## 4 Results  
### Spatial and Temporal Variation of EQI  
During the growing season of 2000-2020, the EQI values in Anhui province ranged from 62.47 to 74.93, with a multi-year average of 71.82 (Figure 3). The results indicate a statistically significant increasing trend with an annual growth rate of 0.61%. The trend of the EQI time series was determined using the Mann-Kendall (MK) test and the sliding \(t\)-test (Figure 4). The MK test revealed two cross-points in the curves of UF and UB in 2004 and 2005, respectively, with a significant confidence interval of 0.05. However, the t-statistic of EQI in the sliding \(t\)-Test did not exceed the significance level of 0.05. By combining both methods, we determined that EQI has significantly increased. Nevertheless, no mutation point could be observed in the EQI time series. From 2000 to 2020, the EQI values in different geographic regions of Anhui province exhibited different degrees of increase (Figure 5). The Jianghuai hills and Huaibei plain had relatively high annual growth rates of 1.49% and 0.91%, respectively, but their interannual fluctuations were large. The ecological quality of vegetation along the river plain was relatively stable, with EQI values fluctuating between 60.58 and 71.83 and an annual growth rate of 0.45%. The Dabie Mountains and Southern Anhui Mountains, which are mainly forested with high vegetation cover, had higher EQI values than other regions and less volatility, with annual growth rates of 0.55% and 0.01%, respectively. The growing season EQI in Anhui Province differed across elevation and slope zones (Figure 6). EQI generally increased with rising elevations when the elevations were less than 600 m, while it decreased gradually with rising elevations when the elevations were greater than 600 m. EQI also increased with rising slope when the slope was between 0 and 18\({}^{\circ}\) but decreased with rising slope when the slope was greater than 18\({}^{\circ}\). Figure 4: (a) Mann–Kendall test for EQI; (b) Sliding \(t\)-test for EQI. Figure 5: Interannual variation in EQI by geographic region in Anhui Province. Figure 3: Interannual variation in EQI during the growing season in Anhui Province, 2000–2020. In terms of spatial distribution, the multi-year EQI in Anhui Province has obvious spatial distribution differences (Figure 7a), showing a trend of \"good in the south, bad in the north, and the worst in the middle\". The EQI in the Dabie and southern Anhui mountains is the highest, with an average EQI value between 80 and 100 and an EQI grade of \"excellent\". EQI in the Huaibei Plain is relatively poor, with EQI grade mostly \"good\" and \" Moderate\". The lowest EQI is distributed in the Hefei city area and the upper Yangtze River basin in the province. Luan, Huainan, Hefei and Maanshan have more fluctuations in EQI over 20 years, while EQI of cities in southern Anhui is more stable (Figure 7b). Figure 6: Relationship of EQI with elevation (**a**) and slope (**b**) in Anhui Province. (**a**) where 1–19 represent the elevation bands 0–100 m 100–200 m... 1700–1800 m, respectively, (**b**) where 1–31 represent slope bands 0–2\({}^{\circ}\), 2–4\({}^{\circ}\), 4–6\({}^{\circ}\), respectively... 36–38\({}^{\circ}\). Figure 7: EQI classes (**a**) and standard deviations (**b**) of growing season in Anhui Province, 2000–2020. From 2000 to 2020, the EQI in most areas of Anhui Province remained basically unchanged, accounting for 52.91%. The area with increase in EQI is much larger than that with decrease. (Figure 8). The regions with very significantly increased and significant increase in EQI account for 30.74% and 12.75% of the land area, respectively, and are mainly located in Huainan, Chuzhou and the northern part of Hefei. The areas with very significantly decreased and significantly decrease in EQI accounted for 2.45% and 1.15%, respectively, and are mainly located in the watershed of the Yangtze River pathway and the central area of Hefei.