## 4 Discussion
### The Effect of Urbanization on Grassland Conversion out from 2000 to 2020  
This study shows that urbanization-related driving factors were the primary drivers of GCO in the HBO region during both research periods (2000-2020). Notably, in Hohhot, the key driving factors include HH, WC, TKT, QSH, and HL; in Baotou, BT and TMY; in Ordos, DS. Overall, the impact of urbanization in the western part of the region is significantly greater than in the eastern part, reflecting spatial imbalances (see Figures 7 and 8). This difference is mainly attributed to the rapid urbanization in the eastern region and the marked acceleration of population concentration (Figure S5). Population migration is one of the core drivers of urbanization, and as an important economic center of Inner Mongolia, the HBO region's rapid urbanization is closely linked to the migration of populations from rural areas to cities. Notably, during the period from 2000 to 2020, a large number of rural residents migrated to cities such as Hohhot, Baotou, and Ordos, driving the expansion of urban areas and the rapid growth of urban land. Figure S5a indicates that between 2000 and 2020, the urban population in the study area consistently exceeded the rural population, and the gap between them gradually widened. The urban populations in Hohhot and Baotou were greater than those in Ordos. During this period, urban construction land and rural settlements in the study area increased by 332 km\({}^{2}\) and 102 km\({}^{2}\), respectively, significantly changing the use of grassland resources. These changes were particularly evident in the development of wide roads, large squares, new urban areas, and the encroachment of expanding industrial and mining land. This unplanned expansion directly occupied grasslands, destroyed surface vegetation and the ecological environment and led to a significant increase in the intensity of GCO. Previous studies have shown that the construction land area in the study area exhibits the characteristics of disorderly expansion, especially with the excessive pursuit of wide roads, large squares, new urban areas, and industrial and mining land, resulting in changes to the surface landscape pattern and the ecological environment, destroying natural vegetation, and weakening the stability of the land structure [61].  
HBO is a resource-based region dominated by industry and mining, and the expansion of industrial and mining land has had a significant negative impact on the grassland ecosystem. Since 2000, the study area has gained 1270 km\({}^{2}\) of industrial and mining land, and mining activities have combined the direct occupation and indirect destruction of grasslands, further exacerbating the loss of grassland resources [62]. Industrial and mining development not only leads to a reduction in grasslands [63] but also triggers habitat fragmentation [64], soil erosion, and pollution [65]. These destructive activities have weakened the ecological functions of grasslands, such as carbon sequestration, water conservation, and the maintenance of biodiversity [66]. Furthermore, the expansion of mining sites is accompanied by the construction of roads, with a total increase of 6606 km in road length. These roads directly occupy grasslands and, by facilitating human activities in the surrounding areas, such as agricultural expansion [67], industrial development, and tourism [68], further exacerbate grassland degradation [69].