In this section, we will quantitatively distinguish the reasons for the change of runoff before and after the abrupt points in nine sub-basins. Table 6 shows the total runoff change (ΔR) in Period II relative to Period I, the meteorological factors (ΔRC) – precipitation (ΔRP) and potential Evapotranspiration (
), and the amount of runoff change caused by human activities (△Rn), and its proportion in the total runoff change. The calculation results show that the runoff of the nine sub-basins during Period II is reduced compared with Period I, and both climate change and human activities in the study area have led to the reduction of runoff. Human activities are the main reasons for the reduction of watershed runoff, but the contribution rate varies. The largest contribution of human activities (△Rn/△R) to runoff can be detected in KY and HF (>90%). The contribution rate of human activities in other watersheds is more than 55% (Table 6, Figure 5). Previous studies have also confirmed that human activities are the main reason for the reduction of runoff in the MRYR (Shi et al. 2012; Kong et al. 2016).
), and the amount of runoff change caused by human activities (△Rn), and its proportion in the total runoff change. The calculation results show that the runoff of the nine sub-basins during Period II is reduced compared with Period I, and both climate change and human activities in the study area have led to the reduction of runoff. Human activities are the main reasons for the reduction of watershed runoff, but the contribution rate varies. The largest contribution of human activities (△Rn/△R) to runoff can be detected in KY and HF (>90%). The contribution rate of human activities in other watersheds is more than 55% (Table 6, Figure 5). Previous studies have also confirmed that human activities are the main reason for the reduction of runoff in the MRYR (Shi et al. 2012; Kong et al. 2016). Table 6
Contribution of climate change and human activities in the study area
| Basin | △R (mm) | △RP (mm) |  (mm) | △RC (mm) | △RC/△R (%) | △Rn (mm) | △Rn/△R (%) |
|---|---|---|---|---|---|---|---|
| HF | −35.6 | −1.5 | −1.3 | −2.8 | 7.6 | −32.9 | 92.4 |
| KY | −41.9 | 8.6 | −10.4 | −1.8 | 4.2 | −40.1 | 95.8 |
| WD | −14.8 | −4.3 | −1.9 | −6.2 | 42.0 | −8.6 | 58.0 |
| YR | −11.6 | −2.7 | −1.4 | −4.1 | 35.3 | −7.5 | 64.7 |
| FR | −25.8 | −12.2 | 1.0 | −11.2 | 43.4 | −14.6 | 56.6 |
| BL | −11.2 | 10.1 | −13.6 | −3.5 | 31.4 | −7.7 | 68.6 |
| JR | −16.0 | −4.7 | −2.5 | −7.2 | 44.9 | −8.8 | 55.1 |
| YL | −69.3 | −28.9 | 5.5 | −23.4 | 33.8 | −45.9 | 66.2 |
| QR | −58.1 | −31.3 | 8.9 | −22.4 | 38.6 | −35.7 | 61.4 |
| Basin | △R (mm) | △RP (mm) | (mm) | △RC (mm) | △RC/△R (%) | △Rn (mm) | △Rn/△R (%) |
|---|---|---|---|---|---|---|---|
| HF | −35.6 | −1.5 | −1.3 | −2.8 | 7.6 | −32.9 | 92.4 |
| KY | −41.9 | 8.6 | −10.4 | −1.8 | 4.2 | −40.1 | 95.8 |
| WD | −14.8 | −4.3 | −1.9 | −6.2 | 42.0 | −8.6 | 58.0 |
| YR | −11.6 | −2.7 | −1.4 | −4.1 | 35.3 | −7.5 | 64.7 |
| FR | −25.8 | −12.2 | 1.0 | −11.2 | 43.4 | −14.6 | 56.6 |
| BL | −11.2 | 10.1 | −13.6 | −3.5 | 31.4 | −7.7 | 68.6 |
| JR | −16.0 | −4.7 | −2.5 | −7.2 | 44.9 | −8.8 | 55.1 |
| YL | −69.3 | −28.9 | 5.5 | −23.4 | 33.8 | −45.9 | 66.2 |
| QR | −58.1 | −31.3 | 8.9 | −22.4 | 38.6 | −35.7 | 61.4 |
Note: The change of runoff is negative, indicating that the runoff in Period II is less than in Period I. The runoff change is positive, indicating that the runoff in Period II is increased compared with Period I.
Table 7
Multi-year average and growth rate of NDVI in nine sub-basins
| Basin | Annual average | Growth rate (%) |
|---|---|---|
| HF | 0.21 | 21.6 |
| KY | 0.21 | 25.2 |
| WD | 0.21 | 27.3 |
| YR | 0.28 | 36.8 |
| FR | 0.34 | 13.7 |
| BL | 0.37 | 20.1 |
| JR | 0.31 | 19.1 |
| YL | 0.42 | 14.9 |
| QR | 0.39 | 15.8 |
| Basin | Annual average | Growth rate (%) |
|---|---|---|
| HF | 0.21 | 21.6 |
| KY | 0.21 | 25.2 |
| WD | 0.21 | 27.3 |
| YR | 0.28 | 36.8 |
| FR | 0.34 | 13.7 |
| BL | 0.37 | 20.1 |
| JR | 0.31 | 19.1 |
| YL | 0.42 | 14.9 |
| QR | 0.39 | 15.8 |
Figure 5
Spatial distribution of the contribution of human activities to runoff.