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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.