In the changing history of the Yellow River, the third major diversion has led to a sudden northward migration, which radically changed the urban natural and human environment in the flood area and is an ideal research area of the human-earth coupling system. We used a combination of horizontal cross-sectional methods, mathematical statistics and GIS tools to explore the number, spatio-temporal variability characteristics and urban adaptations of the cities flooded by the Yellow River. The results show that: (1) The overflowing of the Yellow River during the seven river-flowing periods gave rise to 29 affected cities. (2) The affected cities were widely distributed in general, but relatively concentrated in the top of the alluvial fan formed by the bursting of the Yellow River, the low-lying Jizhong Plain and the confluence of the Yellow River and Yuhe River. (3) The cities flooded by the Yellow River mainly showed four types of urban adaptability: direct destruction, dismantling, relocation and reinforcement, in which the type of the relocation of floods is dominant, accounting for 45%. (4) The imperial court decision and city scale were important human factors affecting the spatial differentiation and urban adaptability in the sudden disaster environment of the Yellow River. The affected cities in the flooded areas are important models of local conservation significance and sustainable development evolution, which is recommended that they should be included in the national strategy of "Ecological Protection and High-quality Development of the Yellow River Basin" and as an important area for telling the story of the Yellow River.
The Hehuang Valley in the upper reaches of the Yellow River is one of the areas with a long history of human activities, and it is the westernmost part of cultivated land reclamation along the Yellow River. The reconstruction of settlements and cultivated land has practical significance for the study of human activities and global change in this basin. In this paper, a database of settlements and cultivated land in the Hehuang Valley in the late Northern Song Dynasty (1117) was established by combing a large number of historical documents. Based on the spatial distribution of settlements, the grid model was used to reconstruct the cultivated land pattern of the study area with an accuracy of 1 km×1 km. The results show that: (1) The settlements in the Hehuang Valley in the upper reaches of the Yellow River in the late Northern Song Dynasty are concentrated in alluvial and proluvial plains along the main stream of the Yellow River and Huangshui River with relatively low altitude and gentle slope, and the "City" is mainly distributed in the mountain pass in the relatively low altitude area, highlighting its defense function; "States and Castles" are mostly distributed along rivers with relatively flat terrain and relatively geo-safe; however, "Villages" are scattered along the tributaries of rivers, showing the characteristics of disorderly development. (2) The total cultivated land area in the Hehuang Valley is estimated to be about 304.67 km2, with only 16.16% of the grids distributed with cultivated land and only 24.16% of the grids with the highest reclamation rate, among which 74.06% are distributed in the Huangshui Valley and 25.94% along the main stream of the Yellow River, indicating that cultivated land reclamation in the late Northern Song Dynasty is mainly concentrated in the Huangshui River Basin. (3) From the altitude of settlement distribution, 78.09% of the cultivated land grids are distributed in the area of flat terrain with water below 2600 m above sea level, and 21.91% of the grids are distributed in the shallow mountains between 2600 m and 3200 m, indicating that the cultivated land range was not large at that time, and the altitude greatly restricted the expansion of cultivated land, which was mainly distributed in areas with superior irrigation conditions. (4) Rebuilding the spatial pattern of cultivated land based on settlement accords with the fact that cultivated land is distributed with settlements, which is more reliable.
The Wuding River Basin, located in the Loess Plateau of the middle reaches of the Yellow River, is a typical transitional zone and ecologically fragile area in history. Based on the analysis of the historical development process of urban pattern and the coupling relationship between human and land in this process, this paper puts forward the countermeasures and suggestions for the future urban development and ecological protection of the basin in combination with the current situation of urban development. The main findings are as follows: the development and evolution of the urban hub area in the basin was bow shaped in the Tang Dynasty and before, when the natural conditions were better, and the urban spatial layout was mainly based on natural factors; the hub area after the Tang Dynasty presented a triangle pattern, and the urban spatial layout was mainly based on human factors; the contemporary urban pattern of the basin inherited the context of historical development, but the driving force of urban development was mainly based on resources along the Great Wall. The human activities have an impact on the vegetation coverage in some areas; at the same time, the ecological protection policies, such as returning farmland to forests, wind prevention and desertification control, have exerted positive effects. It is suggested that the development of the river basin should be reasonably determined and concentrated around the main cities and towns in combination with the national strategic positioning and regional ecological environment bearing capacity. In addition, the ecological barrier and key prevention and control areas are constructed with the river as the backbone.
The spatial pattern evolution of the cities in the historical Yellow River Basin will help us understand the characteristics and development context of human settlements, which plays a key role in ecological protection and urban development in the Yellow River Basin today. This article uses the time series data of cities (BC763-AD1911) in the CHGIS database of Harvard University, the elevation data of STRM, the regional data of nine major basins in China, and the historical population data. It studies the spatio-temporal pattern evolution of cities in the Yellow River Basin, as well as the influencing factors. The results show that: (1) The changes in the number of cities can be divided into five stages. (2) The first level continous stable region includes the high-density urban area in northern Henan with present Anyang as the center, high-density urban area in Guanzhong with present Xi'an as the center, and the secondary high-density area with Jinan, Taiyuan and Luoyang as the center. The second level continuous stable region includes five important city belts, namely, Weihe River city belt, Fenhe River city belt, northern foot city belt of central Shandong mountainous region, eastern foot city belt of Taihang Mountains and Grand Canal city belt. (3) The average distance of city gravity migration is 32 km, and the average distance of population gravity migration is 95.78 km. The distribution of cities and population is closely related. (4) Natural factors such as temperature and precipitation, elevation, distance from the rivers, downstream avulsions of the Yellow River, as well as human factors such as wars, capital transfer and canals, had jointly influenced the spatial and temporal distribution of cities in the Yellow River Basin.