## 4 Discussion  
### The Resilience of the BTHUA  
This study reveals that urban resilience in the BTHUA has trended upward since 2010, a pattern consistent with recent resilience research on UAs in China [43, 45]. Such consistency is deeply rooted in China's sustained efforts to advance urban resilience practices. The robust urban resilience has enhanced governance capabilities at the UA scale, thereby more effectively facilitating the BTHUA in achieving efficient governance and realizing ecologically friendly development. From the perspective of subsystems, ScoR showed the highest growth rate, and this finding is consistent with the conclusions of other studies conducted in the BTHUA [25, 42]. This rapid increase was primarily driven by economic expansion, improvements in social services, and the integrated development of urban and rural areas, all of which can be activated and enhanced through the implementation of targeted policies and coordinated collaborative efforts. TecR has been enhanced by continuous innovation and new technology applications, which help to update urban management concepts and strategies to address the misalignment between social development and ecosystem protection. Previous studies have demonstrated the promoting effect of sound infrastructure on urban resilience but overlooked the contributions of innovation capacity and technical efficiency, which may have led to underestimations of urban resilience levels. Also, TecR still requires deeper support from the social system, as its improvement has lagged behind that of SocR, which can be attributed to social factors such as policy orientation, institutional barriers, social equity issues, and public participation [70]. The enhancement of EcoR can be attributed to regional ecological restoration projects and resource conservation practices, yet its growth rate remains the lowest. This is primarily because the complex dynamics and threshold effects of ecosystems have made enhancing the key variables for maintaining ecosystem services a time-consuming process. Moreover, increasing urbanization pressure, compounded, and water resource constraints have further constrained EcoR enhancement. Figure 10: The obstacle degree of various obstacle factors across cities in the BTHUA for (**a**) 2010 and (**b**) 2022. Urban resilience relies on multifaceted interactions and feedback among the components of urban subsystems, which manifest in diverse forms across urban areas. Studies on the BTHUA have shown that over the past decade, its economic-social and eco-environmental subsystems have achieved coupled and coordinated development, while disparities in the CCD among cities remain prominent [71; 72]. Driven by the collective enhancement and mutual reinforcement of ScoR, EcoR and TecR, the CCD of all cities within the region has been improved. The region has shifted towards a sustainable development model that emphasizes the integration of social, ecological, and technological subsystems, rather than focusing solely on the welfare of the social subsystem. However, technological innovation and environmental improvement are not inherently positive. Without proper consideration of its wider inequalities and vulnerabilities, they can reinforce existing patterns of exclusion and even create new ones for disadvantaged groups [49]. The continuous growth in both the quantity and intensity of the spatial connections among cities in the BTHUA has demonstrated that intercity communication and cooperation within the region have become increasingly close. In particular, cities in the BTHUA have become more intricately connected through infrastructure, ecosystems, and socioeconomic systems, enabling the sharing of development strategies, resources, and technologies to enhance resilience. With key cities exerting spillover effects and regional integration advancing, an increasingly stable regional network and strong sub-regional linkages have emerged, making urban agglomerations more resilient.