Spatio-Temporal Patterns of County Population Shrinkage and Influencing Factors in the North-South Transitional Zone of China.

Population is the foundation of socio-economic development. However, continued population shrinkage has made the problem of unbalanced and insufficient regional development more prominent, threatening human well-being. How to solve the contradiction between population shrinkage and regional development has become an urgent scientific problem. Therefore, taking a typical underdeveloped mountainous region, the North-South Transitional Zone of China, as an example, we analyzed the spatial and temporal evolution of regional population shrinkage from 2000 to 2020, classified the types of regional population shrinkage, and revealed the key influencing factors and driving mechanisms for the formation of population shrinkage patterns in poor mountainous counties. The results showed that: (1) From 2000 to 2020, the number of counties in the North-South Transitional Zone of China with population shrinkage grew, and the degree of shrinkage increased. The shrinking counties were mainly municipal counties, and the shrinkage types were mainly continuous shrinkage and expansion followed by shrinkage. (2) Spatially, the shrinking counties had significant and strengthening spatial autocorrelation, with obvious characteristics of the contiguous shrinkage of county units, and the shrinkage center of gravity and shrinkage agglomeration areas showed an evolutionary trend of shifting from east to west. The shrinking counties had obvious divergence in both the "east-west" and "north-south" directions. (3) Natural factors had an endogenous rooting role, while human factors had a strong driving role, and the impact of different influencing factors varied significantly. (4) The formation and evolution of the spatial pattern of county population shrinkage was subject to the synergistic effect of natural factors and human factors. The interaction between natural and human factors had a non-linear enhancement effect and a two-factor enhancement effect. The results of this study are expected to provide a scientific basis for coordinating regional human-land relations in order to optimize population-flow governance and sustainable regional development in the North-South Transitional Zone and less-developed regions of China.

Sustainable Population Size at the County Level under Limited Development Policy Constraints: Case Study of the Xihaigu Mountain Area, Northwest China.

Understanding the extent to which demographic changes may affect the prospects of sustainable development is a priority for both academics and policy makers. Accordingly, we attempted to explore the population growth limit of the Xihaigu Mountain area in China. To analyze the optimum population at the county level, the relationship curve between population size and environmental quality was fitted using panel data (2009-2018). The sustainable population size of each county was determined by integrating the population carrying capacity of land resources and optimum population. The results show that the relationship between regional population size and environmental quality conforms to an inverted N-shaped curve. To maintain sustainable development, the population size of Tongxin, Xiji, and Haiyuan should be in the range of 320,800-379,800, 315,800-416,900, and 333,500-416,900, respectively. The current population size of other counties should be maintained, and their surplus construction lands are acceptable to be used for environmentally friendly industries rather than population expansion. We demonstrated a practical approach to calculate a dynamic range of population size under the dual constraints of resource and environment, which overcomes the shortcoming of only considering the maximum carrying capacity to a limited extent. We also identified the population boundary in a "steady-state economy" and quantified planetary boundaries of population in Xihaigu Mountain area using a dynamic sustainable population size. The findings provide decision-making references for the local government.

Multi-Scenario Simulation of Land Use and Habitat Quality in the Guanzhong Plain Urban Agglomeration, China.

Regional habitat quality is a proxy of biodiversity. Simulating changes in land use and habitat quality in urban agglomerations is the scientific basis for promoting the optimal allocation of land resources and building ecological civilizations in urban agglomerations. Therefore, we established a research framework mainly consisting of the Future Land Use Simulation (FLUS) model with the Integrated Valuation of Environmental Services and Tradeoffs (InVEST) model to predict the spatial and temporal distribution of habitat quality. In addition, we set three scenarios which were a natural development scenario, a cultivated land protection scenario, and an ecological protection scenario to analyze the changes of habitat quality in the Guanzhong Plain urban agglomeration in 2035. The results showed that: (1) the FLUS model had an excellent effect on the simulation of land-use change in the Guanzhong Plain urban agglomeration, with an overall accuracy of 0.952 and a kappa coefficient of 0.924. (2) From 2000 to 2035, the cultivated land area of the study area, which was mainly transferred into construction land and grassland, shrank due to the process of urbanization. (3) The habitat quality score of this region gradually decreased from 2000 to 2020, and it continued to decrease to 0.6921 in 2035 under the natural development scenario, while it increased under the other two scenarios. The low-value areas of habitat quality were mainly located in the middle of this region with Xi'an as the core, whereas the high-value areas were mainly distributed in the southern Qinling Mountains and the northern Loess Plateau. (4) Of the different scenarios, the ecological protection scenario had the highest habitat quality, while the natural development scenario had the lowest. Besides this, we also found that the cultivated protection scenario had high habitat quality, which was mainly because the rate of occupation of ecological land was controlled. The results are expected to provide a scientific basis for optimizing the spatial allocation of land resources and promoting the sustainable use of land space in other ecologically fragile urban agglomerations.

[Spatial-temporal Variation of Ozone Concentration and Its Driving Factors in China].

Based on the ozone monitoring data from 2015 to 2017, this study presents the spatial-temporal variation of the ozone concentration and its driving factors in major cities in China via Kriging interpolation, spatial autocorrelation analysis, hotspot analysis, and geographical detector. The results show that:① The ozone pollution became increasingly heavier from 2015 to 2017, with the number of cities in which the 90th percentile of daily maximum 8-h ozone concentration exceeded the air quality standard (GB 3095-2012) increased from 74 to 121, and the proportion of non-attainment days increased from 5.2 percent to 8.1 percent. ② Ozone pollution mainly happened from April to September, during which the non-attainment days contributed 87.5 percent to 95.3 percent to the yearly total number of ozone polluted days. From May to July, ozone concentrations increased the most dramatically, with the proportion of non-attainment days increasing from 10.6 percent in 2015 to 20.5 percent in 2017. Moreover, in 2017, 83.0 percent of the moderate ozone pollution and 91.0 percent of the severe ozone pollution happened from May to July. ③ With the ever increasing ozone concentration over the North China Plain, the high ozone polluted areas such as the Beijing-Tianjin-Hebei region and Yangtze River Delta urban agglomeration are connected geographically. They form the most highly polluted area in China, which includes the Bohai Rim region, Zhongyuan urban agglomeration, Yangtze River Delta urban agglomeration, Shanxi Province, Guanzhong area, and the middle part of Inner Mongolia. In addition, cities in Pearl River Delta region, Chengdu-and-Chongqing urban agglomeration, and the southern part of East China are also gathering speed in terms of ozone pollution, among which Chengdu-and-Chongqing urban agglomeration has become a new ozone-polluted center. ④ The spatial agglomeration of ozone concentration has been enhanced year by year with hot spots distributed mainly in the North China Plain and the middle and lower reaches of the Yangtze River. In contrast, there are cold spots in Northeast China, Southwest China, and Southern China. ⑤ The analysis results from geographical detector show that meteorological factors, industrialization, urbanization, and emissions of ozone precursors all have a significant effect on the distribution of the ozone concentration, but there are also discrepancies in the priority of the driving factors in different regions and seasons.