**3. Results**

## *3.1. Watershed of Terrace Unit and Vegetation Unit*

The terrace ratio is the proportion of terrace area to water and soil loss area [78]. In 2012, the total terrace area of Pianguanhe was 189.32 km2, accounting for 9.87% of the whole basin and giving a terrace ratio of 10.18%. The terrace ratio of Pianguanhe was 1.80% in 1979 [50]. In view of data availability, we chose terrace data from 2012 (to represent the 2010s) and extracted its terrace watershed. The terrace watershed was 169.90 km2 in 2012. The terrace control area is the sum of terrace area and terrace watershed and accounted for 1.89 times the area of the terrace, as shown in Figure 6a.

**Figure 6.** Extraction of terrace watershed (**a**) and vegetation watershed (**b**) of Pianguanhe in 2010s.

The area of forestland and grassland in Pianguanhe was 1328.70 km<sup>2</sup> in 1980s and 1349.17 km2 in the 2010s, giving an increase of 20.47 km2. The average vegetation coverage was 22.27% in 1980s and 62.74% in the 2010s, giving an increase of 40.47%. Thus, the vegetation quality demonstrated a significant increase compared to the area. We extracted the vegetation watersheds in the 1980s and 2010s. Figure 6b shows the vegetation watershed of Pianguanhe in the 2010s. Vegetation control area was the sum of vegetation units and vegetation watershed. It was 1675.77 km2 in the 1980s and 1693.96 km<sup>2</sup> in the 2010s, indicating that it did not change very much.
