, which are located in Huairou and Miyun Heping Valley, respectively, in the urban area and the wind direction under the city. Based on the mesoscale meteorological model (WRF) coupled with urban canopy model, the spatial pattern of summer rainfall in Beijing from 2008 to 2012 was analyzed and simulated, and the influence mechanism of urban underlay on summer rainfall in Beijing was revealed from the point of view of climate. A rainstorm cloud cluster recognition algorithm based on radar echo intensity (SCI-2D,) is developed and applied to analyze the evolution of storm cloud cluster in summer. The research shows that the urban underlay can separate and excite the storm cloud cluster. Based on the theory of air mass floatation, it is found that the heat transfer process on the surface of the urban area changes the thickness of the atmospheric boundary layer, uplift condensation height and free convection height, which provides good power and water vapor conditions for the convective activity. As a result, the intensity and frequency of rainfall in urban areas are significantly enhanced. For typical lakeshore cities, the effect of urban surface heat transfer on rainfall is also related to lake-land wind circulation. Taking the Milwaukey-Lake Michigan area as an example, the typical summer rainfall events in the area are simulated and analyzed. The coupling effect of urban heat island circulation and lake-land monsoon circulation and its influence mechanism on summer rainfall in lakeside cities are revealed. Based on the rainstorm cloud tracking algorithm (TITAN,), the evolution characteristics of the morphology and structure of the storm cloud cluster passing through the urban area are identified, which further verifies the conclusion of the research in Beijing area. Taking the urbanized watershed as the research object, the influence of the urban underlying surface and the change of the spatial distribution of rainfall caused by urbanization on the flood response of the watershed is analyzed quantitatively. By setting up virtual watershed and numerical experiments, it is found that the increase of flood magnitude caused by urbanization can be underestimated by neglecting the spatial distribution of rainfall, and the maximum value can be underestimated by 50%. In addition, the spatial distribution of rainfall also has a significant impact on the annual variability of runoff. In this paper, the change of underlying surface and the coupling feedback mechanism between land and atmosphere are integrated to perfect the analytical framework of the hydrological response law of the urbanized watershed.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TV122

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