## 2 Methodology  
### Study Area  
Previous empirical studies indicate that from 2006 to 2013, there was an N-shaped relationship between urbanization and ecological efficiency, and other studies show that from 2008 to 2017 [37], ecological efficiency slightly declined along with China's urbanization [38], while the current new-type urbanization in China (Refer to \"The National New-type Urbanization Plan (2014-2020)\" from National Development and Reform Commission of China: [[https://www.ndrc.gov.cn/xwdt/ztzl/xxczhjs/ghzc/201605/t20160](https://www.ndrc.gov.cn/xwdt/ztzl/xxczhjs/ghzc/201605/t20160)]([https://www.ndrc.gov.cn/xwdt/ztzl/xxczhjs/ghzc/201605/t20160](https://www.ndrc.gov.cn/xwdt/ztzl/xxczhjs/ghzc/201605/t20160)) 505_971882.html?code=&state=123 (accessed on 30 April 2022)) that emphasizes the improvement of ecological environment, has yielded good ecological outcomes in pollution reduction and energy efficiency increase [39]. This study explores the ecological consequence of urbanization in China. Specifically, we selected the Beijing-Tianjin-Hebei Urban Agglomeration (BTHUA) region in China as the case study area to empirically assess ecological resilience and its influencing factors (Figure 1). The research was conducted on a 1 km \(\times\) 1 km grid scale to observe fine-scale variation of urban ecological resilience change, and the research period is set from 2000-2020 to observe the rapid urbanization in China in the last twenty years and its ecological impacts.  
The BTHUA region, also known as the Capital Economic Circle, is one of the major urban agglomerations in China, with high levels of urbanization and industrialization, though it suffers from ecological and environmental problems such as water resource shortage, air pollution, extensive land use and forest degradation, urban floods, and heatwave, etc. This region is semi-arid and semi-humid, has a temperate and warm temperate continental monsoon climate with an average temperature of 1 \({}^{\circ}\)C to 15 \({}^{\circ}\)C, abundant light, uneven spatial distribution of annual precipitation (about 300 mm to 750 mm from west to east), and the average annual evaporation is generally 900 mm to 1000 mm. The region is divided into plateau, mountain hills, basin and plain from northwest to southeast.  
Currently, under the national policy of \"Coordinated Development of the Beijing-Tianjin-Hebei Region\", the overall positioning of the BTHUA region is \"a world-class city cluster with the capital as the core, a new engine for economic growth driven by innovation and coordinated development, and a demonstration area for ecological restoration and environmental improvement\" (Source: Outline of Coordinated Development of the Beijing-Tianjin-Hebei Region issued by State Council in 2015). Now, this region is still in the middle of industrialization and undergoing rapid urbanization and is also the main area of population inflow. In 2021, the permanent resident population rate in Beijing, Tianjin and Hebei were 87.5%, 84.88% and 61.14%, respectively (Data source: [[https://data.cnki.net/](https://data.cnki.net/)]([https://data.cnki.net/](https://data.cnki.net/)), accessed on 15 May 2022). In the future, this region will continue to host population inflow, with the ecological environment pressure, the contradiction of space resources utilization and the lack of regional infrastructure caused by urbanization expected to be more prominent [39].