## 5 Conclusions  
This study constructs a \"Function-Interaction-Pressure-Stability\" (FIPS) index system to assess the ecological quality changes in three major urban agglomerations in China. Combing AHP and PCA methods to determine the indicator weights, we constructed the Ecological Quality Index (EQI) based on a linear model, leading to the following conclusions:  
(1) From 2001 to 2020, the EQI status of the three urban agglomerations changed significantly, with the overall EQI of BTH and CYRD decreasing and the EQI of PRD increasing. Ecological degradation occurred mainly in flat agricultural areas, areas with sufficient water and around economic centers, such as the southeastern part of BTH, the Yangtze River, and Shanghai neighborhoods. CYRD had the largest proportion of ecologically deteriorated areas. (2) Comparing the ecological quality and land cover changes in the core and expansion areas of urbanization, we found that PRD has the largest share of the core area (about 9.9%) and the expansion area of the CYRD occupies the largest share of the area (252.9%). Ecological deterioration was more severe in the expansion areas, so the percentage of ecological deterioration of all land area of BTH and CYRD reaches 60%. Additionally, the location of pixels where ecological deterioration occurs is highly consistent with the location of the new impervious surface due to urbanization LC transfer. Therefore, the main reason for the deterioration of ecological quality is the change of LC. (3) From the analysis results of the EQI and the Urban Synergistic Index (USI), we found that most cities have witnessed ecological deterioration because of the rapid urbanization. The patterns of EQI in all cities of BTH are the most discrete and unbalanced. However, many cities are concentrated in locations where USI is small in absolute value, especially cities in CYRD, meaning the intensity of ecological deterioration is maintained at a low level compared to the high intensity of urban expansion. Furthermore, some citiesfrom BTH, such as Tangshan and Qinhuangdao, should pay more attention to balancing economic growth and ecological protection. **Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/rs16010045/s1](https://www.mdpi.com/article/10.3390/rs16010045/s1)]([https://www.mdpi.com/article/10.3390/rs16010045/s1](https://www.mdpi.com/article/10.3390/rs16010045/s1)), Table S1: Lists of cities of BTH, CYRD and PRD. (UA refers to urban agglomeration); Table S2: Area and occupancy rate of EQI at various levels in core and expansion areas in 2001 and 2020 in three urban agglomerations; Table S3: Result of intensity of urban expansion, EQI changes and USI of all cities in three urban agglomerations. (UEI, EQICI and USI mean the urban expansion intensity, EQI change intensity and urban synergistic index, respectively); Table S4: Total area and land occupation rate of \(\Delta\)EQI at various levels of urban agglomerations; Table S5: Results of collinearity diagnosis of single urban agglomeration; Table S6: Global Moran' I measurement results of EQI in three urban agglomerations. **Author Contributions:** Conceptualization, Y.G., X.Z. and H.W. ; methodology, Y.G. ; data processing, Y.G. and S.Z. ; validation, Y.G., S.Z. and W.S. ; resources, X.Z. ; data curation, Y.G. and S.Z. ; writing--original draft preparation, Y.G. and S.Z. ; writing--review and editing, Y.G. and X.Z. ; visualization, W.S. and S.Z. ; supervision, X.Z. and H.W. ; funding acquisition, X.Z., Y.G. and S.Z. are co-first authors and contributed equally to this work. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was supported and funded by the National Key Research and Development Program of China (Grant No. 2021 YFB3901105), the Open Research Program of the International Research Center of Big Data for Sustainable Development Goals (Grant No. CBAS20220 RP01), the National Natural Science Foundation of China (Grant No.