## 3 Results  
### LULC Changes in the Research Area from 2001 to 2020  
In 2020, the distribution of land use types varied, with grassland (46.31%) and unutilized land (23.72%) comprising the largest areas, followed by cultivated land (15.40%) and forest (11.29%). Water bodies (1.37%) and constructed land (1.56%) accounted for the smallest proportions (Figure 4). Grassland dominated land use types across regions, except for the NWC, NEC, and EC regions. The NWC region had the highest percentage of unutilized land (57.20%), while the EC and NEC regions had the highest percentages of cultivated land, at 54.86% and 44.21%, respectively. Regions with forest cover exceeding 20% included NEC (28.07%), SEC (24.25%), and SC (28.20%), which are recognized as significant forested areas in China. The NEC region had the highest proportions of water bodies (5.53%) and constructed land (8.41%). With the exception of NWC (57.20%), NC (17.94%), and QT (34.06%), unutilized land ratios in other regions were below 1%.  
Our analysis of LULC on a yearly basis in China indicated that the majority of pixels, accounting for 84.77%, experienced no change over time. Conversely, the rates of single, double, and triple changes were 8.28%, 4.31%, and 1.64%, respectively. With the exception of grassland and unutilized land, the land area of other categories expanded in 2001-2020 in China (Figure 5). Cultivated land, forest, water bodies, and constructed land exhibited growth rates of 0.16 \(\times\) 10\({}^{4}\) km\({}^{2}\cdot\)a\({}^{-1}\), 1.05 \(\times\) 10\({}^{4}\) km\({}^{2}\cdot\)a\({}^{-1}\), 0.13 \(\times\) 10\({}^{4}\) km\({}^{2}\cdot\)a\({}^{-1}\), and 0.15 \(\times\) 10\({}^{4}\) km\({}^{2}\cdot\)a\({}^{-1}\), respectively. Conversely, the areas of grassland and unutilized land decreased at rates of -0.96 \(\times\) 10\({}^{4}\) km\({}^{2}\cdot\)a\({}^{-1}\) and -0.52 \(\times\) 10\({}^{4}\) km\({}^{2}\cdot\)a\({}^{-1}\), respectively.  
Figure 4: Rate of LULC change in China and its various regions in 2020.  
During the period from 2001 to 2020, there were significant changes in land use patterns across various categories, as illustrated in Figure 6. There was a consistent growth in construction land without any corresponding decrease, indicating the ongoing urbanization in China. The shifts in land area primarily occurred in transitions between grassland and cultivated land, as well as forest areas. Conversely, there were minimal changes observed in water bodies and constructed land. The LULC is closely linked to national policies, particularly those focused on reforestation and converting cultivated land to promote the expansion of grassland and forest. An obvious transition was observed between grassland and unutilized land, where grassland was either degraded to unutilized land due to climate change and human activities, or unutilized land was transformed into grassland as part of ecological restoration efforts to harness the resource potential of unutilized land in the context of climate change. It is important to note that, except for the conversion of other land types to constructed land (coded 15, 25, 35, 45, and 65), which decreased after 2016, the area of other LUTs has shown a relatively significant increase.  
Figure 5: Area changes in various LUTs in China in 2001–2020.