## 2 Study Area  
Wuhan, the capital city of Hubei Province in central China, is a prime example of rapid urbanization and vertical growth. Strategically located at the confluence of the Yangtze and Han rivers, the city has evolved into a major economic, educational, and technological hub.  
As of 2020, it is home to approximately 12.44 million people, making it the ninth-largest city in China [32; 33; 34].  
The rapid urban growth in Wuhan has led to significant urban expansion and land use changes. Studies have shown that the city's arable land area decreased by 78,322.4 km\({}^{2}\) while the built-up land area increased by 52,559.28 km\({}^{2}\) in the last three decades. This expansion has resulted in the loss of agricultural land and green spaces, leading to concerns about environmental sustainability [35].  
From 2012 to 2020 (i.e., the period monitored in this research using satellite X-band SAR data), Wuhan experienced significant transformations: its GDP grew from 775.22 billion yuan to 1561.61 billion yuan, and its population increased by 23%, from about 10.12 million to 12.44 million. These changes were driven by initiatives such as the \"Rise of Central China\", which focused on enhancing infrastructure and fostering key industries [33; 34].  
This era of accelerated development was marked by extensive urban infrastructure enhancement and a boom in high-rise construction. The city's skyline transformation, exemplified by projects like the Wuhan Greenland Center, reflects a shift towards denser VUG. These developments are crucial for accommodating an expanding population and diversifying economic activities while managing urban land resources efficiently.  
Global datasets are essential for analyzing urban expansion. The GHSL's Settlement Characteristics dataset, with its 10-m resolution, is particularly valuable. Derived from Sentinel-2 2018 composites and other GHS R2023A data, it provides a detailed view of urban landscapes. The 2018 reference data were chosen as an independent comparison dataset for this study [36].  
Managed by the European Commission's Joint Research Centre (JRC), this dataset provides a comprehensive view of settlement patterns, building types, and height classes across various geographical locations.  
Figure 1 presents a comprehensive visualization of Wuhan, a central metropolis within China's Hubei Province, depicted through three distinct panels. The top left panel situates Hubei within the broader context of China, highlighting its national significance. The bottom left panel delineates the city of Wuhan, marked in a striking light blue color, related to its surrounding provincial areas in blue. The GHSL map, positioned on the right side of Figure 1, categorizes Wuhan's buildings into five height classes ranging from less than 3 to over 30 m.  
With regard to the year 2018, the map highlights a notable concentration of tall buildings exceeding 30 m primarily in the Jianghan District, located northwest of the Yangtze River. This area, characterized by its high-rise structures, contrasts sharply with other districts like Wuchang and Hongshan, where the skyline is more diverse, featuring a mix of shorter buildings interspersed with taller structures. Additionally, the peripheral areas of Wuhan predominantly feature buildings shorter than 15 m, illustrating a gradient of urban density that diminishes with distance from the city center.