[Evolution of Urban Expansion Pattern and Its Impact on the Quality of the Ecological Environment in the Beijing-Tianjin-Hebei Urban Agglomeration].

Clarifying the impacts of urban land expansion on changes in the quality of the ecological environment in the Beijing-Tianjin-Hebei （BTH） urban agglomeration is of great significance for the high-quality development of the BTH urban agglomeration and the construction of ecological civilization. The urban expansion rate， urban expansion intensity， and landscape pattern index were introduced to analyze the urban expansion pattern of the BTH urban agglomeration from 2000 to 2020， the integrated remote sensing eco-environment index （IRSEI） was constructed based on the Google Earth Engine （GEE） platform to evaluate the regional eco-environmental change status， and the impact of the evolution of urban expansion pattern on the change of eco-environmental quality was investigated using a geographically and temporally weighted regression model （GTWR）. The study produced several interesting results： ① The overall expansion rate of urban land in the BTH urban agglomeration from 2000 to 2020 was 217.22 km·a， and the expansion rate from 2000 to 2010 was faster than the rate from 2010 to 2020. Among regions， the urban expansion rate was slower in the northwestern mountains and higher in the southeastern plains. The overall expansion intensity of the BTH urban agglomeration during the study period was 6.14%. Areas with high-speed expansion， rapid expansion， and medium-speed expansion were mainly concentrated in the southeastern plains， and areas with low-speed expansion and slow expansion were mainly located in the northwestern part of the study area. During the study period， the number of urban agglomerations in BTH， the density of patches， and the landscape shape index showed increasing trends， the maximum patch index showed a decreasing trend， and the fragmentation of urban land was increasing. ② During the period from 2000 to 2020， the IRSEI of the BTH urban agglomeration as a whole showed an upward trend. In 2020， the IRSEI had increased by 6.13% compared with the early stage of the study， and the ecological environment quality of the Yanshan Mountain area in the north and the Taihang Mountain area in the west was higher， while that of the Bashang Plateau area and the southeastern plains area was poorer. During the study period， the ecological environment quality decreased mainly in the peripheral area along the Bohai Sea and the Southeast Plain area， especially in and around the urban centers， while the ecological environment quality increased mainly in the western Taihang Mountain area and the northern Yanshan Mountain area. ③ The degree of influence of urban expansion on the changes of ecological environment quality revealed obvious spatial differentiation， and the regression coefficient of landscape shape index was negative in most counties and regions， which is the main reason for the changes of ecological environment quality. Urban expansion has mainly negative impacts on the ecological environment quality in the region， and reasonable development policies should be formulated to harmonize urban development with ecological environment protection.