Spatiotemporal evolution and layout classification of facility agriculture land in urban agglomerations of China

Facility agriculture is one of the most crucial ways to implement the Greater Food concept in modern agriculture. The spatiotemporal evolution and distribution of facility agriculture land can also be essential to optimize its spatial layout for the successful implementation of national food security strategies. In this study, a three-dimensional classification framework of “Human-Land-Region” was constructed for facility agriculture land in urban agglomerations of China. The spatial layout of facility agriculture land was also balanced to match with the labor intensity and amount of facility agriculture land. In this study, the study area was taken as the 19 national-level urban agglomerations in the 14th Five-Year Plan. The parameters were then calculated, including the land area per capita area, geographic concentration, and the Moran’s I of the 19 urban agglomerations for facility agriculture during the period of 2013-2021. Then the spatiotemporal evolution of facility agriculture land was obtained to evaluate the three-dimensional framework in urban agglomerations on the global scale. The typical cities were determined to combine the three-dimensional evaluation, geographic zoning, and the development level of urban agglomerations. Finally, four urban agglomerations were identified as the typical cases, such as the Central Plains, Chengdu-Chongqing, the Yangtze River Delta, and the Mid-southern Liaoning. The modified gravity model and core-edge analysis were also applied to explore the gravitational relationship of facility agriculture among cities within these four urban agglomerations. The facility agriculture land was realized at a downscaled scale from the whole situation to the inner part of typical urban agglomerations. The results indicate that the facility agriculture land in urban agglomerations decreased by 445,900 hectares between 2013 and 2021. There was the regional divergence, in which the Northeast and Central regions shared smaller scales of facility agriculture land, while the South generally had more extensive areas than the North. From 2018 onwards, the distribution of facility agriculture land was shifted from a highly centralized to a slightly decentralized pattern. The urban agglomerations with "high-high clustering" and "low-high clustering" were predominantly found in the eastern regions in various periods, indicating significant spatial dependence. While other areas showed more dispersed distributions. According to the "Human-Land-Region" analysis framework, the layout of facility agricultural land in urban agglomerations was divided into four types: "Growing population with reduced and decentralized lands", "Growing population with increased and centralized lands", "Shrinking population with reduced and centralized lands" and "Shrinking population with reduced and decentralized lands". Urban agglomerations with the first type were found in the relatively slow development in facility agriculture, with a weakening industry pull. While those with the second type were achieved large-scale operations in the concentration of resources. Two main types were accounted for a total of 73.68%, which was the leading type of facility agricultural land in urban agglomeration. There was the severe reduction in the scale of facility agriculture land over the past decade, with a spatial divergence from population changes. Recent trends showed a shift from the centralized supply towards risk diversification. Perennial vegetable plots can be expected to establish in the medium and large cities. The balance between local production and external supply can be strategically designed for facility agriculture within urban agglomerations, in order to enhance the resilience of the supply chain.