## 3 Results
### Spatiotemporal Changes of LCE  
As shown in Figure 4, the LCE in the study area showed a significantly increasing trend from 2000 to 2019 (1.76 million t; \(p<0.01\)). Specifically, the average value of LCE in this period was 31.30 million t; the total amount of LCE in 2000 was 13.58 million t; LCE increased to 31.02 million t in 2009; and the total amount of LCE reached 43.66 million t in 2019. From 2000 to 2009, the growth rate of LCE was relatively fast, but the growth rate showed a significant downward trend from 2010 to 2019. This change may serve as a great sign in terms of China's emission reduction goals and the tasks established at the 2009 Copenhagen Conference and the 2015 Paris Climate Conference. In addition, we found that grassland, forestland, and wetland all showed negative carbon emissions (Figure 5), indicating that these land types had an important carbon absorption role, therefore showing carbon sink. In general, the carbon absorption of these three land use types showed a significant downward trend from 2000 to 2019. By contrast, cropland and construction land were mainly characterized by positive carbon emissions. In terms of inter-annual changes, carbon emissions from cropland showed an obvious increase trend from 2000 to 2013 and then indicated a downward trend, wh \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**2019******[**2000**]** & **Cropland** & **Forestland** & **Grassland** & **Wetland** & **Construction** & **Water** & **Unused** & **Total in** & **Transfer** \\ \hline Cropland & 33,275.07 & 30.51 & 48.96 & 0 & 0 & 0 & 0 & 33,354.54 & 79.47 \\ \hline Forestland & 84.6 & 23,160.6 & 105.57 & 0 & 0 & 0 & 0 & 23,350.77 & 190.17 \\ \hline Grassland & 99.27 & 209.52 & 3696.84 & 0.18 & 0 & 0 & 0 & 4005.81 & 308.97 \\ \hline Wetland & 0 & 0 & 0 & 93.78 & 0 & 0 & 0 & 93.78 & 0 \\ \hline Construction land & 2218.05 & 1.62 & 101.43 & 2.88 & 440.19 & 0.99 & 1.26 & 2766.42 & 2326.23 \\ \hline Water & 0 & 0 & 0 & 0 & 0 & 104.58 & 0 & 104.58 & 0 \\ \hline Total in 2000 & 35,676.99 & 23,402.25 & 3952.8 & 96.84 & 440.19 & 105.57 & 1.26 & 63675.9 \\ \hline Transfer out in 2000 & 2401.92 & 241.65 & 255.96 & 3.06 & 0 & 0.99 & 1.26 & \\ \hline \end{tabular}
\end{table} 
Table 4: Transfer matrix of land use in the GZA from 2000 to 2019 (km\({}^{2}\)). Figure 4: The temporal variations of LCE in the GZA from 2000 to 2019.  
conversion of large amounts of cropland area to construction land. Meanwhile, the carbon emissions in the construction land showed a significant increase trend (0.54 million t/a; \(p<0.01\)). These indicate that the increase of carbon emissions in the GZA in the past two decades has mainly been due to the increasing energy consumption and human-related carbon emissions encouraged in the process of urbanization. Based on the natural break point method, the land-use carbon emissions from 2000 to 2019 were divided into four types: high land-use carbon emissions, moderate land-use carbon emissions, low land-use carbon emissions, and negative land-use carbon emissions (Figure 6), and then the change characteristics of different types of land carbon emissions were analyzed. Specifically, the regions with high land-use carbon emission levels accounted for about 3-5% of the total area, showing an upward trend (from 0.77% in 2000 to 5.45% in 2019). These areas were mainly distributed in the Xi'an and Xianyang urban areas, which may have been caused by the acceleration of urbanization and the intensification of energy consumption. The regions with moderate land-use carbon emission grade occupied nearly 33% of the total area, indicating a decreasing trend overall (from 35.96% in 2000 to 29.82% in 2019). These areas were mainly observed in the cropland distribution areas of Guanzhong, indicating that the improvement of agricultural farming methods has promoted the reduction of carbon emissions in recent years. The regions with low land-use carbon emission grade accounted for about 16% of the total coverage area and also showed a downward trend (from 17.76% in 2000 to 14.81% in 2019).