京津冀城镇体系与水系结构的时空关系研究

京津冀地区人水关系矛盾突出,分形可以有效描述城镇体系和水系时空演化特征,从而揭示两者演化关系,为城市问题的解决提供一些理论和经验依据。论文采用分形理论中的网格维数和多分维谱,首先分别刻画了两者的时空演化特征,其次探讨了城镇体系和水系结构之间的时空关系,最后探究了水系结构退化的影响因素。主要结论有：① 1990—2010年,京津冀地区建设用地的网格维数升高、自相似性增强、从集聚向分散转变,意味着建设用地朝着空间填充程度增强、有序、分散的方向发展,而水系反之,证明两者具有不同的时空演化方向;② 21世纪10年代,京津冀的人水关系十分紧张,南水北调虽然缓和了京津冀用水问题,改善了大尺度上的水系结构,但在小尺度上改善有限;③ 越靠近城市中心,建设用地分形形态发育越成熟,结构越有序,越靠近外围越混乱无序;④ 京津冀地区水系退化,由自然和人为两方面因素造成,21世纪以后人为因素的影响较为显著。针对京津冀地区水系退化,提出如下政策建议：在城市建设过程中,一方面科学规划城市水系,重视低等级水系的保护;另一方面节约集约利用水资源,完善水资源管理机制。未来,需要进一步探索城市发展和水系的非线性关系,为城市可持续发展提供依据。

Spatiotemporal relationships between urban system and water system in the Beijing-Tianjin-Hebei region

With the rapid development of cities in China, urban environmental problems become increasingly more severe. Clarifying the relationships between urban development and the environment can help solve urban environmental problems. In this study, we took the Beijing-Tianjin-Hebei region as the research area and used fractal method to describe urban system and water system in the region, then to explore the interactions between urban and water systems. The main results and conclusions are: 1) From 1990 to 2010, the fractal dimension of construction land in the Beijing-Tianjin-Hebei region increased, while the fractal dimension of the water system decreased; the bi-fractal characteristic of construction land in the Beijing-Tianjin-Hebei region decreased, while the bi-fractal characteristic of the water system increased; the spatial structure of construction land changed from concentration to dispersion from 1990 to 2015 and the water system became more concentrated. These phenomena illustrate that the spatiotemporal change of construction land and water system had opposite trends in the Beijing-Tianjin-Hebei region. 2) The fractal structure of urban centers is more complete than suburbs. 3) In the second decade of the 21st century, the human-water relationship became tenser. The South-to-North Water Transfer Project eased the severe stress of water in the Beijing-Tianjin-Hebei region, which mainly improved the structure of water system at the large scale. 4) The degradation of water system in the Beijing-Tianjin-Hebei region from 1990 to 2010 was caused by both natural and human factors. In the 21st century, the influence of human factors is more significant. According to the results and conclusions, some policy recommendations are proposed: On the one hand, more consideration should be given to the role of water in the process of urban planning, especially the protection of small-scale water sources and saving water by improving the mechanism of water resources management. On the other hand, more attention should be paid to the improvement of suburban spatial structure by avoiding unlimited urban expansion.