[Spatiotemporal variation of soil moisture in a small watershed of loess hilly region].

Based on field determinations, the spatiotemporal variation of soil moisture content in a small watershed of loess hilly region from 2002 to 2005 was studied, with the main affecting factors analyzed. The results showed that in the study area, the mean annual soil moisture profile was in an inverse L shape, with the lowest value at the depth of 1 m. The soil moisture contents between the layers of 0-0.2 m and below 2.4 m in different years, and those between the layers of 0-0.2 m and 1.0-2.4 m in different seasons were significantly different. In drought years, the lack of precipitation increased the spatial heterogeneity of soil moisture content in the layers of 1.0-2.4 m and below 2.4 m significantly; while in rainy years, the supplement of precipitation decreased the spatial heterogeneity of soil moisture content in 0-0.2 m layer, but had less effects on that in the layers of 1.0-2.4 m and below 2.4 m. Slope aspect and land use were the two main factors affecting the spatiotemporal variation of soil moisture content, while slope position had less effects. In drought years or by the end of drought season, the effects of slope aspect on soil moisture content decreased, while those of land use type increased with soil depth. In rainy years or by the end of rainy season, slope aspect became the most important affecting factor, while land use type only affected upper soil layer.