Effects of land-use pattern change on soil and water loss at the catchment scale in the hilly and gully area of the loess plateau of China

The hilly and gully area of the Loess Plateau of China suffers some of the highest soil erosion rates on the Earth, and one of the most important reasons is irrational land-use. The study on the effects of land-use pattern on soil and water loss is helpful not only to the comprehensive watershed management but also to further understanding of landscape pattern and ecological process. A case study was carried out in Xinghe catchment of the Loess Plateau, and DEM, land use maps, rainfall and hydrological data were used in the qualitative analysis of land use pattern on soil and water loss. The land use pattern change periods were identified by double mass curves of rainfall-runoff and rainfall erosivity-sediment. The characters of land use patterns were denoted by the spatial distribution of C value on slope grade and the distance to rivers, and the change of soil and water loss in different periods were analyzed by the increased ratio of rainfall runoff, rainfall erosivity sediment discharge. The results showed that: (1) During the periods of 1981-2000, there was a sharp change in 1990～1991, and the land use status in 1980s and 1990s could be reflected by the land use maps in 1985 and 1995 respectively. (2) From 1980s to 1990s, the C value in Xinghe watershed increased obviously, especially on steeper slope grades and at the close distances to the rivers. (3) The change of land use pattern altered the relationships of rainfall-runoff, rainfall erosivity-sediment discharge obviously; runoff and sediment discharge in flood season increased from 1980s to 1990s, though rainfall and rainfall erosivity decreased in the same periods. In order to reduce soil and water loss, not only land use types should be changed, but also more attentions should be paid to spatial distribution of land use types. It is necessary to increase the land use types with lower C value on steeper slope grades and at the close distances to the rivers. The results of denoting land use pattern and soil water loss were suited with each other, which means the methods could be used in the qualitative analysis of land use pattern and soil water loss. At the same time, the method of denoting soil and water loss omitted the spatial variation of rainfall, and may not be used in the large area with large variation of rainfall. Furthermore, more attentions should be paid to accuracy of C value of different land used types, interpretation of TM data and change of land use conditions in further study.