4.2.2 Soil water changes in the sub–basins
The simulation results of soil water in the Qinhe River Basin exhibited decreasing trends for the two change periods, which can be primarily attributed to the continuous decrease in precipitation. However, the ratio of soil water to precipitation has shown a continuous upward trend. Specifically, the S/P (Soil Water/Precipitation) of the entire basin increased from 0.22 to 0.24, and the S/P average of the sub-basins where the reservoir is located increased from 0.22 to 0.25. These findings indicate that the water conservation capacity of the entire basin has improved, and the water conservation capacity of the sub-basins where the reservoir is located is better.
Interestingly, in the last 30 years of the 20th century, despite the continuous reduction in precipitation, the change in soil water was relatively small, mainly due to the improved vegetation in the basin, which is associated with water and soil conservation measures. The utilization of soil water by plants promotes stability. However, this also demonstrates that the vegetation-carrying capacity of the basin reached a stable state in the 21st century.
Overall, these results reveal that the implementation of water and soil conservation measures, including water conservancy projects, in the Qinhe River Basin has positively impacted its ecology. The simulation results of soil water in a typical sub-basin hosting a reservoir are shown in Figure 6. The study highlights the importance of water and soil conservation measures in the Qinhe River Basin and their positive impact on its ecology. Specifically, the basin’s water conservation capacity has improved, and its vegetation-carrying capacity has reached a stable state in the 21st century. These findings underscore the significance of sustainable water and soil management practices in maintaining the health of river basins.