The Loess Plateau is located in the middle reaches of the Yellow River basin, north China (Fig. 1), and lies roughly within 100°54′–114°33′ E and 33°43′–41°16′ N. The Plateau covers an area of more than 600,000 km2 , extending to the Yinshan Mountains in the north, the Qingling Mountains in the south, the Wuqiaoling–Riyue Mountains in the west and the Taihang Mountains in the east. Most of the Plateau has sub-humid and semi-arid climates, with an average annual temperature of 4.3 °C in the northwest and 14.3 °C in the southeast.
The average annual precipitation ranges from 200 mm in the northwest to 750 mm in the southeast and mostly falls as high intensity rainstorms (Li et al., 2009). The Plateau surface is covered by highly erodible loess layers averaging 100 m deep. The surface soil types vary from northwest to southeast in the order of Eolian sand, sandy loess, typical loess and clayey loess (Liu, 1964). In the same direction, the natural vegetation types vary from arid desert to steppe and then to broad-leaf deciduous forest (Yang and Yuan, 1991). The major crops are wheat, corn, millet, sorghum, soybean, and buckwheat