## 2 Materials and Methods  
### Study Area  
Representing regions marked by the most significant contradictions between economic development and ecological protection, the urban agglomerations of Beijing-Tianjin-Hebei (BTH), the Yangtze River Delta (YRD), and the Pearl River Delta (PRD) have consistently garnered considerable attention and concern. The spatial location and land cover information for the three urban agglomerations in 2020 can be seen in Figure 1.  
BTH is the largest urban agglomeration in northern China, contributing 8.3% to the total GDP of the country. Encompassing an expansive area of approximately 216,800 km\({}^{2}\) (113\({}^{\circ}\)04\({}^{\prime}\)-119\({}^{\circ}\)53\({}^{\prime}\)E, 36\({}^{\circ}\)01\({}^{\prime}\)-42\({}^{\circ}\)37\({}^{\prime}\)N), it provides resources to sustain a population of approximately 110 million people [33]. CYRD comprises 27 cities in the core region of YRD, adjusted according to the Outline of the Yangtze River Delta Regional Integrated Development Plan (refer to Table S1). In comparison to BTH, CYRD covers a larger area of 225,000 km\({}^{2}\) (115\({}^{\circ}\)45\({}^{\prime}\)-122\({}^{\circ}\)57\({}^{\prime}\)E, 29\({}^{\circ}\)34\({}^{\prime}\)-34\({}^{\circ}\)29\({}^{\prime}\)N), accommodating over 160 million people and contributing 20% to the country's total GDP [34]. The Pearl River Delta (PRD) covers a smaller area of 50,000 km\({}^{2}\) (111\({}^{\circ}\)21\({}^{\prime}\)-115\({}^{\circ}\)25\({}^{\prime}\)E, 29\({}^{\circ}\)34\({}^{\prime}\)-24\({}^{\circ}\)24\({}^{\prime}\)N) but supports approximately 86 million residents, contributing about 11% to the total GDP of China. PRD boasts the highest urbanization rate among the three major urban agglomerations at 86%, followed by CYRD at 75%, while BTH has an urbanization rate of 66.7% [35]. In terms of natural conditions, BTH experiences a typical temperate monsoon climate, characterized by average annual temperatures ranging between 10-12 \({}^{\circ}\)C and cumulative average annual precipitation between 350-700 mm [36]. On the other hand, CYRD and PRD both feature a subtropical monsoon climate, marked by simultaneous rain and heat in the summer and average temperatures above 0 \({}^{\circ}\)C during the coldest winter months. The distinction between the two areas lies in PRD's more abundant rainfall and elevated temperatures. Figure 1: Spatial location and land cover (LC) information in 2020 of study area. (**a**) Location of three major urban agglomeration in China; (**b–d**) LC information of BTH, CYRD, and PRD, respectively, in 2020. The land cover information was extracted from the China Land Cover Dataset (CLCD) which can be obtained from the link at Data Availability Statement section. Significant distinctions in ecological threats and factors influencing ecological quality changes exist among the three urban agglomerations. The BTH region has witnessed continuous deterioration in ecological quality due to massive resource consumption and the prolonged development of heavy industry. The ecological threat, primarily manifested as severe air pollution, has consistently impacted human well-being, reaching a critical point in 2013 when air pollution levels accounted for one-third of the national total [37]. Policies related to ecological protection and urban expansion characterized by rapid land transitions have contributed to variations in ecological quality between the southeast and northwest regions of BTH [38]. CYRD has faced heightened human-land pressure and significant urban expansion in recent decades. Frequent human-driven landscape reconstruction has increased the complexity of the landscape structure and exacerbated ecosystem fragility. Additionally, the dense population's substantial demand for thermal power generation has resulted in severe air pollution and frequent occurrences of acid rain [39]. Urban land expansion, aquaculture, and farmland occupation are pivotal factors contributing to the degradation of ecological quality in CYRD [29].