青藏高原城镇体系的时空演变

城镇体系的形成和发育对区域城镇化进程及社会经济发展起着至关重要的作用,并对生态环境产生重要影响。青藏高原特殊的地理环境与相对落后的社会经济基础,导致城镇体系不甚健全。目前国内外相关研究薄弱,不利于国家生态安全屏障建设及青藏高原可持续发展。为此,本文以建制镇以上的镇区和城市市区为研究对象,结合统计数据与遥感数据,借助GIS空间分析方法对青藏高原1990-2015年城镇体系的空间结构和规模结构进行时空演变格局分析,并采用重心移动模型揭示了青藏高原城镇人口规模和用地规模重心的迁移规律。结果表明：青藏高原城镇空间分布总体呈现出“东南密集、西北稀疏”、“大分散、小集聚”的格局;城镇分布在时间上具有阶段性增长特征且总体趋于集聚,在空间上不均衡程度呈上升趋势但2005年后明显减缓;虽然建制镇数量大幅增长,但96.88%的城镇规模在5万人以下,大中小城市发育不足;城镇人口规模重心呈现“先向西南,再向东北,又向西南”的移动轨迹;城镇用地规模重心呈现“先向东南,再向西北,再向东北”的迁移趋势。本文研究了青藏高原城镇体系的规模结构及其时空演变特征,为青藏高原新型城镇化及城镇空间格局优化提供基础依据;提出了资料缺乏和统计口径不一致的条件下城镇规模的合理估算方法,对我国城镇化相关研究具有一定的参考价值。

Spatiotemporal Evolution of the Urban System in the Tibetan Plateau

The formation and development of the urban system play a vital role in regional urbanization process and socio-economic development. They also have a significant impact on the eco-environment. Due to the special geographical environment and relatively poor socio-economic foundation, the urban system of the Tibetan Plateau seems less developed. Moreover, the relevant literature in Chinese and English are both scarce, hindering the construction of national ecological security barriers and the sustainable development of the Tibetan Plateau. Therefore, based on statistical data, remote sensing data, and GIS spatial analysis methods, this paper took city proper and urban districts (i.e., the core urban areas of cities and officially established towns in China) as the research object, and analyzed the spatiotemporal evolution patterns of the spatial structure and scale structure of the urban system in the Tibetan Plateau during 1990-2015. Meanwhile, based on the urban gravity center movement model, the spatial patterns of the gravity centers of the urban population and urban construction land in the Tibetan Plateau during 1990-2015 were analyzed. We have four major findings. Firstly, the urban spatial distribution of the Tibetan Plateau shows an overall pattern of "intensive in the southeast, sparse in the northwest" and "globally dispersed, locally agglomerated." Secondly, the number of officially established towns increased with different speeds in three stages. The distribution of the urban system as a whole has been more and more agglomerated and the level of spatial imbalance has been on the rise. However, the upward trend has slowed down markedly since 2005. Thirdly, though the number of officially established towns has increased significantly, the urban populations in 96.88% of them are under 50 000. Large, medium, and small cities are underdeveloped. Fourthly, the gravity centers of the urban population and urban construction land during 1990-2015 were all located in the southeast region of the Tibetan Plateau. The gravity centers of the urban population during 1990-2015 shows a movement direction of "first to the southwest, then to the northeast and southwest." It has moved 116.6 km to the southwest during the entire period. The gravity centers of the urban construction land during 1990-2015 shows the movement direction of "first to the southeast, then to the northwest and northeast." It has moved 43.5 km to the northeast during the entire period. Our findings provide basic data to studies of the new type urbanization and the optimization of urban spatial pattern in the Tibetan Plateau. This paper also provides a method for urban scale estimation under the conditions of data deficiency and statistical caliber inconsistency, which will help advance China's urbanization studies.