1. Introduction The Loess Plateau in northern China is located in the catchment of the middle reaches of the Yellow River; it covers an area of 640,000 km2 (Figure 1a) [1], and, in typical areas, it has a depth of more than 300 m [2,3]. The land use classification includes farmland, forestland, grassland, and desert (Figure 1b) [4]. The average annual precipitation varies from 750 mm in the southeast to 200 mm in the northwest, with 70% in the growing season between May and September.
