2.1 Study area
The area targeted by this research is the Zhangbei County in the Hebei Province, China (Figure 1; 40°03′ to 41°27′N, 114°20′ to 114°58′E). The study area has a mid-temperate continental monsoon climate, with an altitude ranging between 1600 m and 1800 m, an annual average temperature of 3.2 °C, and an annual precipitation of approximately 300 mm. Relatively dry conditions have caused vegetation degradation in this area (Sun et al., 2019). The study area has good wind resources and is the main route through which the northwest monsoon goes south in winter and spring. The annual average wind speed is approximately 6 m/s. In average, there are 30 days in a year with wind speeds exceeding the Near Gale (from international wind scale). The Zhangbei County belongs to the typical agro-pastoral transition zone. The soil conservation measures of the farmland are not perfect, which lead to soil wind erosion occasionally.
Figure.1 Location of the study area. The gray is the Hebei Province; the purple region is Zhangbei County; and the red star is Beijing.