## 4 Results
### Spatial Variation of the EE from 2002-2022  
#### 4.2.1 Local Spatial Variation in the EE in the Study Area  
Although there has been an overall improvement in the EE since 2002, the local changes in the study area remain unclear [52]. To better understand the spatial characteristics of regional EE changes in different regions (that is, the coal mining region, the GGP region, and the urbanization region) under the influence of human projects, RESI from 2002-2022 was analyzed. Figure 8 shows the variation in different land use types in 2002 and 2022. It is evident that the area of the GGP region (e.g., B1, B2, and B3) and the urbanization region (A) has significantly increased in the last 20 years, while the area of arable land has decreased. However, changes in land use types in the Huanglong coal base are difficult to distinguish directly. Further analysis on this area is presented below. Taking the Dafosi coal mine in the Huanglong coal base as an example (as shown in Figure 9), we analyze the influence of coal mining activity on the local EE. The Dafosi coal mine is located in a loess hilly-guilly region, with a mining area of about 70 km\({}^{2}\) and a total coal reserve of 765 Mt. Coal mining activity began in 2007, with a designed annual coal mining capacity of 8 million tons and a service life of 70 years [3; 53]. The distribution of the annual mining workings of the Dafosi coal mine is shown in Figure 9.  
After underground coal mining, a large-scale subsidence basin with a maximum subsidence value of more than 7 m will form on the ground. As shown in Figure 2, this will lead to serious damage to land resources and construction facilities and further cause environmental damage, such as soil erosion, lowering of the groundwater level, and vegetation withering [54]. The area of the coal mining region and surface subsidence region of the Dafosi coal mine from 2007 to 2022 is shown in Table 4 [55]. To quantitatively analyze the influence of subsidence on the surrounding EE in the Dafosi coal mine, the surface subsidence region was considered as the direct impact area of coal mining, and the indirect impact area (called the buffer area) was expanded by 3 km outward. The area to the east of the buffer area, which had not yet been affected by coal mining and had similar geographic conditions, was taken as the comparison area. The location of these three areas can be found in Figure 10. The RSEI values for the three areas were calculated from 2002-2022 and compared, as shown in Figure 11. Statistical analysis of the RSEI values of the three areas shows that the RSEI of the direct impact area of coal mining in the Dafosi mine has a high correlation with the RSEI of the buffer area and the comparison area, with correlation coefficients of 0.967 and 0.941, respectively. This means that the RSEI values of the direct impact area, buffer area, and comparison area are highly correlated, and the trend of all three is consistent, with an overall increasing trend. However, in the vast majority of years, the annual average RSEI in the direct impact area is smaller than that in the buffer area, while the annual average RSEI in the buffer area is smaller than that in the comparison area. After the Dafosi coal mine started mining in 2007, the annual average RSEI value in the direct impact area was 0.552, the annual average RSEI value in the buffer area was 0.576, and the annual average RSEI value in the comparison area was 0.596. The annual average RSEI value in the direct impact area was 4.1% lower than that in the buffer area and 7.3% lower than that in the comparison area. Further analysis shows that the difference between the RSEI values of the three areas was very small and remained almost equal during the period 2002-2006. This indicates that before coal mining began in 2007, the EE quality of the three regions was almost the same.